Observation of an excited Bc± meson state with the ATLAS detector

Wed 12 Dec 2018 18:20:24 KRAT

A search for excited states of the Bf meson is performed using 4.9 fb-1 of 7 TeVand 19.2 fb-1 of 8 TeV pp collision data collected by the ATLAS experiment at the LHC. A new state is observed through its hadronic transition to the ground state, with the latter detected in the decay Bf ^ J/ynf. The state appears in the m(Bfn+n—) — m(Bf) — 2m(nf) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842 f 4 f 5 MeV, where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S-wave state of the Bf meson, Bf (2S).

Measurement of differential production cross-sections for a Z boson in association with b-jets in 7 TeV proton-proton collisions with the ATLAS detector

Wed 12 Dec 2018 16:45:25 KRAT

Measurements of differential production cross-sections of a Z boson in association with b-jets in pp collisions at ps = 7TeV are reported. The data analysed correspond to an integrated luminosity of 4.6 fb−1 recorded with the ATLAS detector at the Large Hadron Collider. Particle-level cross-sections are determined for events with a Z boson decaying into an electron or muon pair, and containing b-jets. For events with at least one b-jet, the cross-section is presented as a function of the Z boson transverse momentum and rapidity, together with the inclusive b-jet cross-section as a function of b-jet transverse momentum, rapidity and angular separations between the b-jet and the Z boson. For events with at least two b-jets, the cross-section is determined as a function of the invariant mass and angular separation of the two highest transverse momentum b-jets, and as a function of the Z boson transverse momentum and rapidity. Results are compared to leading-order and next-to-leading-order perturbative QCD calculations.

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.

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

Measurement of the absolute branching fraction for Λc+ → Λe+νe

Wed 05 Dec 2018 10:08:21 KRAT

We report the first measurement of the absolute branching fraction for Λ+c→Λe+νe. This measurement is based on 567 pb−1 of e+e− annihilation data produced at s√=4.599 GeV, which is just above the Λ+cΛ¯−c threshold. The data were collected with the BESIII detector at the BEPCII storage rings. The branching fraction is determined to be B(Λ+c→Λe+νe)=[3.63±0.38(stat)±0.20(syst)]%, representing a significant improvement in precision over the current indirect determination. As the branching fraction for Λ+c→Λe+νe is the benchmark for those of other Λ+c semileptonic channels, our result provides a unique test of different theoretical models, which is the most stringent to date.

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 branching fractions of Ds+→η'X and Ds+→η'ρ+ in e+e-→Ds+Ds-

Wed 05 Dec 2018 10:08:08 KRAT

We study D+s decays to final states involving the η with a 482 pb−1 data sample collected at √s = 4.009 GeV with the BESIII detector at the BEPCII collider. We measure the branching fractionsB(D+s →η X) = (8.8 ± 1.8 ± 0.5)% and B(D+s →ηρ+) = (5.8 ± 1.4 ± 0.4)% where the first uncertainty is statistical and the second is systematic. In addition, we estimate an upper limit on the non-resonant branching ratio B(D+s →ηπ+π0) < 5.1% at the 90% confidence level. Our results are consistent with CLEO’s recent measurements and help to resolve the disagreement between the theoretical prediction and CLEO’s previous measurement of B(D+s →ηρ+).

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 the proton form factor by studying e+e- → pp¯

Wed 05 Dec 2018 09:54:11 KRAT

Using data samples collected with the BESIII detector at the BEPCII collider, we measure the Born cross section of e+e−→pp¯ at 12 center-of-mass energies from 2232.4 to 3671.0 MeV. The corresponding effective electromagnetic form factor of the proton is deduced under the assumption that the electric and magnetic form factors are equal (|GE|=|GM|). In addition, the ratio of electric to magnetic form factors, |GE/GM|, and |GM| are extracted by fitting the polar angle distribution of the proton for the data samples with larger statistics, namely at s√=2232.4 and 2400.0 MeV and a combined sample at s√=3050.0, 3060.0 and 3080.0 MeV, respectively. The measured cross sections are in agreement with recent results from BABAR, improving the overall uncertainty by about 30%. The |GE/GM| ratios are close to unity and consistent with BABAR results in the same q2 region, which indicates the data are consistent with the assumption that |GE|=|GM| within uncertainties.

