High- E T isolated-photon plus jets production in pp collisions at s = 8 TeV with the ATLAS detector
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Engineering topics
Adomeit, S.
Publications and source records attributed to Adomeit, S..
Measurement of the W boson polarisation in $t\bar{t}$ events from pp collisions at $\sqrt{s} = 8$ TeV in the lepton + jets channel with ATLAS
This paper presents a measurement of the polarisation of $W$ bosons from $t\bar{t}$ decays, reconstructed in events with one high-$p_{\mbox{T}}$ lepton and at least four jets. Data from $pp$ collisions at the LHC were collected at $\sqrt{s}$ = 8 TeV and correspond to an integrated luminosity of 20.2 fb$^{-1}$. The angle $\theta^{*}$ between the $b$-quark from the top quark decay and a direct $W$ boson decay product in the $W$ boson rest frame is sensitive to the $W$ boson polarisation. Two different $W$ decay products are used as polarisation analysers: the charged lepton and the down-type quark for the leptonically and hadronically decaying $W$ boson, respectively. The most precise measurement of the $W$ boson polarisation via the distribution of $\cos{\theta^{*}}$ is obtained using the leptonic analyser and events in which at least two of the jets are tagged as $b$-quark jets. The fitted fractions of longitudinal, left- and right-handed polarisation states are $F_{\mathrm{0}}= 0.709 \pm {0.019}$, $F_{\mathrm{L}}= 0.299 \pm {0.015}$ and $F_{\mathrm{R}}= -0.008 \pm {0.014}$, and are the most precisely measured $W$ boson polarisation fractions to date. Limits on anomalous couplings of the $Wtb$ vertex are set.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Probing the W tb vertex structure in t -channel single-top-quark production and decay in pp collisions at $ \sqrt{s}=8 $ TeV with the ATLAS detector
To probe the W tb vertex structure, top-quark and W -boson polarisation observables are measured from t-channel single-top-quark events produced in proton-proton collisions at a centre-of-mass energy of 8 TeV. The dataset corresponds to an integrated luminosity of 20.2 fb –1 , recorded with the ATLAS detector at the LHC. Selected events contain one isolated electron or muon, large missing transverse momentum and exactly two jets, with one of them identified as likely to contain a b -hadron. Stringent selection requirements are applied to discriminate t -channel single-top-quark events from background. The polarisation observables are extracted from asymmetries in angular distributions measured with respect to spin quantisation axes appropriately chosen for the top quark and the W boson. The asymmetry measurements are performed at parton level by correcting the observed angular distributions for detector effects and hadronisation after subtracting the background contributions. Here, the measured top-quark and W -boson polarisation values are in agreement with the Standard Model predictions. Limits on the imaginary part of the anomalous coupling g R are also set from model-independent measurements.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the inclusive cross-sections of single top-quark and top-antiquark t-channel production in pp collisions at $ \sqrt{s}=13 $ TeV with the ATLAS detector
A measurement of the t-channel single-top-quark and single-top-antiquark production cross-sections in the lepton+jets channel is presented, using 3.2 fb –1 of proton-proton collision data at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC in 2015. Events are selected by requiring one charged lepton (electron or muon), missing transverse momentum, and two jets with high transverse momentum, exactly one of which is required to be b-tagged. Using a binned maximum-likelihood fit to the discriminant distribution of a neural network, the cross-sections are determined to be σ(tq) = 156 ± 5 (stat.) ± 27 (syst.) ± 3 (lumi.) pb for single top-quark production and σ(t¯q)=91±4 (stat.) ± 18 (syst.) ± 2 (lumi.) pb for single top-antiquark production, assuming a top-quark mass of 172.5 GeV. The cross-section ratio is measured to be R t = σ(tq)/σ(t¯q)=1.72±0.09 (stat.) ± 0.18 (syst.). All results are in agreement with Standard Model predictions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Performance of algorithms that reconstruct missing transverse momentum in $\sqrt{s}=8$ TeV proton–proton collisions in the ATLAS detector
The reconstruction and calibration algorithms used to calculate missing transverse momentum (E miss T ) with the ATLAS detector exploit energy deposits in the calorimeter and tracks reconstructed in the inner detector as well as the muon spectrometer. Various strategies are used to suppress effects arising from additional proton–proton interactions, called pileup, concurrent with the hard-scatter processes. Tracking information is used to distinguish contributions from the pileup interactions using their vertex separation along the beam axis. The performance of the E miss T reconstruction algorithms, especially with respect to the amount of pileup, is evaluated using data collected in proton–proton collisions at a centre-of-mass energy of 8 TeV during 2012, and results are shown for a data sample corresponding to an integrated luminosity of 20.3fb –1 . The simulation and modelling of E miss T in events containing a Z boson decaying to two charged leptons (electrons or muons) or a W boson decaying to a charged lepton and a neutrino are compared to data. The acceptance for different event topologies, with and without high transverse momentum neutrinos, is shown for a range of threshold criteria for E miss T , and estimates of the systematic uncertainties in the E miss T measurements are presented.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the t t ¯ production cross section in the τ + jets final state in p p collisions at s = 8 TeV using the ATLAS detector
