Measurement of transverse energy-energy correlations in multi-jet events in pp collisions at √s = 7 TeV using the ATLAS detector and determination of the strong coupling constant αs(mZ)

Wed 05 Dec 2018 11:04:17 KRAT

High transverse momentum jets produced in pp collisions at a centre of mass energy of 7 TeV are used to measure the transverse energy–energy correlation function and its associated azimuthal asymmetry. The data were recorded with the ATLAS detector at the LHC in the year 2011 and correspond to an integrated luminosity of 158 pb−1. The selection criteria demand the average transverse momentum of the two leading jets in an event to be larger than 250 GeV. The data at detector level are well described by Monte Carlo event generators. They are unfolded to the particle level and compared with theoretical calculations at next-to-leading-order accuracy. The agreement between data and theory is good and provides a precision test of perturbative Quantum Chromodynamics at large momentum transfers. From this comparison, the strong coupling constant given at the Z boson mass is determined to be View the MathML source.

Performance of the ATLAS muon trigger in pp collisions at √s=8 TeV

Wed 05 Dec 2018 11:04:06 KRAT

The performance of the ATLAS muon trigger system is evaluated with proton–proton collision data collectedin 2012 at the Large Hadron Collider at a centre-of-mass energy of 8 TeV. It is primarily evaluated using events containing a pair of muons from the decay of Z bosons. The efficiency of the single-muon trigger is measured for muons with transverse momentum 25 < pT < 100 GeV, with a statistical uncertainty of less than 0.01 % and a systematic uncertainty of 0.6 %. The pT range for efficiency determination is extended by using muons from decays of J/ψ mesons, W bosons, and top quarks. The muon trigger shows highly uniform and stable performance. The performance is compared to the prediction of a detailed simulation.

Observation and measurement of Higgs boson decays to WW* with the ATLAS detector

Wed 05 Dec 2018 10:57:06 KRAT

We report the observation of Higgs boson decays to WW based on an excess over background of 6.1 standard deviations in the dilepton final state, where the Standard Model expectation is 5.8 standard deviations. Evidence for the vector-boson fusion (VBF) production process is obtained with a significance of 3.2 standard deviations. The results are obtained from a data sample corresponding to an integrated luminosity of 25 fb−1 from pffisffiffi ¼ 7 and 8 TeV pp collisions recorded by the ATLAS detector at the LHC. For a Higgs boson mass of 125.36 GeV, the ratio of the measured value to the expected value of the total production cross section times branching fraction is 1.09þ0.16 −0.15 ðstatÞþ0.17 −0.14 ðsystÞ. The corresponding ratios for the gluon fusion and vector-boson fusion production mechanisms are 1.02 0.19ðstatÞþ0.22 −0.18 ðsystÞ and 1.27þ0.44 −0.40 ðstatÞþ0.30 −0.21 ðsystÞ, respectively. At ffiffiffips ¼ 8 TeV, the total production cross sections are measured to be σðgg→H→WWÞ¼4.60.9ðstatÞþ0.8 −0.7 ðsystÞ pb and σðVBF H → WWÞ ¼ 0.51þ0.17 −0.15 ðstatÞþ0.13 −0.08 ðsystÞ pb. The fiducial cross section is determined for the gluon-fusion process in exclusive final states with zero or one associated jet.

Measurement of three-jet production cross-sections in pp collisions at 7 TeV centre-of-mass energy using the ATLAS detector

Wed 05 Dec 2018 10:50:05 KRAT

Double-differential three-jet production cross-sections are measured in proton–proton collisions at a centre-of-mass energy of √s = 7 TeV using the ATLAS detector at the large hadron collider. The measurements are presented as a function of the three-jet mass (mjjj), in bins of the sum of the absolute rapidity separations between the three leading jets (Y ∗). Invariant masses extending up to 5 TeV are reached for 8 < Y ∗ < 10. These measurements use a sample of data recorded using the ATLAS detector in 2011, which corresponds to an integrated luminosity of 4.51 fb−1. Jets are identified using the anti-kt algorithm with two different jet radius parameters, R = 0.4 and R = 0.6. The dominant uncertainty in these measurements comes from the jet energy scale. Next-to-leading-order QCD calculations corrected to account for non-perturbative effects are compared to the measurements. Good agreement is found between the data and the theoretical predictions based on most of the available sets of parton distribution functions, over the full kinematic range, covering almost seven orders of magnitude in the measured cross-section values.

Measurement of the t¯t production cross-section as a function of jet multiplicity and jet transverse momentum in 7 TeV proton-proton collisions with the ATLAS detector

Wed 05 Dec 2018 10:15:26 KRAT

The t¯t production cross-section dependence on jet multiplicity and jet transverse momentum is reported for proton-proton collisions at a centre-of-mass energy of 7TeV in the single-lepton channel. The data were collected with the ATLAS detector at the CERN Large Hadron Collider and comprise the full 2011 data sample corresponding to an integrated luminosity of 4.6 fb−1. Differential cross-sections are presented as a function of the jet multiplicity for up to eight jets using jet transverse momentum thresholds of 25, 40, 60, and 80GeV, and as a function of jet transverse momentum up to the fifth jet. The results are shown after background subtraction and corrections for all known detector effects, within a kinematic range closely matched to the experimental acceptance. Several QCD-based Monte Carlo models are compared with the results. Sensitivity to the parton shower modelling is found at the higher jet multiplicities, at high transverse momentum of the leading jet and in the transverse momentum spectrum of the fifth leading jet. The MC@NLO+HERWIG MC is found to predict too few events at higher jet multiplicities.

Measurement of the branching ratio Γ(Λ0b → ψ(2S)Λ0)/Γ(Λ0b → J/ψΛ0) with the ATLAS detector

Wed 05 Dec 2018 10:15:10 KRAT

An observation of the View the MathML source decay and a comparison of its branching fraction with that of the View the MathML source decay has been made with the ATLAS detector in proton–proton collisions at View the MathML source at the LHC using an integrated luminosity of 20.6 fb−1. The J/ψ and ψ(2S) mesons are reconstructed in their decays to a muon pair, while the Λ0→pπ− decay is exploited for the Λ0 baryon reconstruction. The View the MathML source baryons are reconstructed with transverse momentum pT>10 GeV and pseudorapidity |η|<2.1. The measured branching ratio of the View the MathML source and View the MathML source decays is View the MathML source, lower than the expectation from the covariant quark model.

Measurement of charged-particle spectra in Pb+Pb collisions at √sNN = 2.76 TeV with the ATLAS detector at the LHC

Wed 05 Dec 2018 10:15:06 KRAT

Charged-particle spectra obtained in 0.15 nb−1 of Pb+Pb interactions at sNN−−−√=2.76TeV and 4.2 pb−1 of pp interactions at s√=2.76 TeV with the ATLAS detector at the LHC are presented in a wide transverse momentum (0.5

Jet energy measurement and its systematic uncertainty in proton-proton collisions at √s = 7 TeV with the ATLAS detector

Wed 05 Dec 2018 10:08:27 KRAT

The jet energy scale (JES) and its systematic uncertainty are determined for jets measured with the ATLAS detector using proton–proton collision data with a centre-ofmass energy of √s = 7 TeV corresponding to an integrated luminosity of 4.7 f −1. Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti-kt algorithm with distance parameters R = 0.4 or R = 0.6, and are calibrated using MC simulations. A residual JES correction is applied to account for differences between data and MC simulations. This correction and its systematic uncertainty are estimated using a combination of in situ techniques exploiting the transverse momentum balance between a jet and a reference object such as a photon or a Z boson, for 20 ≤ p jet T < 1000 GeV and pseudorapidities |η| < 4.5. The effect of multiple proton–proton interactions is corrected for, and an uncertainty is evaluated using in situ techniques. The smallest JES uncertainty of less than 1 % is found in the central calorimeter region (|η| < 1.2) for jets with 55 ≤ p jet T < 500 GeV. For central jets at lower pT, the uncertainty is about 3 %. A consistent JES estimate is found using measurements of the calorimeter response of single hadrons in proton–proton collisions and test-beam data, which also provide the estimate for p

Measurement of the production and lepton charge asymmetry of W bosons in Pb+Pb collisions at √ sNN = 2.76 TeV with the ATLAS detector

Wed 05 Dec 2018 10:08:15 KRAT

A measurement of W boson production in leadlead collisions at √sNN = 2.76 TeV is presented. It is based on the analysis of data collected with the ATLAS detector at the LHC in 2011 corresponding to an integrated luminosity of 0.14 nb−1 and 0.15 nb−1 in the muon and electron decay channels, respectively. The differential production yields and lepton charge asymmetry are each measured as a function of the average number of participating nucleons Npart and absolute pseudorapidity of the charged lepton. The results are compared to predictions based on next-to-leading-order QCD calculations. These measurements are, in principle, sensitive to possible nuclear modifications to the parton distribution functions and also provide information on scaling of W boson production in multi-nucleon systems.

Measurement of the transverse polarization of Λ and Λ¯ hyperons produced in proton-proton collisions at √s=7 TeV using the ATLAS detector

Wed 05 Dec 2018 10:01:14 KRAT

The transverse polarization of Λ and Λ¯ hyperons produced in proton-proton collisions at a center-ofmass energy of 7 TeV is measured. The analysis uses 760 μb−1 of minimum bias data collected by the ATLAS detector at the LHC in the year 2010. The measured transverse polarization averaged over Feynman xF from 5 × 10−5 to 0.01 and transverse momentum pT from 0.8 to 15 GeV is −0.010 0.005ðstatÞ 0.004ðsystÞ for Λ and 0.002 0.006ðstatÞ 0.004ðsystÞ for Λ¯ . It is also measured as a function of xF and pT, but no significant dependence on these variables is observed. Prior to this measurement, the polarization was measured at fixed-target experiments with center-of-mass energies up to about 40 GeV. The ATLAS results are compatible with the extrapolation of a fit from previous

Measurement of the top quark mass in the tt¯ → lepton+jets and tt¯ → dilepton channels using √s = 7 TeV ATLAS data

Wed 05 Dec 2018 10:01:08 KRAT

The top quark mass was measured in the channels t ¯t → lepton+jets and t ¯t → dilepton (lepton = e,μ)

Measurement of the production of neighbouring jets in lead-lead collisions at √sNN = 2.76 TeV with the ATLAS detector

Wed 05 Dec 2018 10:01:07 KRAT

This Letter presents measurements of correlated production of nearby jets in Pb+Pb collisions at View the MathML source using the ATLAS detector at the Large Hadron Collider. The measurement was performed using 0.14 nb−1 of data recorded in 2011. The production of correlated jet pairs was quantified using the rate, RΔR, of “neighbouring” jets that accompany “test” jets within a given range of angular distance, ΔR , in the pseudorapidity–azimuthal angle plane. The jets were measured in the ATLAS calorimeter and were reconstructed using the anti-kt algorithm with radius parameters d=0.2, 0.3, and 0.4. RΔR was measured in different Pb+Pb collision centrality bins, characterized by the total transverse energy measured in the forward calorimeters. A centrality dependence of RΔR is observed for all three jet radii with RΔR found to be lower in central collisions than in peripheral collisions. The ratios formed by the RΔR values in different centrality bins and the values in the 40–80% centrality bin are presented.