Measurement of the energy resolution and calibration of hybrid pixel detectors with GaAs:Cr sensor and Timepix readout chip

Wed 05 Dec 2018 09:54:06 KRAT

This paper describes an iterative method of per-pixel energy calibration of hybrid pixel detectors with GaAs:Cr sensor and Timepix readout chip. A convolution of precisely measured spectra of characteristic X-rays of different metals with the resolution and the efficiency of the pixel detector is used for the calibration. The energy resolution of the detector is also measured during the calibration. The use of per-pixel calibration allows to achieve a good energy resolution of the Timepix detector with GaAs:Cr sensor: 8 and 13% at 60 and 20 keV, respectively.

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 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 B(ψ (3770) → γχc1) and search for ψ (3770) → γχc2

Wed 05 Dec 2018 09:40:13 KRAT

We report a measurement of the branching fraction for ψ(3770)→γχc1 and search for the transition ψ(3770)→γχc2 based on 2.92 fb−1 of e+e− data accumulated at s√=3.773 GeV with the BESIII detector at the BEPCII collider. We measure B(ψ(3770)→γχc1)=(2.48±0.15±0.23)×10−3, which is the most precise measurement to date. The upper limit on the branching fraction of ψ(3770)→γχc2 at a 90% confidence level is B(ψ(3770)→γχc2)<0.64×10−3. The corresponding partial widths are Γ(ψ(3770)→γχc1)=(67.5±4.1±6.7) keV and Γ(ψ(3770)→γχc2)<17.4 keV.

Measurement of the e+e- → ηJ/ψ cross section and search for e+e- → π0J/ψ at center-of-mass energies between 3.810 and 4.600 GeV

Wed 05 Dec 2018 09:40:08 KRAT

Using data samples collected with the BESIII detector operating at the BEPCII collider at 17 center-of-mass energies from 3.810 to 4.600 GeV, we perform a study of e+e−→ηJ/ψ and π0J/ψ. The Born cross sections of these two processes are measured at each center-of-mass energy. The measured energy-dependent Born cross section for e+e−→ηJ/ψ shows an enhancement around 4.2 GeV. The measurement is compatible with an earlier measurement by Belle.

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 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.

Measurement of the form factors in the decay D+ → ωe+νe and search for the decay D+→ϕe+νe

Tue 04 Dec 2018 10:12:42 KRAT

Using 2.92 fb−1 of electron-positron annihilation data collected at a center-of-mass energy of s√=3.773 GeV with the BESIII detector, we present an improved measurement of the branching fraction B(D+→ωe+νe)=(1.63±0.11±0.08)×10−3. The parameters defining the corresponding hadronic form factor ratios at zero momentum transfer are determined for the first time; we measure them to be rV=1.24±0.09±0.06 and r2=1.06±0.15±0.05. The first and second uncertainties are statistical and systematic, respectively. We also search for the decay D+→ϕe+νe. An improved upper limit B(D+→ϕe+νe)<1.3×10−5 is set at 90% confidence level.

Measurement of the matrix elements for the decays η →π+π-π0 and η/η′ →π0π0π0

Tue 04 Dec 2018 10:12:39 KRAT

Based on a sample of 1.31×109 J/ψ events collected with the BESIII detector at the BEPCII collider, Dalitz plot analyses of selected 79,625 η→π+π−π0 events, 33,908 η→π0π0π0 events, and 1,888 η′→π0π0π0 events are performed. The measured matrix elements of η→π+π−π0 are in reasonable agreement with previous measurements. The Dalitz plot slope parameters of η→π0π0π0 and η′→π0π0π0 are determined to be −0.055±0.014±0.004 and −0.640±0.046±0.047, respectively, where the first uncertainties are statistical and the second systematic. Both values are consistent with previous measurements, while the precision of the latter one is improved by a factor of 3. Final state interactions are found to have an important role in those decays.

