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DOE OSTI2018

Search for new phenomena in events with same-charge leptons and b -jets in p p collisions at s = 13 TeV with the ATLAS detector

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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurement of inclusive jet and dijet cross-sections in proton-proton collisions at s = 13 TeV with the ATLAS detector

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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Studies of Hadronic Physics with the BaBar Detector at SLAC and the Atlas Detector at the LHC

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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for lepton-flavour-violating decays of the Higgs and Z bosons with the ATLAS detector

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 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Search for electroweak production of charginos and sleptons decaying into final states with two leptons and missing transverse momentum in $$\sqrt{s}=13$$s=13 $$\text {TeV}$$TeV pp collisions using the ATLAS detector

© 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.

43 PARTICLE ACCELERATORS↗

DOE OSTI2019

Search for a right-handed gauge boson decaying into a high-momentum heavy neutrino and a charged lepton in p p collisions with the ATLAS detector at s = 13 TeV

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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Measurement of exclusive pion pair production in proton–proton collisions at $\sqrt{s}={7}\,\text {TeV}$ with the ATLAS detector

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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2013

Measurement of the inelastic proton-proton cross section with the ATLAS detector

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.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2016

Luminosity determination in pp collisions at $\sqrt{s} = 8$ TeV using the ATLAS detector at the LHC

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.

43 PARTICLE ACCELERATORS↗

DOE OSTI2015

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

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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

Search for Z* boson at ATLAS detector

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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Luminosity determination in $pp$ collisions at $\sqrt{s}=13$ TeV using the ATLAS detector at the LHC

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 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

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

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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

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

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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

A precise measurement of the jet energy scale derived from single-particle measurements and in situ techniques in proton–proton collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detector

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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Tools for estimating fake/non-prompt lepton backgrounds with the ATLAS detector at the LHC

Measurements and searches performed with the ATLAS detector at the CERN LHC often involve signatures with one or more prompt leptons. Such analyses are subject to 'fake/non-prompt' lepton backgrounds, where either a hadron or a lepton from a hadron decay or an electron from a photon conversion satisfies the prompt-lepton selection criteria. These backgrounds often arise within a hadronic jet because of particle decays in the showering process, particle misidentification or particle interactions with the detector material. As it is challenging to model these processes with high accuracy in simulation, their estimation typically uses data-driven methods. Three methods for carrying out this estimation are described, along with their implementation in ATLAS and their performance.

47 OTHER INSTRUMENTATION↗

DOE OSTI2018

Measurements of Cross Sections and Couplings of the Higgs Boson Using the ATLAS Detector

Measurements of cross sections and couplings of the Higgs boson using the ATLAS detector at CERN's LHC are presented. Data from proton proton collisions at $\sqrt{s}$ = 7, 8 and 13 TeV are discussed. A range of production and decay couplings can be tested with a precision that depends on the generality of the assumptions made. Data at 7 and 8 TeV are also combined with CMS results to enhance the precision. The results are all consistent with predictions of the Standard Model..

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

Search for W ′ → t b → q q b b decays in p p collisions at s = 8 TeV with the ATLAS detector

A search for a massive WPRIME gauge boson is performed with the ATLAS detector at the LHC in P P collisions at a centre-of-mass energy of sqrt(s) = 8 TeV, corresponding to 20.3 fb-1 of integrated luminosity. This analysis is done in the WPRIME --> TOP BOTTOM --> QUARK QUARK BOTTOM BOTTOM mode for WPRIME masses above 1.5 TeV, where the WPRIME decay products are highly boosted. Novel jet substructure techniques are used to identify jets from high-momentum top quarks to ensure high sensitivity, independent of WPRIME mass, up to 3 TeV; b-tagging is also used to identify jets originating from b-quarks. The data are consistent with Standard Model background-only expectations, and upper limits at 95% confidence level are set on the WPRIME --> TOP BOTTOM cross section times branching ratio ranging from 0.16 pb to 0.33 pb for left-handed WPRIME bosons, and ranging from 0.10 pb to 0.21 pb for WPRIME bosons with purely right-handed couplings. Upper limits at 95% confidence level are set on the WPRIME-boson coupling to TOP BOTTOM as a function of the WPRIME mass using an effective field theory approach, which is independent of details of particular models predicting a WPRIME boson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