Measurement of exclusive γγ→ℓ+ℓ- production in proton-proton collisions at √s = 7 TeV with the ATLAS detector

Wed 05 Dec 2018 09:47:08 KRAT

This Letter reports a measurement of the exclusive γγ→ℓ+ℓ− (ℓ=e, μ) cross-section in proton–proton collisions at a centre-of-mass energy of 7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of 4.6 fb−1. For the electron or muon pairs satisfying exclusive selection criteria, a fit to the dilepton acoplanarity distribution is used to extract the fiducial cross-sections. The cross-section in the electron channel is determined to be View the MathML source for a phase–space region with invariant mass of the electron pairs greater than 24 GeV, in which both electrons have transverse momentum pT>12 GeV and pseudorapidity |η|<2.4. For muon pairs with invariant mass greater than 20 GeV, muon transverse momentum pT>10 GeV and pseudorapidity |η|<2.4, the cross-section is determined to be View the MathML source. When proton absorptive effects due to the finite size of the proton are taken into account in the theory calculation, the measured cross-sections are found to be consistent with the theory prediction.

Measurement of the inclusive jet cross-section in proton-proton collisions at √s=7 TeV using 4.5 fb-1 of data with the ATLAS detector

Wed 05 Dec 2018 09:40:37 KRAT

The inclusive jet cross-section is measured in proton-proton collisions at acentre-of-mass energy of 7TeV using a data set corresponding to an integrated luminosity of 4.5 fb−1 collected with the ATLAS detector at the Large Hadron Collider in 2011. Jets are identified using the anti-kt algorithm with radius parameter values of 0.4 and 0.6. The double-differential cross-sections are presented as a function of the jet transverse momentum and the jet rapidity, covering jet transverse momenta from 100 GeV to 2TeV. Next-to-leading-order QCD calculations corrected for non-perturbative effects and electroweak effects, as well as Monte Carlo simulations with next-to-leading-order matrix elements interfaced to parton showering, are compared to the measured cross-sections. A quantitative comparison of the measured cross-sections to the QCD calculations using several sets of parton distribution functions is performed.

Measurement of the forward-backward asymmetry of electron and muon pair-production in pp collisions at √s = 7 TeV with the ATLAS detector

Wed 05 Dec 2018 09:40:30 KRAT

This paper presents measurements from the ATLAS experiment of the forward-backward asymmetry in the reaction pp→Z/γ∗→l+l−, with l being electrons or muons, and the extraction of the effective weak mixing angle. The results are based on the full set of data collected in 2011 in pp collisions at the LHC at s√ = 7 TeV, corresponding to an integrated luminosity of 4.8 fb−1. The measured asymmetry values are found to be in agreement with the corresponding Standard Model predictions. The combination of the muon and electron channels yields a value of the effective weak mixing angle of 0.2308±0.0005(stat.)±0.0006(syst.)±0.0009(PDF), where the first uncertainty corresponds to data statistics,the second to systematic effects and the third to knowledge of the parton density functions. This result agrees with the current world average from the Particle Data Group fit.

Measurement of the charge asymmetry in dileptonic decays of top quark pairs in pp collisions √s = 7 TeV using the ATLAS detector

Wed 05 Dec 2018 09:40:17 KRAT

A measurement of the top–antitop (tt¯) charge asymmetry is presented using data corresponding to an integrated luminosity of 4.6 fb−1 of LHC pp collisions at a centre of mass energy of 7 TeV collected by the ATLAS detector. Events with two charged leptons, at least two jets and large missing transverse momentum are selected. Two observables are studied: A``C based on the identified charged leptons, and Att¯C , based on the reconstructed tt¯ final state. The asymmetries are measured to be A``C = 0.024 ± 0.015 (stat.) ± 0.009 (syst.), A tt¯ C = 0.021 ± 0.025 (stat.) ± 0.017 (syst.).The measured values are in agreement with the Standard Model predictions.

Measurement of the top pair production cross section in 8 TeV proton-proton collisions using kinematic information in the lepton+jets final state with ATLAS

Wed 05 Dec 2018 09:33:15 KRAT

A measurement is presented of the t¯t inclusive production cross section in pp collisions at a center-ofmass energy of √s=8 TeV using data collected by the ATLAS detector at the CERN Large Hadron Collider. The measurement was performed in the lepton þ jets final state using a data set corresponding to an integrated luminosity of 20.3 fb−1. The cross section was obtained using a likelihood discriminant fit and b-jet identification was used to improve the signal-to-background ratio. The inclusive t¯t production cross section was measured to be 260 1ðstatÞþ22−23 ðstatÞ 8ðlumiÞ 4ðbeamÞ pb assuming a top-quark mass of 172.5 GeV, in good agreement with the theoretical prediction of 253þ13−15 pb. The t¯t → ðe; μÞ þ jets production cross section in the fiducial region determined by the detector acceptance is also reported.

Identification and energy calibration of hadronically decaying tau leptons with the ATLAS experiment in pp collisions at √s=8 TeV

Wed 05 Dec 2018 09:33:11 KRAT

This paper describes the trigger and offline reconstruction, identification and energy calibration algorithms for hadronic decays of tau leptons employed for the data collected from pp collisions in 2012 with the ATLAS detector at the LHC center-of-mass energy√s = 8 TeV. The performance of these algorithms is measured in most cases with Z decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fb−1. An uncertainty on the offline reconstructed tau energy scale of 2–4%, depending on transverse energy and pseudorapidity, is achieved using two independent methods. The offline tau identification efficiency is measured with a precision of 2.5% for hadronically decaying tau leptons with one associated track, and of 4% for the case of three associated tracks, inclusive in pseudorapidity and for a visible transverse energy greater than 20 GeV. For hadronic tau lepton decays selected by offline algorithms, the tau trigger identification efficiency is measured with a precision of 2–8%, depending on the transverse energy. The performance of the tau algorithms, both offline and at the trigger level, is found to be stable with respect to the number of concurrent proton–proton interactions and has supported a variety of physics results using hadronically decaying tau leptons at ATLAS.

Measurement of spin correlation in top-antitop quark events and search for top squark pair production in pp collisions at √s =8 TeV using the ATLAS detector

Wed 05 Dec 2018 09:33:05 KRAT

A measurement of spin correlation in t¯t production is presented using data collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb−1. The correlation between the top and antitop quark spins is extracted from dilepton t¯t events by using the difference in the azimuthal angle between the two charged leptons in the laboratory frame. In the helicity basis the measured degree of correlation

Measurement of the correlation between flow harmonics of different order in lead-lead collisions at √sNN = 2.76 TeV with the ATLAS detector

Tue 04 Dec 2018 10:33:39 KRAT

Correlations between the elliptic or triangular flow coefficients vm (m=2 or 3) and other flow harmonics vn (n=2 to 5) are measured using sNN−−−√=2.76 TeV Pb+Pb collision data collected in 2010 by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 7 μb−1. The vm−vn correlations are measured in midrapidity as a function of centrality, and, for events within the same centrality interval, as a function of event ellipticity or triangularity defined in a forward rapidity region. For events within the same centrality interval, v3 is found to be anticorrelated with v2 and this anticorrelation is consistent with similar anticorrelations between the corresponding eccentricities, ε2 and ε3. However, it is observed that v4 increases strongly with v2, and v5 increases strongly with both v2 and v3. The trend and strength of the vm−vn correlations for n=4 and 5 are found to disagree with εm−εn correlations predicted by initial-geometry models. Instead, these correlations are found to be consistent with the combined effects of a linear contribution to vn and a nonlinear term that is a function of v22 or of v2v3, as predicted by hydrodynamic models. A simple two-component fit is used to separate these two contributions. The extracted linear and nonlinear contributions to v4 and v5 are found to be consistent with previously measured event-plane correlations.

Measurement of the tt¯W and tt¯Z production cross sections in pp collisions at √s = 8 TeV with the ATLAS detector

Tue 04 Dec 2018 10:20:08 KRAT

The production cross sections of top-quark pairs in association with massive vector bosons have been measured using data from pp collisions at s√=8s=8 TeV. The dataset corresponds to an integrated luminosity of 20.3 fb−1 collected by the ATLAS detector in 2012 at the LHC. Final states with two, three or four leptons are considered. A fit to the data considering the tt¯Wtt¯W and tt¯Ztt¯Z processes simultaneously yields a significance of 5.0σ (4.2σ) over the background-only hypothesis for tt¯Wtt¯W ( tt¯Ztt¯Z ) production. The measured cross sections are σtt¯W=369+100−91σtt¯W=369−91+100 fb and σtt¯Z=176+58−52σtt¯Z=176−52+58 fb. The background-only hypothesis with neither tt¯Wtt¯W nor tt¯Ztt¯Z production is excluded at 7.1σ. All measurements are consistent with next-to-leading-order calculations for the tt¯Wtt¯W and tt¯Ztt¯Z processes.

Measurement of the top-quark mass in the fully hadronic decay channel from ATLAS data at √ s = 7 TeV

Tue 04 Dec 2018 10:19:40 KRAT

The mass of the top quark is measured in a data set corresponding to 4.6 fb−1 of proton–proton collisionswith centre-of-mass energy √s = 7 TeV collected by the ATLAS detector at the LHC. Events consistent with hadronic decays of top–antitop quark pairs with at least six jets in the final state are selected. The substantial background from multijet production is modelled with data-driven methods that utilise the number of identified b-quark jets and the transverse momentum of the sixth leading jet, which have minimal correlation. The top-quark mass is obtained from template fits to the ratio of three-jet to dijet mass. The three-jet mass is calculated from the three jets produced in a top-quark decay.Using these three jets the dijet mass is obtained from the

Measurement of colour flow with the jet pull angle in t t¯ events using the ATLAS detector at √s = 8 TeV

Tue 04 Dec 2018 10:12:45 KRAT

The distribution and orientation of energy inside jets is predicted to be an experimental handle on colour connections between the hard--scatter quarks and gluons initiating the jets. This Letter presents a measurement of the distribution of one such variable, the jet pull angle. The pull angle is measured for jets produced in tt¯ events with one W boson decaying leptonically and the other decaying to jets using 20.3 fb−1 of data recorded with the ATLAS detector at a centre-of-mass energy of s√=8 TeV at the LHC. The jet pull angle distribution is corrected for detector resolution and acceptance effects and is compared to various models.