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.

Evidence for in e+e- → γχc1,2 at center-of-mass energies from 4.009 to 4.360 GeV

Tue 04 Dec 2018 09:44:45 KRAT

Using data samples collected at center-of-mass energies of √s=4.009, 4.230, 4.260, and 4.360 GeV with the BESIII detector operating at the BEPCII collider, we perform a search for the process e+e−→γχcJ (J=0, 1, 2)and find evidence for e+e−→γχc1 and e+e−→γχc2 with statistical significances of 3.0σ and 3.4σ, respectively. The Born cross sections σB(e+e−→γχcJ ), as well as their upper limits at the 90% confidence level (C.L.) are determined

Observation and Spin-Parity Determination of the X(1835) in J/ψ →γ K0SK0Sη

Thu 06 Dec 2018 14:08:06 KRAT

We report an observation of the process J/ψ→γX(1835)→γK0SK0Sη at low K0SK0S mass with a statistical significance larger than 12.9σ using a data sample of 1.31×109 J/ψ events collected with the BESIII detector. In this region of phase space the K0SK0S system is dominantly produced through the f0(980). By performing a partial wave analysis, we determine the spin parity of the X(1835) to be JPC=0−+. The mass and width of the observed X(1835) are 1844±9(stat)+16−25(syst) MeV/c2 and 192+20−17(stat)+62−43(syst) MeV, respectively, which are consistent with the results obtained by BESIII in the channel J/ψ→γπ+π−η′.

Observation of the Dalitz decay η' → γe+e-

Thu 06 Dec 2018 13:33:18 KRAT

We report the first observation of the Dalitz decay η′→γe+e−, based on a data sample of 1.31 billion J/ψ events collected with the BESIII detector. The η′ mesons are produced via the J/ψ→γη′ decay process. The ratio Γ(η′→γe+e−)/Γ(η′→γγ) is measured to be (2.13±0.09(stat)±0.07(sys))×10−2. This corresponds to a branching fraction B(η′→γe+e−)=(4.69±0.20(stat)±0.23(sys))×10−4. The transition form factor is extracted and different expressions are compared to the measured dependence on the e+e− invariant mass. The results are consistent with the prediction of the vector meson dominance model.

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 of the electromagnetic doubly OZI-suppressed decay J/ψ → фπ0

Thu 06 Dec 2018 11:27:20 KRAT

Using a sample of 1.31 billion J/ψ events accumulated with the BESIII detector at the BEPCII collider, we report the observation of the decay J/ψ→ϕπ0, which is the first evidence for a doubly Okubo–Zweig–Iizuka suppressed electromagnetic J/ψ decay. A clear structure is observed in the K+K− mass spectrum around 1.02 GeV/c2, which can be attributed to interference between J/ψ→ϕπ0 and J/ψ→K+K−π0 decays. Due to this interference, two possible solutions are found. The corresponding measured values of the branching fraction of J/ψ→ϕπ0 are [2.94±0.16(stat)±0.16(syst)]×10−6 and [1.24±0.33(stat)±0.30(syst)]×10−7.

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.

Observation of a neutral structure near the DD¯* mass threshold in e+e− → (DD¯*)0π0 at √s = 4.226 and 4.257 GeV

Thu 06 Dec 2018 11:27:06 KRAT

A neutral structure in the DD¯∗ system around the DD¯∗ mass threshold is observed with a statistical significance greater than 10σ in the processes e+e−→D+D*−π0+c.c. and e+e−→D0D¯*0π0+c.c. at s√=4.226 and 4.257 GeV in the BESIII experiment. The structure is denoted as Zc(3885)0. Assuming the presence of a resonance, its pole mass and width are determined to be [3885.7+4.3−5.7(stat)±8.4(syst)] MeV/c2 and [35+11−12(stat)±15(syst)] MeV, respectively. The Born cross sections are measured to be σ[e+e−→Zc(3885)0π0,Zc(3885)0→DD¯∗]=[77±13(stat)±17(syst)] pb at 4.226 GeV and [47±9(stat)±10(syst)] pb at 4.257 GeV. The ratio of decay rates B[Zc(3885)0→D+D*−+c.c.]/B[Zc(3885)0→D0D¯*0+c.c.] is determined to be 0.96±0.18(stat)±0.12(syst), consistent with no isospin violation in the process, Zc(3885)0→DD¯∗.

