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CERN-LHC, ATLAS HEP data for the Search for resonant W Z Production in the fully leptonic final state in Proton-Proton Collisions at sqrt(s) = 13 TeV with the ATLAS Detector.
CERN-LHC, ATLAS. Limits on pair production of a heavy vector-like B quark together with its antiparticle, where the B quark decays to a W boson and a top quark. The search is based on 36.1 +\- 0.8 fb^{-1} of pp collisions at sqrt{s} = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton plus jets final state, including at least four small jets out of which at least one is required to be b-tagged jet and a large-radius jet. Mass limits on B production are set as a function of the decay branching ratios.
CERN-LHC, ATLAS. This result is a search for new phenomena in events with two same-charge leptons or three leptons and jets identified as originating from b-quarks in a data sample of 36.1 fb−1 of pp collisions at √s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. No significant excess is found and limits are set on vector-like quark, four-top-quark, and same-sign top-quark pair production.
Measurement of inclusive jet cross-sections with the ATLAS Detector at a centre-of-mass energy 13 TeV Inclusive jet and dijet cross-sections are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurement uses a dataset with an integrated luminosity of 3.2 fb$^{−1} recorded in 2015 with the ATLAS detector at the Large Hadron Collider. Jets are identified using the anti-kt algorithm with a radius parameter value of R=0.4. The inclusive jet cross-sections are measured double-differentially as a function of the jet transverse momentum, covering the range from 100 GeV to 3.5 TeV, and the absolute jet rapidity up to |y|=3. The double-differential dijet production cross-sections are presented as a function of the dijet mass, covering the range from 300 GeV to 9 TeV, and the half absolute rapidity separation between the two leading jets within |y|<3, y∗, up to y∗=3. Next-to-leading-order, and next-to-next-to-leading-order for the inclusive jet measurement, perturbative QCD calculations corrected for non-perturbative and electroweak effects are compared to the measured cross-sections.
The University of Louisville High Energy Physics group contributed significantly to the success of the BaBar Experiment at SLAC and the Mu2e Experiment at Fermilab. In particular, they have contributed to understanding hadronic processes in electron-positron annihilation and charged lepton flavor violation in a very rare muon conversion process. Both are high-precision undertakings at the Intensity Frontier of High Energy Physics.
Direct searches for lepton flavour violation in decays of the Higgs and Z bosons with the ATLAS detector at the LHC are presented. The following three decays are considered: H → eτ, H → μτ, and Z → μτ. The searches are based on the data sample of proton–proton collisions collected by the ATLAS detector corresponding to an integrated luminosity of 20.3 fb –1 at a centre-of-mass energy of √s = 8 TeV. No significant excess is observed, and upper limits on the lepton-flavour-violating branching ratios are set at the 95% confidence level: Br(H → eτ) < 1.04%, Br(H → μτ) < 1.43%, and Br(Z → μτ) < 1.69 × 10 –5 .
© 2020, CERN for the benefit of the ATLAS collaboration. A search for the electroweak production of charginos and sleptons decaying into final states with two electrons or muons is presented. The analysis is based on 139 fb- 1 of proton–proton collisions recorded by the ATLAS detector at the Large Hadron Collider at s=13 TeV. Three R-parity-conserving scenarios where the lightest neutralino is the lightest supersymmetric particle are considered: the production of chargino pairs with decays via either W bosons or sleptons, and the direct production of slepton pairs. The analysis is optimised for the first of these scenarios, but the results are also interpreted in the others. No significant deviations from the Standard Model expectations are observed and limits at 95% confidence level are set on the masses of relevant supersymmetric particles in each of the scenarios. For a massless lightest neutralino, masses up to 420 Ge are excluded for the production of the lightest-chargino pairs assuming W-boson-mediated decays and up to 1 TeV for slepton-mediated decays, whereas for slepton-pair production masses up to 700 Ge are excluded assuming three generations of mass-degenerate sleptons.
CERN-LHC, ATLAS. A search for a right-handed gauge boson WR, decaying into a boosted right-handed heavy neutrino NR, in the framework of Left-Right Symmetric Models is presented. It is based on data from proton-proton collisions with a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015, 2016 and 2017, corresponding to an integrated luminosity of 80 fb−1. The search is performed separately for electrons and muons in the final state. A distinguishing feature of the search is the use of large-radius jets containing electrons. Selections based on the signal topology result in smaller background compared with to expected signal. No significant deviation from the Standard Model prediction is observed and lower limits are set in the WR and NR mass plane. Mass values of the WR smaller than 3.8-5 TeV are excluded for NR in the mass range 0.1-1.8 TeV.
The exclusive production of pion pairs in the process $pp$ → $pp π$ + $π$ - has been measured at $\sqrt{s}={7}\,\text {TeV}$ with the ATLAS detector at the LHC, using $80 µb$ -1 of low-luminosity data. The pion pairs were detected in the ATLAS central detector while outgoing protons were measured in the forward ATLAS ALFA detector system. This rep resents the first use of proton tagging to measure an exclusive hadronic final state at the LHC. A cross-section measurement is performed in two kinematic regions defined by the pro ton momenta, the pion rapidities and transverse momenta, and the pion–pion invariant mass. Cross-section values of $4.8 ± 1.0$ ${(stat)}^{+0.3}_{-0.2}$ $(syst) µ b$ and $9 ± 6$ ${(stat)}^{+2}_{-2}$ $(syst) µ b$ are obtained in the two regions; they are compared with theoretical models and provide a demonstration of the feasibility of measurements of this type.