Evidence of Wγγ production in pp collisions at √s = 8 TeV and limits on anomalous quartic Gauge couplings with the ATLAS detector

Tue 04 Dec 2018 09:51:49 KRAT

This Letter reports evidence of triple gauge boson production pp ^ W(fv)yy + X, which is accessible for the first time with the 8 TeV LHC data set. The fiducial cross section for this process is measured in a data sample corresponding to an integrated luminosity of 20.3 fb-1, collected by the ATLAS detector in 2012. Events are selected using the W boson decay to ev or ^v as well as requiring two isolated photons. The measured cross section is used to set limits on anomalous quartic gauge couplings in the high diphoton mass region.

Measurement of differential J/ψ production cross sections and forward-backward ratios in p + Pb collisions with the ATLAS detector

Thu 06 Dec 2018 16:00:07 KRAT

Measurements of differential cross sections for J/ψ production in p + Pb collisions at √SNN = 5.02 TeV at the CERN Large Hadron Collider with the ATLAS detector are presented. The data set used corresponds to an integrated luminosity of 28.1 nb-1. The J/ψ mesons are reconstructed in the dimuon decay channel over the transverse momentum range 8 < pT < 30 GeV and over the center-of-mass rapidity range -2.87 < y* < 1.94. Prompt J/ψ are separated from J/ψ resulting from b-hadron decays through an analysis of the distance between the J/ψ decay vertex and the event primary vertex. The differential cross section for production of nonprompt J/ψ is compared to a FONLL calculation that does not include nuclear effects. Forward-backward production ratios are presented and compared to theoretical predictions. These results complement previously published results by covering a region of higher transverse momentum and more central rapidity. They thus constrain the kinematic dependence of nuclear modifications of charmonium and b-quark production in p + Pb collisions.

Observation of top-quark pair production in association with a photon and measurement of the tt¯γ production cross section in pp collisions at √s =7 TeV using the ATLAS detector

Thu 06 Dec 2018 11:34:31 KRAT

A search is performed for top-quark pairs (t¯t) produced together with a photon (γ) with transverse energy greater than 20 GeV using a sample of t¯t candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of 4.59 fb−1 of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total, 140 and 222 t¯tγ candidate events are observed in the electron and muon channels, to be compared to the expectation of 79 26 and 120 39 non-t¯tγ background events, respectively. The production of t¯tγ events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The t¯tγ production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is σfid t¯tγ × BR ¼ 63 8ðstatÞþ17 −13 ðsystÞ 1ðlumiÞ fb per lepton flavor, in good agreement with the leadingorder theoretical calculation normalized to the next-to-leading-order theoretical prediction of 48 10 fb.

Measurements of the nuclear modification factor for jets in Pb+Pb collisions at √sNN = 2.76 TeV with the ATLAS detector

Thu 06 Dec 2018 11:34:23 KRAT

Measurements of inclusive jet production are performed in pp and Pb+Pb collisions at sNN−−−√=2.76 TeV with the ATLAS detector at the LHC, corresponding to integrated luminosities of 4.0 and 0.14 nb−1, respectively. The jets are identified with the anti-kt algorithm with R=0.4, and the spectra are measured over the kinematic range of jet transverse momentum 32

Observation and measurements of the production of prompt and non-prompt J/ψ mesons in association with a Z boson in pp collisions at √s = 8 TeV with the ATLAS detector

Thu 06 Dec 2018 11:27:09 KRAT

The production of a Z boson in association with a J/ψ meson in proton–proton collisions probes the productionmechanisms of quarkonium and heavy flavour in association with vector bosons, and allows studies of multiple parton scattering. Using 20.3 fb−1 of data collected with the ATLAS experiment at the LHC in pp collisions at √s = 8 TeV, the first measurement of associated Z + J/ψ production is presented for both prompt and non-prompt J/ψ production, with both signatures having a significance in excess of 5σ. The inclusive production cross-sections for Z boson production (analysed inμ+μ− or e+e− decay modes) in association with prompt and non-prompt J/ψ(→ μ+μ−) are measured relative to the inclusive production rate of Z bosons in the same fiducial volume to be (36.8 ± 6.7 ± 2.5) × 10−7 and (65.8 ± 9.2 ± 4.2) × 10−7 respectively. Normalised differential production cross-section ratios are also determined as a function of the J/ψ transverse momentum. The fraction of signal events arising from single and double parton scattering is estimated, and a lower limit of 5.3 (3.7) mb at 68 (95)% confidence level is placed on the effective cross-section regulating double parton interactions.

Measurement of the WW + W Z cross section and limits on anomalous triple gauge couplings using final states with one lepton, missing transverse momentum, and two jets with the ATLAS detector at √s=7 TeV

Thu 06 Dec 2018 10:59:06 KRAT

The production of a W boson decaying to e or μ in association with a W or Z boson decaying to two jets is studied using 4.6 fb−1 of proton-proton collision data at √s=7 TeV recorded with the ATLAS detector at the LHC. The combined WW+WZ cross section is measured with a significance of 3.4 and is found to be 68±7 (stat.)±19 (syst.) pb, in agreement with the Standard Model expectation of 61.1±2.2 pb. The distribution of the transverse momentum of the dijet system is used to set limits on anomalous contributions to the triple gauge coupling vertices and on parameters of an effective-field-theory model.

Search for new phenomena in events with three or more charged leptons in pp collisions at √s = 8 TeV with the ATLAS detector

Sat 12 May 2018 11:45:34 KRAT

A generic search for anomalous production of events with at least three charged leptons is presented. The data sample consists of pp collisions at s√=8 TeV collected in 2012 by the ATLAS experiment at the CERN Large Hadron Collider, and corresponds to an integrated luminosity of 20.3 fb−1. Events are required to have at least three selected lepton candidates, at least two of which must be electrons or muons, while the third may be a hadronically decaying tau. Selected events are categorized based on their lepton flavour content and signal regions are constructed using several kinematic variables of interest. No significant deviations from Standard Model predictions are observed. Model-independent upper limits on contributions from beyond the Standard Model phenomena are provided for each signal region, along with prescription to re-interpret the limits for any model. Constraints are also placed on models predicting doubly charged Higgs bosons and excited leptons. For doubly charged Higgs bosons decaying to eτ or μτ, lower limits on the mass are set at 400 GeV at 95% confidence level. For excited leptons, constraints are provided as functions of both the mass of the excited state and the compositeness scale Λ, with the strongest mass constraints arising in regions where the mass equals Λ. In such scenarios, lower mass limits are set at 3.0 TeV for excited electrons and muons, 2.5 TeV for excited taus, and 1.6 TeV for every excited-neutrino flavour.

Search for a new resonance decaying to a W or Z boson and a Higgs boson in the : ar{b}. u / u u + b

Sat 12 May 2018 11:45:33 KRAT

A search for a new resonance decaying to a W or Z boson and a Higgs boson in the ℓℓ/ℓν/νν+bb¯ final states is performed using 20.3 fb −1 of pp collision data recorded at s√= 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the WH / ZH invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets.

Search for high-mass diboson resonances with boson-tagged jets in proton-proton collisions at √s = 8 TeV with the ATLAS detector

Mon 23 Apr 2018 15:54:54 KRAT

A search is performed for narrow resonances decaying into WW, WZ, or ZZ boson pairs using 20.3 fb−1 of proton-proton collision data at a centre-of-mass energy of s√=8 TeV recorded with the ATLAS detector at the Large Hadron Collider. Diboson resonances with masses in the range from 1.3 to 3.0 TeV are sought after using the invariant mass distribution of dijets where both jets are tagged as a boson jet, compatible with a highly boosted W or Z boson decaying to quarks, using jet mass and substructure properties. The largest deviation from a smoothly falling background in the observed dijet invariant mass distribution occurs around 2 TeV in the WZ channel, with a global significance of 2.5 standard deviations. Exclusion limits at the 95% confidence level are set on the production cross section times branching ratio for the WZ final state of a new heavy gauge boson, W′, and for the WW and ZZ final states of Kaluza-Klein excitations of the graviton in a bulk Randall-Sundrum model, as a function of the resonance mass. W′ bosons with couplings predicted by the extended gauge model in the mass range from 1.3 to 1.5 TeV are excluded at 95% confidence level.

ATLAS Run 1 searches for direct pair production of third-generation squarks at the Large Hadron Collider

Mon 21 Aug 2017 16:00:14 KRAT

This paper reviews and extends searches for the direct pair production of the scalar supersymmetric partners of the top and bottom quarks in proton–proton collisions collected by the ATLAS collaboration during the LHC Run 1. Most of the analyses use 20 fb−1 of collisions at a centre-of-mass energy of √s=8 TeV, although in some case an additional 4.7 fb−1 of collision data at √s=7 TeV are used. New analyses are introduced to improve the sensitivity to specific regions of the model parameter space. Since no evidence of third-generation squarks is found, exclusion limits are derived by combining several analyses and are presented in both a simplified model framework, assuming simple decay chains, as well as within the context of more elaborate phenomenological supersymmetric models.

Study of (W/Z)H production and Higgs boson couplings using H→WW* decays with the ATLAS detector

Mon 19 Nov 2018 12:50:29 KRAT

A search for Higgs boson production in association with a W or Z boson, in the H→ W W ∗ decay channel, is performed with a data sample collected with the ATLAS detector at the LHC in proton-proton collisions at centre-of-mass energies s√=7 TeV and 8 TeV, corresponding to integrated luminosities of 4.5 fb−1 and 20.3 fb−1, respectively. The WH production mode is studied in two-lepton and three-lepton final states, while two- lepton and four-lepton final states are used to search for the ZH production mode. The observed significance, for the combined W H and ZH production, is 2.5 standard deviations while a significance of 0.9 standard deviations is expected in the Standard Model Higgs boson hypothesis. The ratio of the combined W H and ZH signal yield to the Standard Model expectation, μ V H , is found to be μ V H = 3.0 − 1.1 + 1.3 (stat.) − 0.7 + 1.0 (sys.) for the Higgs boson mass of 125.36 GeV. The W H and ZH production modes are also combined with the gluon fusion and vector boson fusion production modes studied in the H → W W ∗ → ℓνℓν decay channel, resulting in an overall observed significance of 6.5 standard deviations and μ ggF + VBF + VH = 1. 16 − 0.15 + 0.16 (stat.) − 0.15 + 0.18 (sys.). The results are interpreted in terms of scaling factors of the Higgs boson couplings to vector bosons (κ V ) and fermions (κ F ); the combined results are: |κ V | = 1.06 − 0.10 + 0.10 , |κ F | = 0. 85 − 0.20 + 0.26 .

Erratum: Measurement of the inclusive jet cross-section in proton-proton collisions at √s = 7 TeV using 4.5 fb-1 of data with the ATLAS detector

Mon 16 Dec 2019 15:01:26 KRAT

Erratum to: JHEP02(2015)153. It was found that the non-perturbative corrections calculated using Pythia with the Perugia 2011 tune did not include the effect of the underlying event. The affected correction factors were recomputed using the Pythia 6.427 generator. These corrections are applied as baseline to the NLO pQCD calculations and thus the central values of the theoretical predictions have changed by a few percent with the new corrections. This has a minor impact on the agreement between the data and the theoretical predictions. Figures 2 and 6 to 13, and all the tables have been updated with the new values. A few sentences in the discussion in sections 5.2 and 9 were altered or removed.