Observation of the isospin-violating decay J /ψ →φπ0f0 (980)

Thu 06 Dec 2018 11:06:06 KRAT

Using a sample of 1.31×109 J/ψ events collected with the BESIII detector at the BEPCII collider, the decays J/ψ→ϕπ+π−π0 and J/ψ→ϕπ0π0π0 are investigated. The isospin-violating decay J/ψ→ϕπ0f0(980) with f0(980)→ππ is observed for the first time. The width of the f0(980) obtained from the dipion mass spectrum is found to be much smaller than the world average value. In the π0f0(980) mass spectrum, there is evidence of f1(1285) production. By studying the decay J/ψ→ϕη′, the branching fractions of η′→π+π−π0 and η′→π0π0π0, as well as their ratio, are also measured.

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 scalar diphoton resonances in the mass range 65–600 GeV with the ATLAS detector in pp collision data at √s = 8 TeV

Mon 17 Dec 2018 10:23:51 KRAT

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

Two-particle Bose–Einstein correlations in pp collisions at √s = 0.9 and 7 TeV measured with the ATLAS detector

Mon 10 Dec 2018 13:06:05 KRAT

The paper presents studies of Bose-Einstein Correlations (BEC) for pairs of like-sign charged particles measured in the kinematic range pT> 100 MeV and |η|< 2.5 in proton--proton collisions at centre-of-mass energies of 0.9 and 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. The integrated luminosities are approximately 7 μb−1, 190 μb−1 and 12.4 nb−1 for 0.9 TeV, 7 TeV minimum-bias and 7 TeV high-multiplicity data samples, respectively. The multiplicity dependence of the BEC parameters characterizing the correlation strength and the correlation source size are investigated for charged-particle multiplicities of up to 240. A saturation effect in the multiplicity dependence of the correlation source size is observed using the high-multiplicity 7 TeV data sample. The dependence of the BEC parameters on the average transverse momentum of the particle pair is also investigated.

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.

Study of dynamics of D0→K−e+νe and D0 → π−e+νe decays

Mon 10 Dec 2018 12:59:40 KRAT

In an analysis of a 2.92 fb−1 data sample taken at 3.773 GeV with the BESIII detector operated at the BEPCII collider, we measure the absolute decay branching fractions B(D0→K−e+νe)=(3.505±0.014±0.033)% and B(D0→π−e+νe)=(0.295±0.004±0.003)%. From a study of the differential decay rates we obtain the products of hadronic form factor and the magnitude of the Cabibbo-Kobayashi- Maskawa (CKM) matrix element fK+(0)|Vcs|=0.7172±0.0025±0.0035 and fπ+(0)|Vcd|=0.1435±0.0018±0.0009. Combining these products with the values of |Vcs(d)| from the SM constraint fit, we extract the hadronic form factors fK+(0)=0.7368±0.0026±0.0036 and fπ+(0)=0.6372±0.0080±0.0044, and their ratio fπ+(0)/fK+(0)=0.8649±0.0112±0.0073. These form factors and their ratio are used to test unquenched lattice QCD calculations of the form factors and a light cone sum rule (LCSR) calculation of their ratio. The measured value of fK(π)+(0)|Vcs(d)| and the lattice QCD value for fK(π)+(0) are used to extract values of the CKM matrix elements of |Vcs|=0.9601±0.0033±0.0047±0.0239 and |Vcd|=0.2155±0.0027±0.0014±0.0094, where the third errors are due to the uncertainties in lattice QCD calculations of the form factors. Using the LCSR value for fπ+(0)/fK+(0), we determine the ratio |Vcd|/|Vcs|=0.238±0.004±0.002±0.011, where the third error is from the uncertainty in the LCSR normalization. In addition, we measure form factor parameters for three different theoretical models that describe the weak hadronic charged currents for these two semileptonic decays. All of these measurements are the most precise to date.