A measurement of the inelastic proton-proton cross-section at centre-of-mass energy of Central diffraction in proton-proton collisions at {radical}(s) = 7TeV using the ATLAS detector at the Large Hadron Collider is presented. Events are selected by requiring hits in scintillator counters mounted in the forward region of the ATLAS detector and the dataset corresponding to an integrated luminosity of 20{mu}b{sup -1}. In addition, the total cross-section is studied as a function of the rapidity gap size measured with the inner detector and calorimetry.
The luminosity determination for the ATLAS detector at the LHC during pp collisions at $\sqrt{s} = 8$ TeV in 2012 is presented. The evaluation of the luminosity scale is performed using several luminometers, and comparisons between these luminosity detectors are made to assess the accuracy, consistency and long-term stability of the results. A luminosity uncertainty of $δL/L$= ± 1.9% is obtained for the 22.7fb –1 of pp collision data delivered to ATLAS at $\sqrt{s} = 8$ TeV in 2012.
Double-differential three-jet production cross-sections are measured in proton–proton collisions at a centre-of-mass energy of √s=7TeV using the ATLAS detector at the large hadron collider. The measurements are presented as a function of the three-jet mass (m jjj ), 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 11 . Jets are identified using the anti-k t 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.
New metastable massive particles with electric and color charge are features of many theories beyond the Standard Model. A search is performed for long-lived gluino-based R-hadrons with the ATLAS detector at the LHC using a data sample corresponding to an integrated luminosity of 31 pb{sup -1}. We search for evidence of particles that have come to rest in the ATLAS detector and decay at some later time during the periods in the LHC bunch structure without proton-proton collisions. No significant deviations from the expected backgrounds are observed, and a cross-section limit is set. It can be interpreted as excluding gluino-based R-hadrons with masses less than 341 GeV at the 95 % C.L., for lifetimes from 10{sup -5} to 10{sup 3} seconds and a neutralino mass of 100 GeV.
We present the results of the search for new excited Z* boson at ATLAS detector in 2011. Results: are based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.9 fb{sup −1} in the dielectron channel and 5.0 fb{sup −1} in the dimuon channel. Since good agreement between experimental data and expectation of the Standard Model is observed in both channels, the existence of Z* is excluded with 95 percent confidence level for all masses below 2.20 TeV. The plans for Z* search in 2012 are discussed.
The luminosity determination for the ATLAS detector at the LHC during Run 2 is presented, with pp collisions at a centre-of-mass energy $\sqrt{s}$ = 13 TeV. The absolute luminosity scale is determined using van der Meer beam separation scans during dedicated running periods in each year, and extrapolated to the physics data-taking regime using complementary measurements from several luminosity-sensitive detectors. The total uncertainties in the integrated luminosity for each individual year of data taking range from 0.9% to 1.1%, and are partially corre lated between years. After standard data-quality selections, the full Run 2 pp data sample corresponds to an integrated luminosity of 140.1 ± 1.2 fb -1 , i.e. an uncertainty of 0.83%. A dedicated sample of low-pileup data recorded in 2017– 2018 for precision Standard Model physics measurements is analysed separately, and has an integrated luminosity of 338.1 ± 3.1 pb -1 .
CERN-LHC. Double-differential three-jet cross-sections have been measured in proton-proton collisions at a centre-of-mass energy of sqrt(s)=7 TeV using the ATLAS detector at the Large Hadron Collider. The measurements are presented as functions of the three-jet invariant mass (m_jjj) and the sum of 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 the sample of proton-proton collision 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 this measurement 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.
CERN-LHC. This article reports on a search for dark matter pair production in association with bottom or top quarks in 20.3 fb 8 of pp collisions collected at sqrt(s) = 8 TeV by the ATLAS detector at the LHC. Events with large missing 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=8 TeV by the ATLAS detector at the LHC. Events with large missing 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.
The jet energy calibration and its uncertainties are derived from measurements of the calorimeter response to single particles in both data and Monte Carlo simulation using proton–proton collisions at $\sqrt{s} = 13$ TeV collected with the ATLAS detector during Run 2 at the Large Hadron Collider. The jet calibration uncertainty for anti-$k_T$ jets with a jet radius parameter of R$_\textrm{jet} = 0.4$ and in the central jet rapidity region is about 2.5% for transverse momenta ($p_{\text {T}}$) of 20 $\text {GeV}$ , about 0.5% for $p_{\text {T}} = 300$ GeV and 0.7% for $p_{\text {T}} = 4$ TeV . Excellent agreement is found with earlier determinations obtained from -balance based in situ methods ($Z/\gamma$ +jets). The combination of these two independent methods results in the most precise jet energy measurement achieved so far with the ATLAS detector with a relative uncertainty of 0.3% at $p_\textrm{T} = 300$ GeV and 0.6% at 4 TeV. The jet energy calibration is also derived with the single-particle calorimeter response measurements separately for quark- and gluon-induced jets and furthermore for jets with R jet varying from 0.2 to 1.0 retaining the correlations between these measurements. Differences between inclusive jets and jets from boosted top-quark decays, with and without grooming the soft jet constituents, are also studied.