A measurement of the inclusive p p → t $\bar{t}$ + X production cross section in the τ + jets final state using only the hadronic decays of the τ lepton is presented. The measurement is performed using 20.2 fb -1 of proton-proton collision data recorded at a center-of-mass energy of √ s = 8 TeV with the ATLAS detector at the Large Hadron Collider. The cross section is measured via a counting experiment by imposing a set of selection criteria on the identification and kinematic variables of the reconstructed particles and jets, and on event kinematic variables and characteristics. The production cross section is measured to be σ t $\bar{t}$ = 239 ± 29 pb , which is in agreement with the measurements in other final states and the theoretical predictions at this center-of-mass energy.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of jet activity produced in top-quark events with an electron, a muon and two b -tagged jets in the final state in pp collisions at √s = 13 TeV with the ATLAS detector
Measurements of jet activity in top-quark pair events produced in proton–proton collisions are presented, using 3.2 fb –1 of pp collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS experiment at the Large Hadron Collider. Events are chosen by requiring an opposite-charge eμ pair and two b-tagged jets in the final state. The normalised differential cross-sections of top-quark pair production are presented as functions of additional-jet multiplicity and transverse momentum, p T . The fraction of signal events that do not contain additional jet activity in a given rapidity region, the gap fraction, is measured as a function of the p T threshold for additional jets, and is also presented for different invariant mass regions of the eμbb¯ system. All measurements are corrected for detector effects and presented as particle-level distributions compared to predictions with different theoretical approaches for QCD radiation. While the kinematics of the jets from top-quark decays are described well, the generators show differing levels of agreement with the measurements of observables that depend on the production of additional jets.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Electron efficiency measurements with the ATLAS detector using 2012 LHC proton–proton collision data
This paper describes the algorithms for the reconstruction and identification of electrons in the central region of the ATLAS detector at the Large Hadron Collider (LHC). These algorithms were used for all ATLAS results with electrons in the final state that are based on the 2012 pp collision data produced by the LHC at s = 8 TeV. The efficiency of these algorithms, together with the charge misidentification rate, is measured in data and evaluated in simulated samples using electrons from Z→ ee, Z→ eeγ and J/ ψ→ ee decays. For these efficiency measurements, the full recorded data set, corresponding to an integrated luminosity of 20.3 fb - 1 , is used. Based on a new reconstruction algorithm used in 2012, the electron reconstruction efficiency is 97% for electrons with E T = 15 GeV and 99% at E T = 50 GeV. Combining this with the efficiency of additional selection criteria to reject electrons from background processes or misidentified hadrons, the efficiency to reconstruct and identify electrons at the ATLAS experiment varies from 65 to 95%, depending on the transverse momentum of the electron and background rejection.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurements of top quark spin observables in $ t\overline{t} $ events using dilepton final states in $ \sqrt{s}=8 $ TeV pp collisions with the ATLAS detector
Measurements of top quark spin observables in tt¯ events are presented based on 20.2 fb –1 of √s = 8 TeV proton-proton collisions recorded with the ATLAS detector at the LHC. The analysis is performed in the dilepton final state, characterised by the presence of two isolated leptons (electrons or muons). There are 15 observables, each sensitive to a different coefficient of the spin density matrix of tt¯ production, which are measured independently. Ten of these observables are measured for the first time. All of them are corrected for detector resolution and acceptance effects back to the parton and stable-particle levels. The measured values of the observables at parton level are compared to Standard Model predictions at next-to-leading order in QCD. The corrected distributions at stable-particle level are presented and the means of the distributions are compared to Monte Carlo predictions. No significant deviation from the Standard Model is observed for any observable.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for triboson $W^{\pm }W^{\pm }W^{\mp }$ production in $pp$ collisions at $\sqrt{s}=8$ $\text {TeV}$ with the ATLAS detector