Searches for heavy long-lived charged particles with the ATLAS detector in proton-proton collisions at √s=8 TeV

Mon 10 Dec 2018 13:06:36 KRAT

Searches for heavy long-lived charged particles are performed using a data sample of 19.1 fb−1 from proton-proton collisions at a centre-of-mass energy of ps = 8TeV collected by the ATLAS detector at the Large Hadron Collider. No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for tan between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered.

Search for new phenomena in the dijet mass distribution using pp collision data at √s=8 TeV with the ATLAS detector

Mon 10 Dec 2018 13:06:14 KRAT

Dijet events produced in LHC proton-proton collisions at a center-of-mass energy √s=8 TeV are studied with the ATLAS detector using the full 2012 data set, with an integrated luminosity of 20.3 fb−1. Dijet masses up to about 4.5 TeV are probed. No resonancelike features are observed in the dijet mass spectrum. Limits on the cross section times acceptance are set at the 95% credibility level for various hypotheses of new phenomena in terms of mass or energy scale, as appropriate. This analysis excludes excited quarks with a mass below 4.06 TeV, color-octet scalars with a mass below 2.70 TeV, heavy W0 bosons with a mass below 2.45 TeV, chiral w bosons with a mass below 1.75 TeV, and quantum black holes with six extra space-time dimensions with threshold mass below 5.66 TeV.

Search for production of WW/WZ resonances decaying to a lepton, neutrino and jets in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 13:06:12 KRAT

A search is presented for narrow diboson resonances decaying to W W or W Z in the final state where one W boson decays leptonically (to an electron or a muon plus a neutrino) and the other W/Z boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb−1 of pp collisions at √s = 8 TeV collected by the

Search for type-III seesaw heavy leptons in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:59:54 KRAT

A search for the pair production of heavy leptons (N0; L) predicted by the type-III seesaw theory formulated to explain the origin of small neutrino masses is presented. The decay channels N0 → Wl∓ (l ¼ e; μ; τ) and L → Wν (ν ¼ νe; νμ; ντ) are considered. The analysis is performed using the final state that contains two leptons (electrons or muons), two jets from a hadronically decaying W boson and large missing transverse momentum. The data used in the measurement correspond to an integrated luminosity of 20.3 fb−1 of pp collisions at pffisffiffi ¼ 8 TeV collected by the ATLAS detector at the LHC. No evidence of heavy lepton pair production is observed. Heavy leptons with masses below 325–540 GeVare excluded at the 95% confidence level, depending on the theoretical scenario considered.

Search for s-channel single top-quark production in proton-proton collisions at √s=8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:59:21 KRAT

This Letter presents a search at the LHC for s-channel single top-quark production in proton–proton collisions at a centre-of-mass energy of 8TeV. The analyzeddata set was recorded by the ATLAS detector and corresponds to an integrated luminosity of 20.3fb−1. Selected events contain one charged lepton, large missing transverse momentum and exactly two b-tagged jets. A multivariate event classifier based on boosted decision trees is developed to discriminate s-channel single top-quark events from the main background contributions. The signal extraction is based on a binned maximum-likelihood fit of the output classifier distribution. The analysis leads to an upper limit on the s-channel single top-quark production cross-section of 14.6pb at the 95% confidence level. The fit gives a cross-section of σs=5.0 ±4.3pb, consistent with the Standard Model expectation.

Simultaneous measurements of the tt¯, W+W-, and Z/γ∗→ττ production cross-sections in pp collisions at √s=7 TeV with the ATLAS detector

Mon 10 Dec 2018 12:59:06 KRAT

Simultaneous measurements of the t¯t, WþW−, and Z=γ → ττ production cross-sections using an integrated luminosity of 4.6 fb−1 of pp collisions at √s=7 TeV collected by the ATLAS detector at the

Study of the spin and parity of the Higgs boson in diboson decays with the ATLAS detector

Mon 10 Dec 2018 12:53:06 KRAT

Studies of the spin, parity and tensor couplingsof the Higgs boson in the H → ZZ∗ → 4, H → WW∗ → eνμν and H → γγ decay processes at the LHC are presented. The investigations are based on 25 fb−1 of pp collision data collected by the ATLAS experiment at √s = 7 TeV and √s = 8 TeV. The Standard Model (SM) Higgs boson hypothesis, сorresponding to the quantum numbers J P = 0+, is tested against several alternative spin scenarios, including non-SM spin-0 and spin-2 models with universal and non-universal couplings to fermions and vector bosons. All tested alternative models are excluded in favour of the SM Higgs boson hypothesis at more than 99.9% confidence level. Using the H → ZZ∗ → 4 and H → WW∗ → eνμν decays, the tensor structure of the interaction between the spin-0 boson and the SM vector bosons is also investigated. The observed distributions of variables sensitive to the non-SM tensor couplings are compatible with the SM predictions and constraints on the non-SM couplings are derived.

Search for photonic signatures of gauge-mediated supersymmetry in 8 TeV pp collisions with the ATLAS detector

Mon 10 Dec 2018 12:52:58 KRAT

A search is presented for photonic signatures motivated by generalised models of gauge-mediated supersymmetry breaking. This search makes use of 20.3fb−1 of proton-proton collision data at s√=8 TeV recorded by the ATLAS detector at the LHC, and explores models dominated by both strong and electroweak production of supersymmetric partner states. Four experimental signatures incorporating an isolated photon and significant missing transverse momentum are explored. These signatures include events with an additional photon, lepton, b-quark jet, or jet activity not associated with any specific underlying quark flavor. No significant excess of events is observed above the Standard Model prediction and model-dependent 95% confidence-level exclusion limits are set.

Search for pair-produced long-lived neutral particles decaying to jets in the ATLAS hadronic calorimeter in pp collisions at √s = 8 TeV

Mon 10 Dec 2018 12:52:56 KRAT

The ATLAS detector at the Large Hadron Collider at CERN is used to search for the decay of a scalar boson to a pair of long-lived particles, neutral under the Standard Model gauge group, in 20.3fb−1of data collected in proton–proton collisions at √s=8 TeV. This search is sensitive to long-lived particles that decay to Standard Model particles producing jets at the outer edge of the ATLAS electromagnetic calorimeter or inside the hadronic calorimeter. No significant excess of events is observed. Limits are reported on the product of the scalar boson production cross section times branching ratio into long-lived neutral particles as a function of the proper lifetime of the particles. Limits are reported for boson masses from 100 GeV to 900 GeV, and a long-lived neutral particle mass from 10 GeV to 150 GeV.

Search for the Standard Model Higgs boson produced in association with top quarks and decaying into bb in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:44:01 KRAT

A search for the Standard Model Higgs boson produced in association with a top-quark pair, t ¯tH, is presented. The analysis uses 20.3 fb−1 of pp collision data at √s = 8 TeV, collected with the ATLAS detector at the Large Hadron Collider during 2012. The search is designed for the H b ¯b decay mode and uses events containing one or two electrons or muons. In order to improve the sensitivity of the search, events are categorised according to their jet and b-tagged jet multiplicities. A neural network is used to discriminate between signal and background events, the latter being dominated by t ¯t+jets production. In the single-lepton channel, variables calculated using a matrix element method are included as inputs to the neural network to improve discrimination of the irreducible t ¯t+b ¯b background. No significant excess of events above the background expectation is found and an observed (expected) limit of 3.4 (2.2) times the Standard Model cross section is obtained at 95% confidence level. The ratio of the measured t ¯tH signal cross section to the Standard Model expectation is found to be μ = 1.5±1.1 assuming a Higgs boson mass of 125 GeV .

Search for scalar charm quark pair production in pp collisions at √s =8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:31:28 KRAT

The results of a dedicated search for pair production of scalar partners of charm quarks are reported. The search is based on an integrated luminosity of 20.3 fb−1 of pp collisions at √s =8 TeV recorded with the ATLAS detector at the LHC. The search is performed using events with large missing transverse momentum and at least two jets, where the two leading jets are each tagged as originating from c quarks. Events containing isolated electrons or muons are vetoed. In an R-parity-conserving minimal supersymmetric scenario in which a single scalar-charm state is kinematically accessible, and where it decays exclusively into a charm quark and a neutralino, 95% confidence-level upper limits are obtained in the scalar-charm–neutralino mass plane such that, for neutralino masses below 200 GeV, scalar-charm masses

Search for supersymmetry in events containing a same-flavour opposite-sign dilepton pair, jets, and large missing transverse momentum in √s = 8TeV pp collisions with the ATLAS detector

Mon 10 Dec 2018 12:31:06 KRAT

Two searches for supersymmetric particles in final states containing a same-flavour opposite-sign lepton pair, jets and large missing transverse momentum are presented. The proton–proton collision data used in these searches were collected at a centre-of-mass energy √s = 8TeV by the ATLAS detector at the Large Hadron Collider and corresponds to an integrated luminosity of 20.3 fb−1. Two leptonic production mechanisms are considered: decays of squarks and gluinos with Z bosons in the final state, resulting in a peak in the dilepton invariant mass distribution around the Z-boson mass; and decays of neutralinos (e.g. χ˜02 → +−χ˜0 1 ), resulting in a kinematic endpoint in the dilepton invariant mass distribution. For the former, an excess of events above the expected Standard Model background is observed, with a significance of three standard deviations. In the latter case, the data are well-described by the expected Standard Model background. The results from each channel are interpreted in the context of several supersymmetric models involving the production of squarks and gluinos.

Search for the Xb and other hidden-beauty states in the π+π−Υ(1S) channel at ATLAS

Mon 10 Dec 2018 12:24:15 KRAT

This Letter presents a search for a hidden-beauty counterpart of the X(3872)in the mass ranges of 10.05–10.31 GeV and 10.40–11.00 GeV, in the channel Xb→π+π−Υ(1S)(→μ+μ−), using 16.2fb−1of √s=8TeVppcollision data collected by the ATLAS detector at the LHC. No evidence for new narrow states is found, and upper limits are set on the product of the Xb cross section and branching fraction, relative to those of the Υ(2S), at the 95% confidence level using the CLS approach. These limits range from 0.8% to 4.0%, depending on mass. For masses above 10.1 GeV, the expected upper limits from this analysis are the most restrictive to date. Searches for production of the Υ(13DJ), Υ(10 860), and Υ(11 020)states also reveal no significant signals.