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

Search for the isospin violating decay Υ(4260) → J/ψηπ0

Mon 10 Dec 2018 12:53:27 KRAT

Using data samples collected at center-of-mass energies of s√=4.009, 4.226, 4.257, 4.358, 4.416, and 4.599 GeV with the BESIII detector operating at the BEPCII storage ring, we search for the isospin violating decay Y(4260)→J/ψηπ0. No signal is observed, and upper limits on the cross section σ(e+e−→J/ψηπ0) at the 90% confidence level are determined to be 3.6, 1.7, 2.4, 1.4, 0.9, and 1.9 pb, respectively.

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 resonant diboson production in the ℓℓqq¯ final state in pp collisions at √s = 8 TeV with the ATLAS detector

Mon 10 Dec 2018 12:52:26 KRAT

This paper reports on a search for narrow resonances in diboson production in the q ¯q final state using pp collision data corresponding to an integrated luminosity of 20 fb−1 collected at √s = 8 TeV with the ATLAS detector at the Large Hadron Collider. No significant excess of data events over the StandardModel expectation is observed. Upper limits at the 95 % confidence level are set on the production cross section times branching ratio for Kaluza–Klein gravitons predicted by the Randall–Sundrum model and for Extended Gauge Model W bosons. These results lead to the exclusion of mass values below 740 and 1590 GeV for the graviton and W boson respectively.

Study of e+e- → ωχcJ at center of mass energies from 4.21 to 4.42 GeV

Mon 10 Dec 2018 12:52:24 KRAT

Based on data samples collected with the BESIII detector at the BEPCII collider at nine center of mass energies from 4.21 to 4.42 GeV, we search for the production of e+e−→ωχcJ (J=0, 1, 2). The process e+e−→ωχc0 is observed for the first time, and the Born cross sections at s√=4.23 and 4.26 GeV are measured to be (55.4±6.0±5.9) and (23.7±5.3±3.5) pb, respectively, where the first uncertainties are statistical and the second are systematic. The ωχc0 signals at the other seven energies and the e+e−→ωχc1 and ωχc2 signals are not significant, and the upper limits on the cross sections are determined. By examining the ωχc0 cross section as a function of center of mass energy, we find that it is inconsistent with the line shape of the Y(4260) observed in e+e−→π+π−J/ψ. Assuming the ωχc0 signals come from a single resonance, we extract the mass and width of the resonance to be (4230±8±6) MeV/c2 and (38±12±2) MeV, respectively, and the statistical significance is more than 9σ.

Searches for isospin-violating transitions χc0,2 → π0ηc

Mon 10 Dec 2018 12:52:21 KRAT

We present the first upper-limit measurement of the branching fractions of the isospin-violating transitions χc0,2→π0ηc. The measurements are performed using 106×106 ψ(3686) events accumulated with the BESIII detector at the BEPCII e+e− collider at a center-of-mass energy corresponding to the ψ(3686) mass. We obtained upper limits on the branching fractions at a 90% confidence level of B(χc0→π0ηc)<1.6×10−3 and B(χc2→π0ηc)<3.2×10−3.

Study of J/ψ → ηϕπ+π− at BESIII

Mon 10 Dec 2018 12:52:20 KRAT

Based on a sample of 2.25×108J/ψ events taken with the BESIII detector at the BEPCII collider, we present the results of a study of the decay J/ψ→ηϕπ+π−. The Y(2175) resonance is observed in the invariant mass spectrum of ϕf0(980) with a statistical significance of greater than 10σ. The corresponding mass and width are determined to be M=2200±6(stat)±5(syst) MeV/c2 and Γ=104±15(stat)±15(syst) MeV, respectively, and the product branching fraction is measured to be B(J/ψ→ηY(2175),Y(2175)→ϕf0(980),f0(980)→π+π−)=(1.20±0.14(stat)±0.37(syst))×10−4. The results are consistent within errors with those of previous experiments. We also measure the branching fraction of J/ψ→ϕf1(1285) with f1(1285)→ηπ+π− and set upper limits on the branching fractions for J/ψ→ϕη(1405)/ϕX(1835)/ϕX(1870) with η(1405)/X(1835)/X(1870)→ηπ+π− at the 90% confidence level.