Search for the b¯b decay of the Standard Model Higgs boson in associated (W/Z)H production with the ATLAS detector

Mon 10 Dec 2018 12:17:42 KRAT

A search for the b¯b decay of the Standard Model Higgs boson is performed with the ATLAS experiment using the full dataset recorded at the LHC in Run 1. The integrated luminosities used are 4.7 and 20.3 fb−1 from pp collisions at ps = 7 and 8TeV, respectively. The processes considered are associated (W/Z)H production, where W ! e/μ, Z ! ee/μμ and Z!. The observed (expected) deviation from the backgroundonly hypothesis corresponds to a significance of 1.4 (2.6) standard deviations and the ratio of the measured signal yield to the Standard Model expectation is found to be μ = 0.52 ± 0.32 (stat.) ± 0.24 (syst.) for a Higgs boson mass of 125.36 GeV. The analysis procedure is validated by a measurement of the yield of (W/Z)Z production with Z ! b¯b in the same final states as for the Higgs boson search, from which the ratio of the observed signal yield to the Standard Model expectation is found to be 0.74 ± 0.09 (stat.) ± 0.14 (syst.).

Search for W' → tb → qqbb decays in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:17:39 KRAT

A search for a massive W gauge boson decaying to a top quark and a bottom quark is performed with theATLAS detector in pp collisions at the LHC. The dataset was taken at a centre-of-mass energy of √s = 8 TeV and corresponds to 20.3 fb−1 of integrated luminosity. This analysis is done in the hadronic decay mode of the top quark, where novel jet substructure techniques are used to identify jets from high-momentum top quarks. This allows for a search for high-mass W bosons in the range 1.5–3.0 TeV. b-tagging is used to identify jets originating from b-quarks. The data are consistent with Standard Model background-only expectations,

Search for the associated production of the Higgs boson with a top quark pair in multilepton final states with the ATLAS detector

Mon 10 Dec 2018 12:17:10 KRAT

A search for the associated production of the Higgs boson with a top quark pair is performed in multilepton final states using 20.3 fb−1 of proton-proton collision data recorded by the ATLAS experiment at s√=8 TeV at the Large Hadron Collider. Five final states, targeting the decays H→WW∗, ττ, and ZZ∗, are examined for the presence of the Standard Model (SM) Higgs boson: two same-charge light leptons (e or μ) without a hadronically decaying τ lepton; three light leptons; two same-charge light leptons with a hadronically decaying τ lepton; four light leptons; and one light lepton and two hadronically decaying τ leptons. No significant excess of events is observed above the background expectation. The best fit for the tt¯H production cross section, assuming a Higgs boson mass of 125 GeV, is 2.1+1.4−1.2 times the SM expectation, and the observed (expected) upper limit at the 95% confidence level is 4.7 (2.4) times the SM rate. The p-value for compatibility with the background-only hypothesis is 1.8σ; the expectation in the presence of a Standard Model signal is 0.9σ.

Search for production of vector-like quark pairs and of four top quarks in the lepton-plus-jets final state in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:17:07 KRAT

A search for pair production of vector-like quarks, both up-type (T) and downtype (B), as well as for four-top-quark production, is presented. The search is based on pp collisions at √s=8 TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 20.3 fb−1. Data are analysed in the lepton-plus-jets final state, characterised by an isolated electron or muon with high transverse momentum, large missing transverse momentum and multiple jets. Dedicated analyses are performed targeting three cases: a T quark with significant branching ratio to a W boson and a b-quark (T ¯ T ! Wb+X), and both a T quark and a B quark with significant branching ratio to a Higgs boson and a third-generation quark

Search for W'->t¯b in the lepton plus jets final state in proton-proton collisions at a centre-of-mass energy of √s=8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:10:23 KRAT

A search for new charged massive gauge bosons, called W, is performed with the ATLAS detector at the LHC, in proton–proton collisions at a centre-of-mass energy of √s=8TeV, using a dataset corresponding to an integrated luminosity of 20.3fb−1. This analysis searches for Wbosons in the W→t¯bdecay channel in final states with electrons or muons, using a multivariate method based on boosted decision trees. The search covers masses between 0.5 and 3.0TeV, for right-handed or left-handed Wbosons. No significant deviation from the Standard Model expectation is observed and limits are set on the W→t¯bcross-section times branching ratio and on the W-boson effective couplings as a function of the W-boson mass using the CLsprocedure. For a left-handed (right-handed) Wboson, masses below 1.70 (1.92)TeVare excluded at 95% confidence level.

Search for massive, long-lived particles using multitrack displaced vertices or displaced lepton pairs in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:03:27 KRAT

Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. This article presents the results of a search for events containing at least one long-lived particle that decays at a significant distance from its production point into two leptons or into five or more charged particles. This analysis uses a data sample of proton-proton collisions at s√ = 8 TeV corresponding to an integrated luminosity of 20.3 fb−1 collected in 2012 by the ATLAS detector operating at the Large Hadron Collider. No events are observed in any of the signal regions, and limits are set on model parameters within supersymmetric scenarios involving R-parity violation, split supersymmetry, and gauge mediation. In some of the search channels, the trigger and search strategy are based only on the decay products of individual long-lived particles, irrespective of the rest of the event. In these cases, the provided limits can easily be reinterpreted in different scenarios.

Search for a heavy neutral particle decaying to eμ, eτ, or μτ in pp collisions at √s = 8 TeV with the ATLAS Detector

Mon 10 Dec 2018 12:03:23 KRAT

Search for long-lived, weakly interacting particles that decay to displaced hadronic jets in proton-proton collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:03:22 KRAT

A search for the decay of neutral, weakly interacting, long-lived particles using data collected by the ATLAS detector at the LHC is presented. This analysis uses the full data set recorded in 2012: 20.3 fb−1 of proton-proton collision data at √s = 8 TeV. The search employs techniques for reconstructing decay vertices of long-lived particles decaying to jets in the inner tracking detector and muon spectrometer. Signal events require at least two reconstructed vertices. No significant excess of events over the expected background is found, and limits as a function of proper lifetime are reported for the decay of the Higgs

Searches for Higgs boson pair production in the hh → bbττ, γγWW*, γγbb, bbbb channels with the ATLAS detector

Mon 10 Dec 2018 12:03:15 KRAT

We present the calculation of the hyperon forward spin polarizability γ0 using manifestly Lorentz-covariant baryon chiral perturbation theory including the intermediate contribution of the spin-3/2 states. As at the considered order the extraction of γ0 is a pure prediction of chiral perturbation theory, the obtained values are a good test for this theory. After including explicitly the decuplet states, our SU(2) results have a very good agreement with the experimental data and we extend our framework to SU(3) to give predictions for the hyperons’ γ0 values. Prominent are the Σ− and Ξ− baryons as their photon transition to the decuplet is forbidden in SU(3) symmetry and therefore they are not sensitive to the explicit inclusion of the decuplet in the theory.

Search for high-mass diphoton resonances in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:03:11 KRAT

This article describes a search for high-mass resonances decaying to a pair of photons using a sample of 20.3 fb−1 of pp collisions at √s = 8 TeV recorded with the ATLAS detector at the Large Hadron Collider. The data are found to be in agreement with the Standard Model prediction, and limits are reported in the framework of the Randall-Sundrum model. This theory leads to the prediction of graviton states, the lightest of which could be observed at the Large Hadron Collider. A lower limit of 2.66 (1.41) TeVat 95% confidence level is set on the mass of the lightest graviton for couplings of k=MPl ¼ 0.1 (0.01).

Search for Higgs and Z boson decays to J/ψγ and Υ(nS)γ with the ATLAS detector

Mon 10 Dec 2018 11:56:35 KRAT

A search for the decays of the Higgs and Z bosons to J=ψγ and ðnSÞγ (n ¼ 1; 2; 3) is performed with pp collision data samples corresponding to integrated luminosities of up to 20.3 fb−1 collected at pffisffiffi ¼ 8 TeV with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above expected backgrounds and 95% C.L. upper limits are placed on the branching fractions.

Search for new phenomena in dijet angular distributions in proton-proton collisions at √s = 8 TeV measured with the ATLAS detector

Mon 10 Dec 2018 11:56:34 KRAT

A search for new phenomena in LHC proton-proton collisions at a center-of-mass energy of √s=8 TeV was performed with the ATLAS detector using an integrated luminosity of 17.3 fb−1. The angular distributions are studied in events with at least two jets; the highest dijet mass observed is 5.5 TeV. All angular distributions are consistent with the predictions of the standard model. In a benchmark model of quark contact interactions, a compositeness scale below 8.1 TeV in a destructive interference scenario and 12.0 TeV in a constructive interference scenario is excluded at 95% C.L.; median expected limits are 8.9 TeV for the destructive interference scenario and 14.1 TeV for the constructive interference scenario.

Search for new phenomena in events with a photon and missing transverse momentum in pp collisions at √s=8 TeV with the ATLAS detector

Mon 10 Dec 2018 11:56:28 KRAT

Results of a search for new phenomena in events with an energetic photon and large missing transverse momentum with the ATLAS experiment at the LHC are reported. Data were collected in proton-proton collisions at a center-of-mass energy of 8 TeV and correspond to an integrated luminosity of 20.3 fb−1. The observed data are well described by the expected Standard Model backgrounds. The expected (observed) upper limit on the fiducial cross section for the production of events with a photon and large missing transverse momentum is 6.1 (5.3) fb at 95% confidence level. Exclusion limits are presented on models of new phenomena with large extra spatial dimensions, supersymmetric quarks, and direct pair production of dark-matter candidates.

Search for Higgs bosons decaying to aa in the μμττ final state in pp collisions at √s = 8 TeV with the ATLAS experiment

Mon 10 Dec 2018 11:56:24 KRAT

A search for the decay to a pair of new particles of either the 125 GeV Higgs boson (h) or a second charge parity (CP)-even Higgs boson (H) is presented. The data set corresponds to an integrated luminosity of 20.3 fb−1 of pp collisions at √s = 8 TeV recorded by the ATLAS experiment at the LHC in 2012. The search was done in the context of the next-to-minimal supersymmetric standard model, in which the new particles are the lightest neutral pseudoscalar Higgs bosons (a). One of the two a bosons is required to decay to two muons while the other is required to decay to two τ leptons. No significant excess is observed above the expected backgrounds in the dimuon invariant mass range from 3.7 to 50 GeV. Upper limits are placed on the production of h → aa relative to the standard model gg → h production, assuming no coupling of the a boson to quarks. The most stringent limit is placed at 3.5% for ma ¼ 3.75 GeV. Upper limits are also placed on the production cross section of H → aa from 2.33 to 0.72 pb, for fixed ma ¼ 5 GeV with mH ranging from 100 to 500 GeV.

Search for heavy long-lived multi-charged particles in pp collisions at √s = 8 TeV using the ATLAS detector

Mon 10 Dec 2018 11:56:22 KRAT

A search for heavy long-lived multi-charged particles is performed using the ATLAS detector at the LHC. Data collected in 2012 at s√=8 TeV from pp collisions corresponding to an integrated luminosity of 20.3 fb−1 are examined. Particles producing anomalously high ionisation, consistent with long-lived massive particles with electric charges from |q|=2e to |q|=6e are searched for. No signal candidate events are observed, and 95% confidence level cross-section upper limits are interpreted as lower mass limits for a Drell--Yan production model. The mass limits range between 660 and 785 GeV.