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 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 Zc (3900))± → ωπ±

Mon 10 Dec 2018 12:17:49 KRAT

The decay Zc(3900)±→ωπ± is searched for using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies s√=4.23 and 4.26 GeV. No significant signal for the Zc(3900)± is found, and upper limits at the 90% confidence level on the Born cross section for the process e+e−→Zc(3900)±π∓→ωπ+π− are determined to be 0.26 and 0.18 pb at s√=4.23 and 4.26 GeV, respectively.

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 the Y(4140) via e+e- --> γϕJ/ψ at √s=4.23, 4.26 and 4.36 GeV

Mon 10 Dec 2018 12:17:09 KRAT

Using data samples collected at center-of-mass energies s√=4.23, 4.26, and 4.36 GeV with the BESIII detector operating at the BEPCII storage ring, we search for the production of the charmoniumlike state Y(4140) through a radiative transition followed by its decay to ϕJ/ψ. No significant signal is observed and upper limits on σ[e+e−→γY(4140)]⋅B(Y(4140)→ϕJ/ψ) at the 90% confidence level are estimated as 0.35, 0.28, and 0.33 pb at s√=4.23, 4.26, and 4.36 GeV, respectively.

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 D0 → γγ and improved measurement of the branching fraction for D0 → π0π0

Mon 10 Dec 2018 11:56:37 KRAT

Using 2.92 fb−1 of electron-positron annihilation data collected at s√=3.773 GeV with the BESIII detector, we report the results of a search for the flavor-changing neutral current process D0→γγ using a double-tag technique. We find no signal and set an upper limit at 90% confidence level for the branching fraction of B(D0→γγ)<3.8×10−6. We also investigate D0-meson decay into two neutral pions, obtaining a branching fraction of B(D0→π0π0)=(8.24±0.21(stat)±0.30(syst))×10−4, the most precise measurement to date and consistent with the current world average.

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 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

An improved limit for Γee of X(3872) and Γee measurement of ψ(3686)

Mon 03 Dec 2018 12:37:49 KRAT

Using the data sets taken at center-of-mass energies above 4 GeV by the BESIII detector at the BEPCII storage ring, we search for the reaction e+e- -> gamma_ISR X(3872) -> gamma_ISR pi+pi-J/psi via the Initial State Radiation technique. The production of a resonance with quantum numbers J^PC = 1^++ such as the X(3872) via single photon e+e- annihilation is forbidden, but is allowed by a next-to-leading order box diagram. We do not observe a significant signal of X(3872), and therefore give an upper limit for the electronic width times the branching fraction Gamma_ee^X(3872)Br(X(3872) -> pi+pi-Jpsi) < 0.13 eV at the 90% confidence level. This measurement improves upon existing limits by a factor of 46. Using the same final state, we also measure the electronic width of the psi(3686) to be Gamma_ee^psi(3686) = 2231 +- 18 +- 99 eV.

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.

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 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.

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 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 a CP-odd Higgs boson decaying to Zh in pp collisions at √s = 8 TeV with the ATLAS detector

Fri 07 Dec 2018 10:40:14 KRAT

A search for a heavy, CP-odd Higgs boson, A, decaying into a Zboson and a 125GeV Higgs boson, h, with the ATLAS detector at the LHC is presented. The search uses proton–proton collision data at a centre-of-mass energy of 8TeV corresponding to an integrated luminosity of 20.3fb−1. Decays of CP-even hbosons to ττor bbpairs with the Zboson decaying to electron or muon pairs are considered, as well as h →bbdecays with the Zboson decaying to neutrinos. No evidence for the production of an Aboson in these channels is found and the 95% confidence level upper limits derived for σ(gg→A) ×BR(A →Zh) ×BR(h →f¯f)are 0.098–0.013pb for f=τand 0.57–0.014pb for f=bin a range of mA=220–1000GeV. The results are combined and interpreted in the context of two-Higgs-doublet models.