Search for low-scale gravity signatures in multi-jet final states with the ATLAS detector at √s = 8 TeV

Mon 10 Dec 2018 11:56:12 KRAT

A search for evidence of physics beyond the Standard Model in final states with multiple high-transverse-momentum jets is performed using 20.3 fb−1 of proton-proton collision data at ps = 8TeV recorded by the ATLAS detector at the LHC. No significant excess of events beyond Standard Model expectations is observed, and upper limits on the visible cross sections for non-Standard Model production of multi-jet final states are set. A wide variety of models for black hole and string ball production and decay are considered, and the upper limit on the cross section times acceptance is as low as 0.16 fb at the 95% confidence level. For these models, excluded regions are also given as function of the main model parameters.

Search for H→γγ produced in association with top quarks and constraints on the Yukawa coupling between the top quark and the Higgs boson using data taken at 7 TeV and 8 TeV with the ATLAS detector

Mon 10 Dec 2018 11:56:10 KRAT

A search is performed for Higgs bosons produced in association with top quarks using the diphoton decay mode of the Higgs boson. Selection requirements are optimized separately for leptonic and fully hadronic final states from the top quark decays. The dataset used corresponds to an integrated luminosity of 4.5fb−1of proton–proton collisions at a center-of-mass energy of 7TeV and 20.3fb−1at 8TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess over the background prediction is observed and upper limits are set on the t¯t H production cross section. The observed exclusion upper limit at 95% confidence level is 6.7times the predicted Standard Model cross section value. In addition, limits are set on the strength of the Yukawa coupling between the top quark and the Higgs boson, taking into account the dependence of the t¯tHand tHcross sections as well as the H→γγbranching fraction on the Yukawa coupling. Lower and upper limits at 95% confidence level are set at −1.3and +8.0times the Yukawa coupling strength in the Standard Model.

Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 11:56:05 KRAT

Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT >120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presented.

Search for charged Higgs bosons decaying via H ± → τ ± ν in fully hadronic final states using pp collision data at √s=8 TeV with the ATLAS detector

Mon 10 Dec 2018 11:49:15 KRAT

The results of a search for charged Higgs bosons decaying to a τ lepton and a neutrino, H± ! τ±ν, are presented. The analysis is based on 19.5 fb−1 of proton-proton collision data at √s=8 TeV collected by the ATLAS xperiment at the Large Hadron Collider. Charged Higgs bosons are searched for in events consistent with top-quark pair production or in associated production with a top quark, depending on the considered H± mass. The final state is characterised by the presence of a hadronic τ decay, missing transverse momentum, b-tagged jets, a hadronically decaying W boson, and the absence of any isolated electrons or muons with high transverse momenta. The data are consistent with the expected background from Standard Model processes. A statistical analysis leads to 95% confidence-level upper limits on the product of branching ratios B(t ! bH±) × B(H± ! τ±ν), between 0.23% and 1.3% for charged Higgs boson masses in the range 80–160GeV. It also leads to 95% confidence-level upper limits on the production cross section times branching

Search for heavy lepton resonances decaying to a Z boson and a lepton in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 11:49:15 KRAT

A search for heavy leptons decaying to a Z boson and an electron or a muon is presented. The search is based on pp collision data taken at s√=8 TeV by the ATLAS experiment at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb−1. Three high-transverse-momentum electrons or muons are selected, with two of them required to be consistent with originating from a Z boson decay. No significant excess above Standard Model background predictions is observed, and 95% confidence level limits on the production cross section of high-mass trilepton resonances are derived. The results are interpreted in the context of vector-like lepton and type-III seesaw models. For the vector-like lepton model, most heavy lepton mass values in the range 114-176 GeV are excluded. For the type-III seesaw model, most mass values in the range 100-468 GeV are excluded.

Search for anomalous production of prompt same-sign lepton pairs and pair-produced doubly charged Higgs bosons with √s=8 TeV pp collisions using the ATLAS detector

Mon 10 Dec 2018 11:42:24 KRAT

A low-background inclusive search for new physics in events with same-sign dileptons is presented. The search uses proton-proton collisions corresponding to 20.3 fb−1 of integrated luminosity taken in 2012 at a centre-of-mass energy of 8TeV with the ATLAS detector at the LHC. Pairs of isolated leptons with the same electric charge and large transverse momenta of the type e±e±, e±μ±, and μ±μ± are selected and their invariant mass distribution is examined. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the cross-sections for processes beyond the Standard Model. Limits are placed as a function of the dilepton invariant mass within a fiducial region corresponding to the signal event selection criteria. Exclusion limits are also derived for a specific model of doubly charged Higgs boson production.

Search for a charged Higgs boson produced in the vector-boson fusion mode with decay H± → W±Z using pp collisions at √s = 8 TeV with the ATLAS experiment

Mon 10 Dec 2018 11:42:19 KRAT

A search for a charged Higgs boson, H, decaying to aW boson and a Z boson is presented. The search is based on 20.3 fb−1 of proton-proton collision data at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. The H boson is assumed to be produced via vector-boson fusion and the decays W → qq¯0 and Z → eþe−=μþμ− are considered. The search is performed in a range of charged

Search for new light gauge bosons in Higgs boson decays to four-lepton final states in pp collisions at √s = 8 TeV with the ATLAS detector at the LHC

Mon 10 Dec 2018 11:35:11 KRAT

This paper presents a search for Higgs bosons decaying to four leptons, either electrons or muons, via one or two light exotic gauge bosons Zd, H→ZZd→4ℓ or H→ZdZd→4ℓ. The search was performed using pp collision data corresponding to an integrated luminosity of about 20 fb−1 at the center-of-mass energy of s√=8 TeV recorded with the ATLAS detector at the Large Hadron Collider. The observed data are well described by the Standard Model prediction. Upper bounds on the branching ratio of H→ZZd→4ℓ and on the kinetic mixing parameter between the Zd and the Standard Model hypercharge gauge boson are set in the range (1–9)×10−5 and (4–17)×10−2 respectively, at 95% confidence level assuming the Standard Model branching ratio of H→ZZ∗→4ℓ, for Zd masses between 15 and 55 GeV. Upper bounds on the effective mass mixing parameter between the Z and the Zd are also set using the branching ratio limits in the H→ZZd→4ℓ search, and are in the range (1.5–8.7)×10−4 for 15

Search for direct pair production of a chargino and a neutralino decaying to the 125 GeV Higgs boson in √s=8 TeV pp collisions with the ATLAS detector

Mon 10 Dec 2018 11:35:09 KRAT

A search is presented for the direct pair production of a chargino and a neutralino pp → ˜χ±1 χ˜ 02 , where the chargino decaysto the lightest neutralino and the W boson, χ˜ ±1 → ˜χ01 (W± → ±ν), while the neutralino decays to the lightest neutralino and the 125 GeV Higgs boson,χ˜ 02 → ˜χ01 (h → bb/γ γ /±νqq). The final states considered for the search have large missing transverse momentum, an isolated electron or muon, and one of the following: either two jets identified as originating from bottom quarks, or two photons, or a second electron or muon with the same electric charge. The analysis is based on 20.3 fb−1 of √s = 8 TeV proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with the Standard Model expectations, and limits are set in the context of a simplified supersymmetric model

Differential top-antitop cross-section measurements as a function of observables constructed from final-state particles using pp collisions at √s=7 TeV in the ATLAS detector

Mon 03 Dec 2018 15:39:38 KRAT

Various differential cross-sections are measured in top-quark pair (t¯t) events produced in proton-proton collisions at a centre-of-mass energy of √s = 7TeV at the LHC with the ATLAS detector. These differential cross-sections are presented in a data set corresponding to an integrated luminosity of 4.6 fb−1. The differential cross-sections are presented in terms of kinematic variables, such as momentum, rapidity and invariant mass, of a top-quark proxy referred to as the pseudo-top-quark as well as the pseudo-top-quark pair system. The dependence of the measurement on theoretical models is minimal. The measurements are performed on t¯t events in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of them tagged as originating from a b-quark. The hadronic and leptonic pseudo-top-quarks are defined via the leptonic or hadronic decay mode of the W boson produced by the top-quark decay in events with a single charged lepton. Differential cross-section measurements of the pseudo-top-quark variables are compared with several Monte Carlo models that implement next-to-leading order or leading-order multi-leg matrix-element calculation

Evidence for the Higgs-boson Yukawa coupling to tau leptons with the ATLAS detector

Mon 03 Dec 2018 15:25:38 KRAT

Results of a search for H → τ τ decays are presented, based on the full set of proton-proton collision data recorded by the ATLAS experiment at the LHC during 2011 and 2012. The data correspond to integrated luminosities of 4.5 fb−1 and 20.3 fb−1 at centre-of-mass energies of √ s = 7 TeV and √ s = 8 TeV respectively. All combinations of leptonic (τ → `νν¯ with ` = e, µ) and hadronic (τ → hadrons ν) tau decays are considered. An excess of events over the expected background from other Standard Model processes is found with an observed (expected) significance of 4.5 (3.4) standard deviations. This excess provides evidence for the direct coupling of the recently discovered Higgs boson to fermions. The measured signal strength, normalised to the Standard Model expectation, of µ = 1.43 +0.43 −0.37 is consistent with the predicted Yukawa coupling strength in the Standard Model.

Centrality and rapidity dependence of inclusive jet production in √sNN = 5.02 TeV proton-lead collisions with the ATLAS detector

Mon 03 Dec 2018 12:30:39 KRAT

Measurements of the centrality and rapidity dependence of inclusive jet production in √sNN=5.02TeV proton–lead (p +Pb) collisions and the jet cross-section in √s=2.76TeV proton–proton collisions are presented. These quantities are measured in datasets corresponding to an integrated luminosity of 27.8nb−1and 4.0pb−1, respectively, recorded with the ATLAS detector at the Large Hadron Collider in2013. The p +Pbcollision centrality was characterised using the total transverse energy measured in the pseudorapidity interval −4.9 <η<−3.2in the direction of the lead beam. Results are presented for the double-differential per-collision yields as a function of jet rapidity and transverse momentum (pT) for minimum-bias and centrality-selected p +Pbcollisions, and are compared to the jet rate from the geometric expectation. The total jet yield in minimum-bias events is slightly enhanced above the expectation in a pT-dependent manner but is consistent with the expectation within uncertainties. The ratios of jet spectra from different centrality selections show a strong modification of jet production at all pTat forward rapidities and for large pTat mid-rapidity, which manifests as a suppression of the jet yield in central events and an enhancement in peripheral events. These effects imply that the factorisation between hard and soft processes is violated at an unexpected level in proton–nucleus collisions. Furthermore, the modifications at forward rapidities are found to be a function of the total jet energy only, implying that the violations may have a simple dependence on the hard parton–parton kinematics.

Analysis of events with b-jets and a pair of leptons of the same charge in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 03 Dec 2018 11:55:39 KRAT

An analysis is presented of events containing jets including at least one b-tagged jet, sizeable missing transverse momentum, and at least two leptons including a pair of the same electric charge, with the scalar sum of the jet and lepton transverse momenta being large. A data sample with an integrated luminosity of 20.3 fb−1 of pp collisions at √s=8 TeV recorded by the ATLAS detector at the Large Hadron Collider is used. Standard Model processes rarely produce these final states, but there are several models of physics beyond the Standard Model that predict an enhanced rate of production of such events; the ones considered here are production of vector-like quarks, enhanced four-top-quark production, pair production of chiral b′-quarks, and production of two positively charged top quarks. Eleven signal regions are defined; subsets of these regions are combined when searching for each class of models. In the three signal regions primarily sensitive to positively charged top quark pair production, the data yield is consistent with the background expectation. There are more data events than expected from background in the set of eight signal regions defined for searching for vector-like quarks and chiral b′-quarks, but the significance of the discrepancy is less than two standard deviations. The discrepancy reaches 2.5 standard deviations in the set of five signal regions defined for searching for four-top-quark production. The results are used to set 95% CL limits on various models.

A search for high-mass resonances decaying to τ+τ- in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 03 Dec 2018 11:13:38 KRAT

A search for high-mass resonances decaying into τ+τ − final states using proton proton collisions at √s = 8 TeV produced by the Large Hadron Collider is presented. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 19.5–20.3 fb−1. No statistically significant excess above the Standard Model expectation is observed; 95% credibility upper limits are set on the cross section times branching fraction of Z0 resonances decaying into τ+τ − pairs as a function of the resonance mass. As a result, Z0 bosons of the Sequential Standard Model with masses less than 2.02 TeV are excluded at 95% credibility. The impact of the fermionic couplings on the Z0 acceptance is investigated and limits are also placed on a Z0 model that exhibits enhanced couplings to third-generation fermions.

Determination of spin and parity of the Higgs boson in the WW∗→eνμν decay channel with the ATLAS detector

Mon 03 Dec 2018 10:45:41 KRAT

Studies of the spin and parity quantum numbers of the Higgs boson in the W W∗ →eνμν final state are presented, based on proton–proton collision data collected by theATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb−1 at a centre-of-mass energy of √s = 8 TeV. The Standard Model spinparity JC P = 0++ hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the Standard-Model-like Higgs boson and CP-even (JC P = 0++) or CP-odd (JC P = 0+−)Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios.

Determination of the top-quark pole mass using t t¯ + 1-jet events collected with the ATLAS experiment in 7 TeV pp collisions

Mon 03 Dec 2018 10:45:41 KRAT

The normalized differential cross section for top-quark pair production in association with at least one jet is studied as a function of the inverse of the invariant mass of the tt¯+1-jet system. This distribution can be used for a precise determination of the top-quark mass since gluon radiation depends on the mass of the quarks. The experimental analysis is based on proton-proton collision data collected by the ATLAS detector at the LHC with a centre-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.6 fb−1. The selected events were identified using the lepton+jets top-quark-pair decay channel, where lepton refers to either an electron or a muon. The observed distribution is compared to a theoretical prediction at next-to-leading-order accuracy in quantum chromodynamics using the pole-mass scheme. With this method, the measured value of the top-quark pole mass, mpolet, is: mpolet =173.7 ± 1.5 (stat.) ± 1.4 (syst.) +1.0−0.5 (theory) GeV. This result represents the most precise measurement of the top-quark pole mass to date.

Determination of the ratio of b-quark fragmentation fractions fs/fd in pp collisions at √s = 7 TeV with the ATLAS detector

Mon 03 Dec 2018 10:45:38 KRAT

With an integrated luminosity of 2.47 fb−1 recorded by the ATLAS experiment at the LHC, the exclusive decays B0s→J/ψϕ and B0d→J/ψK*0 of B mesons produced in pp collisions at s√=7 TeV are used to determine the ratio of fragmentation fractions fs/fd. From the observed B0s→J/ψϕ and B0d→J/ψK*0 yields, the quantity (fs/fd)[B(B0s→J/ψϕ)/B(B0d→J/ψK*0)] is measured to be 0.199±0.004(stat)±0.008(syst). Using a recent theory prediction for [B(B0s→J/ψϕ)/B(B0d→J/ψK*0)] yields (fs/fd)=0.240±0.004(stat)±0.010(syst)±0.017(th). This result is based on a new approach that provides a significant improvement of the world average.

Constraints on the off-shell Higgs boson signal strength in the high-mass ZZ and WW final states with the ATLAS detector

Mon 03 Dec 2018 10:31:42 KRAT

Measurements of the ZZ and WW final states in the mass range above the 2mZ and 2mW thresholds provide a unique opportunity to measure the off-shell coupling strength of the Higgs boson. This paper presents constraints on the off-shell Higgs boson event yields normalised to the Standard Model prediction (signal strength) in the ZZ→4ℓ, ZZ→2ℓ2ν and WW→eνμν final states. The result is based on pp collision data collected by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 20.3 fb-1 at a collision energy of s√=8 TeV. Using the CLs method, the observed 95% confidence level (CL) upper limit on the off-shell signal strength is in the range 5.1-8.6, with an expected range of 6.7-11.0. In each case the range is determined by varying the unknown gg→ZZ and gg→WW background K-factor from higher-order QCD corrections between half and twice the value of the known signal K-factor. Assuming the relevant Higgs boson couplings are independent of the energy scale of the Higgs production, a combination with the on-shell measurements yields an observed (expected) 95% CL upper limit on ΓH/ΓSMH in the range 4.5- -7.5 (6.5- -11.2) using the same variations of the background K-factor. Assuming that the unknown gg→VV background K-factor is equal to the signal K-factor,this translates into an observed (expected) 95% CL upper limit on the Higgs boson total width of 22.7 (33.0) MeV.

Constraints on new phenomena via Higgs boson couplings and invisible decays with the ATLAS detector

Mon 03 Dec 2018 10:31:41 KRAT

The ATLAS experiment at the LHC has measured the Higgs boson couplings and mass, and searched for invisible Higgs boson decays, using multiple production and decay channels with up to 4.7 fb−1 of pp collision data at s√=7 TeV and 20.3 fb−1 at s√=8 TeV. In the current study, the measured production and decay rates of the observed Higgs boson in the γγ, ZZ, WW, Zγ, bb, ττ, and μμ decay channels, along with results from the associated production of a Higgs boson with a top-quark pair, are used to probe the scaling of the couplings with mass. Limits are set on parameters in extensions of the Standard Model including a composite Higgs boson, an additional electroweak singlet, and two-Higgs-doublet models. Together with the measured mass of the scalar Higgs boson in the γγ and ZZ decay modes, a lower limit is set on the pseudoscalar Higgs boson mass of mA>370 GeV in the "hMSSM" simplified Minimal Supersymmetric Standard Model. Results from direct searches for heavy Higgs bosons are also interpreted in the hMSSM. Direct searches for invisible Higgs boson decays in the vector-boson fusion and associated production of a Higgs boson with W/Z (Z→ll, W/Z→jj) modes are statistically combined to set an upper limit on the Higgs boson invisible branching ratio of 0.25. The use of the measured visible decay rates in a more general coupling fit improves the upper limit to 0.23, constraining a Higgs portal model of dark matter.

Combined measurement of the Higgs boson mass in pp collisions at √s = 7 and 8 TeV with the ATLAS and CMS experiments

Mon 03 Dec 2018 10:17:41 KRAT

A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H → γγ and H → ZZ → 4l decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is mH ¼ 125.09 0.21 ðstatÞ 0.11 ðsystÞ GeV.

Search for vectorlike B quarks in events with one isolated lepton, missing transverse momentum, and jets at √s = 8 TeV with the ATLAS detector

Mon 01 Jul 2019 12:51:35 KRAT

A search has been performed for pair production of heavy vectorlike down-type (B) quarks. The analysis explores the lepton-plus-jets final state, characterized by events with one isolated charged lepton (electron or muon), significant missing transverse momentum, and multiple jets. One or more

Search for flavour-changing neutral current top quark decays t → Hq in pp collisions at √s = 8 TeV with the ATLAS detector

Fri 11 May 2018 15:41:27 KRAT

A search for flavour-changing neutral current decays of a top quark to an uptype quark (q = u, c) and the Standard Model Higgs boson, where the Higgs boson decays to bb¯¯ , is presented. The analysis searches for top quark pair events in which one top quark decays to Wb, with the W boson decaying leptonically, and the other top quark decays to Hq. The search is based on pp collisions at s√=8 TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider and uses an integrated luminosity of 20.3 fb−1. Data are analysed in the lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of b-quark jets characteristic of signal events, and employs a likelihood discriminant that uses the kinematic differences between the signal and the background, which is dominated by tt¯→WbWb decays. No significant excess of events above the background expectation is found, and observed (expected) 95% CL upper limits of 0.56% (0.42%) and 0.61% (0.64%) are derived for the t → Hc and t → Hu branching ratios respectively. The combination of this search with other ATLAS searches in the H → γγ and H → WW *, ττ decay modes significantly improves the sensitivity, yielding observed (expected) 95% CL upper limits on the t → Hc and t → Hu branching ratios of 0.46% (0.25%) and 0.45% (0.29%) respectively. The corresponding combined observed (expected) upper limits on the |λ tcH | and |λ tuH | couplings are 0.13 (0.10) and 0.13 (0.10) respectively. These are the most restrictive direct bounds on tqH interactions measured so far.

Measurements of the top quark branching ratios into channels with leptons and quarks with the ATLAS detector

Fri 11 May 2018 15:41:20 KRAT

Measurements of the branching ratios of top quark decays into leptons and jets using events with t¯t (top antitop) pairs are reported. Events were recorded with the ATLAS detector at the LHC in pp collisions at a center-of-mass energy of 7 TeV. The collected data sample corresponds to an integrated luminosity of 4.6 fb−1. The measured top quark branching ratios agree with the Standard Model predictions within the measurement uncertainties of a few percent.

Search for metastable heavy charged particles with large ionisation energy loss in pp collisions at √s = 8 TeV using the ATLAS experiment

Fri 11 May 2018 15:41:20 KRAT

Many extensions of the Standard Model predict the existence of charged heavy long-lived particles, such as R-hadrons or charginos. These particles, if produced at the Large Hadron Collider, should be moving non-relativistically and are therefore identifiable through the measurement of an anomalously large specific energy loss in the ATLAS pixel detector. Measuring heavy long-lived particles through their track parameters in the vicinity of the interaction vertex provides sensitivity to metastable particles with lifetimes from 0.6 ns to 30 ns. A search for such particles with the ATLAS detector at the Large Hadron Collider is presented, based on a data sample corresponding to an integrated luminosity of 18.4 fb −1 of pp collisions at s√=8 TeV. No significant deviation from the Standard Model background expectation is observed, and lifetime-dependent upper limits on R-hadrons and chargino production are set. Gluino R-hadrons with 10 ns lifetime and masses up to 1185 GeV are excluded at 95 % confidence level, and so are charginos with 15 ns lifetime and masses up to 482 GeV.