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.

Precision measurement of the D*(0) decay branching fractions

Fri 07 Dec 2018 10:33:37 KRAT

Using 482 pb−1 of data taken at s√=4.009 GeV, we measure the branching fractions of the decays of D*0 into D0π0 and D0γ to be B(D*0→D0π0)=(65.5±0.8±0.5)% and B(D*0→D0γ)=(34.5±0.8±0.5)%, respectively, by assuming that the D*0 decays only into these two modes. The ratio of the two branching fractions is B(D*0→D0π0)/B(D*0→D0γ)=1.90±0.07±0.05, which is independent of the assumption made above. The first uncertainties are statistical and the second ones systematic. The precision is improved by a factor of 3 compared to the present world average values.

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.

Measurement of yCP in D0-D¯0 oscillation using quantum correlations in e+e- →D0D¯0 at √s = 3.773 GeV

Fri 07 Dec 2018 10:26:17 KRAT

We report a measurement of the parameter yCP in D0–D0 oscillations performed by taking advantage of quantum coherence between pairs of D0D0 mesons produced in e+e− annihilations near threshold. In this work, doubly-tagged D0D0 events, where one D decays to a CP eigenstate and the other D decays in a semileptonic mode, are reconstructed using a data sample of 2.92 fb−1 collected with the BESIII detector at the center-of-mass energy of √s = 3.773 GeV. We obtain yCP = (−2.0 ± 1.3 ± 0.7)%, where the first uncertainty is statistical and the second is systematic. This result is compatible with the current world average.

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 ψ(3686)→K−ΛΞ+ + c.c. and ψ(3686)→γK−ΛΞ+ + c.c.

Fri 07 Dec 2018 10:12:06 KRAT

Using a sample of 1.06×108ψ(3686) events produced in e+e− collisions at s√=3.686 GeV and collected with the BESIII detector at the BEPCII collider, we present studies of the decays ψ(3686)→K−ΛΞ¯++c.c. and ψ(3686)→γK−ΛΞ¯++c.c.. We observe two hyperons, Ξ(1690)− and Ξ(1820)−, in the K−Λ invariant mass distribution in the decay (3686)→K−ΛΞ¯++c.c. with significances of 4.9σ and 6.2σ, respectively. The branching fractions of (3686)→K−ΛΞ¯++c.c., ψ(3686)→K−Σ0Ξ¯++c.c., ψ(3686)→γχcJ→γK−ΛΞ¯++c.c. (J=0, 1, 2), and ψ(3686)→Ξ(1690/1820)−Ξ¯++c.c. with subsequent decay Ξ(1690/1820)−→K−Λ are measured for the first time.

Observation of a neutral charmoniumlike state Zc(4025)0 in e+e- → (DD¯)0π0

Fri 07 Dec 2018 09:51:05 KRAT

We report a study of the process e+e−→(D∗D¯∗)0π0 using e+e− collision data samples with integrated luminosities of 1092 pb−1 at s√=4.23 GeV and 826 pb−1 at s√=4.26 GeV collected with the BESIII detector at the BEPCII storage ring. We observe a new neutral structure near the (D∗D¯∗)0 mass threshold in the π0 recoil mass spectrum, which we denote as Zc(4025)0. Assuming a Breit-Wigner line shape, its pole mass and pole width are determined to be (4025.5+2.0−4.7±3.1) MeV/c2 and (23.0±6.0±1.0) MeV, respectively. The Born cross sections of e+e−→Zc(4025)0π0→(D∗D¯∗)0π0 are measured to be (61.6±8.2±9.0) pb at s√=4.23 GeV and (43.4±8.0±5.4) pb at s√=4.26 GeV. The first uncertainties are statistical and the second are systematic.