Search for pair production of a new heavy quark that decays into a W boson and a light quark in pp collisions at √s = 8 TeV with the ATLAS detector

Fri 11 May 2018 12:47:05 KRAT

A search is presented for pair production of a new heavy quark (Q) that decays into a W boson and a light quark (q) in the final state where one W boson decays leptonically (to an electron or muon plus a neutrino) and the other W boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb−1 of pp collisions at √s = 8 TeV collected by the ATLAS detector at the LHC. No evidence of QQ¯ production is observed. New chiral quarks with masses below 690 GeV are excluded at 95% confidence level, assuming BR(Q→Wq) = 1. Results are also interpreted in the context of vectorlike quark models, resulting in the limits on the mass of a vectorlike quark in the two-dimensional plane of BR(Q→Wq) versus BR(Q→Hq) .

Measurement of four-jet differential cross sections in √s = 8 TeV proton-proton collisions using the ATLAS detector

Fri 11 May 2018 12:46:56 KRAT

Differential cross sections for the production of at least four jets have been measured in proton-proton collisions at sqrt{s}=8 TeV at the Large Hadron Collider using the ATLAS detector. Events are selected if the four anti-k t R = 0.4 jets with the largest transverse momentum (p T) within the rapidity range |y| < 2.8 are well separated (ΔR 4j min > 0.65), all have p T > 64 GeV, and include at least one jet with p T > 100 GeV. The dataset corresponds to an integrated luminosity of 20.3 fb−1 . The cross sections, corrected for detector effects, are compared to leading-order and next-to-leading-order calculations as a function of the jet momenta, invariant masses, minimum and maximum opening angles and other kinematic variables.

Search for lepton-flavour-violating H → μτ decays of the Higgs boson with the ATLAS detector

Fri 07 Dec 2018 10:40:45 KRAT

A direct search for lepton-flavour-violating H → μτ decays of the recently discovered Higgs boson with the ATLAS detector at the LHC is presented. The analysis is performed in the H → μτ had channel, where τ had is a hadronically decaying τ -lepton. The search is based on the data sample of proton-proton collisions collected by the ATLAS experiment corresponding to an integrated luminosity of 20.3 fb−1 at a centre-of-mass energy of s√=8s=8 TeV. No statistically significant excess of data over the predicted background is observed. The observed (expected) 95% confidence-level upper limit on the branching fraction, Br(H → μτ ), is 1.85% (1.24%).

Search for heavy Majorana neutrinos with the ATLAS detector in pp collisions at √8 = 8 TeV

Fri 07 Dec 2018 10:40:07 KRAT

A search for heavy Majorana neutrinos in events containing a pair of high-pT leptons of the same charge and high-pT jets is presented. The search uses 20.3 fb−1 of pp collision data collected with the ATLAS detector at the CERN Large Hadron Collider with a centre-of-mass energy of ps = 8TeV. The data are found to be consistent with the

Search for invisible particles produced in association with single-top-quarks in proton–proton collisions at √ s = 8 TeV with the ATLAS detector

Fri 07 Dec 2018 10:33:42 KRAT

A search for the production of single-top-quarks in association with missing energy is performed in proton–proton collisions at a centre-of-mass energy of √s = 8 TeV with the ATLASexperiment at the large hadron collider using data collected in 2012, corresponding to an integrated luminosity of 20.3 fb−1. In this search, the W boson from the top quark is required to decay into an electron or a muon and a neutrino. No deviation from the standard model prediction is observed, and upper limits are set on the production cross-section for resonant and non-resonant production of an invisible exotic state in association with a right-handed top quark. In the case of resonant production, for a spin-0 resonance with amass of 500 GeV, an effective coupling strength above 0.15 is excluded at 95% confidence level for the top quark and an invisible spin-1/2 state with mass between 0 and 100 GeV. In the case of non-resonant production, an effective coupling strength above 0.2 is excluded at 95% confidence level for the top quark and an invisible spin-1 state with mass between 0 and 657 GeV.

Search for dark matter in events with missing transverse momentum and a Higgs boson decaying to two photons in pp collisions at √s = 8 TeV with the ATLAS detector

Fri 07 Dec 2018 10:33:35 KRAT

Results of a search for new phenomena in events with large missing transverse momentum and a Higgs boson decaying to two photons are reported. Data from proton-proton collisions at a center-of-mass energy of 8 TeV and corresponding to an integrated luminosity of 20.3 fb−1 have been collected with the ATLAS detector at the LHC. The observed data are well described by the expected standard model backgrounds. Upper limits on the cross section of events with large missing transverse momentum and a Higgs boson candidate are also placed. Exclusion limits are presented for models of physics beyond the standard model featuring dark-matter candidates.

Search for dark matter in events with heavy quarks and missing transverse momentum in pp collisions with the ATLAS detector

Fri 07 Dec 2018 10:33:13 KRAT

This article reports on a search for dark matter pair production in association with bottom or top quarks in 20.3 fb−1 of pp collisions collected at √s = 8 TeV by the ATLAS detector at the LHC. Eventswith largemissing transverse momentum are selected when produced in association with high-momentum jets of which one or more are identified as jets containing b-quarks. Final states with top quarks are selected by requiring a high jet multiplicity and in some cases a single lepton. The data are found to be consistent with the Standard Model expectations and limits are set on the mass scale of effective field theories that describe scalar and tensor interactions between dark matter and Standard Model particles. Limits on the dark-matter–nucleon cross-section for spin-independent and spin-dependent interactions are also provided. These limits are particularly strong for low-mass dark matter. Using a simplified model, constraints are set on the mass of dark matter and of a coloured mediator suitable to explain a possible signal of annihilating dark matter.

Search for massive supersymmetric particles decaying to many jets using the ATLAS detector in pp collisions at √s = 8 TeV

Fri 07 Dec 2018 10:26:19 KRAT

Results of a search for decays of massive particles to fully hadronic final states are presented. This search uses 20.3 fb−1 of data collected by the ATLAS detector in √s = 8 TeV proton-proton collisions at the LHC. Signatures based on high jet multiplicities without requirements on the missing transverse momentum are used to search for R-parity-violating supersymmetric gluino pair production with subsequent decays to quarks. The analysis is performed using a requirement on the number of jets, in combination with separate requirements on the number of b-tagged jets, as well as a topological observable formed from the scalar sum of the mass values of large-radius jets in the event. Results are interpreted in the context of all possible branching ratios of direct gluino decays to various quark flavors. No significant deviation is observed from the expected Standard Model backgrounds estimated using jet counting as well as data-driven templates of the total-jet-mass spectra. Gluino pair decays to ten or more quarks via intermediate neutralinos are excluded for a gluino with mass m~g < 1 TeV for a neutralino mass m~χ0 1 ¼ 500 GeV. Direct gluino decays to six quarks are excluded for m~g < 917 GeV for light-flavor final states, and results for various flavor hypotheses are presented.

Measurements of the W production cross sections in association with jets with the ATLAS detector

Fri 07 Dec 2018 10:26:15 KRAT

This paper presents cross sections for the production of a W boson in association with jets, measured in proton–proton collisions at √s = 7 TeV with the ATLAS experiment at the large hadron collider. With an integrated uminosity of 4.6 fb−1, this data set allows for an exploration of a large kinematic range, including jet production up to a transverse momentum of 1 TeV and multiplicities up to seven associated jets. The production cross sections for W bosons are measured in both the electron and muon decay channels. Differential cross sections formany observables are also presented including measurements of the jet observables such as the rapidities and the transverse momenta as well as measurements of event observables such as the scalar sums of the transverse momenta of the jets. The measurements are compared to numerous QCD predictions including next-toleading-order perturbative calculations, resummation calculations and Monte Carlo generators.

Search for Higgs boson pair production in the γγbb¯ final state using pp collision data at √s=8 TeV from the ATLAS detector

Fri 07 Dec 2018 10:26:14 KRAT

Searches are performed for resonant and nonresonant Higgs boson pair production in the γγbb¯ final state using 20 fb−1 of proton-proton collisions at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the CERN Large Hadron Collider. A 95% confidence level upper limit on the cross section times branching ratio of nonresonant production is set at 2.2 pb, while the expected limit is 1.0 pb. The difference derives from a modest excess of events, corresponding to 2.4 standard deviations from the background-only hypothesis. The limit observed in the search for a narrow X→hh resonance ranges between 0.7 and 3.5 pb as a function of the resonance mass.

Search for invisible decays of the Higgs boson produced in association with a hadronically decaying vector boson in pp collisions at √s=8 TeV with the ATLAS detector

Fri 07 Dec 2018 10:26:12 KRAT

A search for Higgs boson decays to invisible particles is performed using 20.3 fb−1 of pp collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The process considered is Higgs boson production in association with a vector boson (V = W or Z) that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain V H production followed by H decaying to invisible particles for the Higgs boson mass range 115 < mH < 300 GeV. The 95%confidence-level observed upper limit on σV H × BR(H → inv.) varies from 1.6 pb at 115 GeV to 0.13 pb at 300 GeV. Assuming Standard Model production and including the gg → H contribution as signal, the results also lead to an observed upper limit of 78%at 95%confidence level on the branching ratio of Higgs bosons decays to invisible particles at a mass of 125 GeV.

Measurements of the total and differential Higgs boson production cross sections combining the H → γγ and H → ZZ* → 4ℓ decay channels at √s = 8 TeV with the ATLAS detector

Fri 07 Dec 2018 10:19:10 KRAT

Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3 fb-1 of pp collisions produced by the Large Hadron Collider at a center-of-mass energy of yjs = 8 TeV and recorded by the ATLAS detector. Cross sections are obtained from measured H ^ yy and H ^ ZZ* ^ 41 event yields, which are combined accounting for detector efficiencies, fiducial acceptances, and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be ffpp^H = 33.0 ± 5.3 (stat) ± 1.6 (syst) pb. The measurements are compared to state-of-the-art predictions.

Measurements of Higgs boson production and couplings in the four-lepton channel in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector

Fri 07 Dec 2018 10:19:05 KRAT

The final ATLAS Run 1 measurements of Higgs boson production and couplings in the decay channel H → ZZ → lþl−l0þl0−, where l, l0 ¼ e or μ, are presented. These measurements were performed using pp collision data corresponding to integrated luminosities of 4.5 and 20.3 fb−1 at center-of-mass energies of 7 and 8 TeV, respectively, recorded with the ATLAS detector at the LHC. The H → ZZ → 4l signal is