This paper reports a search for triboson W ± W ± W ∓ production in two decay channels (W ± W ± W ∓ → ℓ ± νℓ ± νℓ ∓ ν and W ± W ± W ∓ → ℓ ± νℓ ± νjj with ℓ = e,μ) in proton-proton collision data corresponding to an integrated luminosity of 20.3 fb –1 at a centre-of-mass energy of 8 TeV with the ATLAS detector at the Large Hadron Collider. Events with exactly three charged leptons, or two leptons with the same electric charge in association with two jets, are selected. The total number of events observed in data is consistent with the Standard Model (SM) predictions. The observed 95% confidence level upper limit on the SM W ± W ± W ∓ production cross section is found to be 730 fb with an expected limit of 560 fb in the absence of SM W ± W ± W ∓ production. Limits are also set on WWWW anomalous quartic gauge couplings.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for anomalous electroweak production of W W / W Z in association with a high-mass dijet system in p p collisions at s = 8 TeV with the ATLAS detector
A search is presented for anomalous quartic gauge boson couplings in vector-boson scattering. Here, the data for the analysis correspond to 20.2 fb -1 of √ s = 8 TeV pp collisions and were collected in 2012 by the ATLAS experiment at the Large Hadron Collider. The search looks for the production of WW or WZ boson pairs accompanied by a high-mass dijet system, with one W decaying leptonically and a W or Z decaying hadronically. The hadronically decaying W/Z is reconstructed as either two small-radius jets or one large-radius jet using jet substructure techniques. Constraints on the anomalous quartic gauge boson coupling parameters α 4 and α 5 are set by fitting the transverse mass of the diboson system, and the resulting 95% confidence intervals are - 0.024 < α 4 < 0.030 and - 0.028 < α 5 < 0.033 .
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurements of charge and CP asymmetries in b -hadron decays using top-quark events collected by the ATLAS detector in pp collisions at $ \sqrt{s}=8 $ TeV
Same- and opposite-sign charge asymmetries are measured in lepton+jets tt¯ events in which a b-hadron decays semileptonically to a soft muon, using data corresponding to an integrated luminosity of 20.3 fb –1 from proton-proton collisions at a centre-of-mass energy of √s = 8 TeV collected with the ATLAS detector at the Large Hadron Collider at CERN. The charge asymmetries are based on the charge of the lepton from the top-quark decay and the charge of the soft muon from the semileptonic decay of a b-hadron and are measured in a fiducial region corresponding to the experimental acceptance. Four CP asymmetries (one mixing and three direct) are measured and are found to be compatible with zero and consistent with the Standard Model.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the prompt J /$\psi$ pair production cross-section in pp collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector
The production of two prompt J/ψ mesons, each with transverse momenta p T > 8.5 GeV and rapidity |y| < 2.1, is studied using a sample of proton-proton collisions at $\sqrt{s} = 8$ TeV, corresponding to an integrated luminosity of 11.4 fb –1 collected in 2012 with the ATLAS detector at the LHC. The differential cross-section, assuming unpolarised J/ψ production, is measured as a function of the transverse momentum of the lower-p T J/ψ meson, di-J/ψp T and mass, the difference in rapidity between the two J/ψ mesons, and the azimuthal angle between the two J/ψ mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two J/ψ mesons. The total and double parton scattering cross-sections are compared with predictions. The effective cross-section of double parton scattering is measured to be σ eff = 6.3 ± 1.6(stat)±1.0(syst) mb.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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↗
Search for dark matter in association with a Higgs boson decaying to b-quarks in pp collisions at s = 13 TeV with the ATLAS detector
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for new resonances decaying to a W or Z boson and a Higgs boson in the ℓ + ℓ − b b ¯ , ℓ ν b b ¯ , and ν ν ¯ b b ¯ channels with pp collisions at s = 13 TeV with the ATLAS detector
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of W boson angular distributions in events with high transverse momentum jets at s = 8 TeV using the ATLAS detector
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurements of ψ(2S) and X(3872) → J/ψπ + π - production in pp collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector
Differential cross sections are presented for the prompt and non-prompt production of the hidden-charm states X(3872) and ψ(2S), in the decay mode J/ψπ + π – , measured using 11.4 fb –1 of pp collisions at √s = 8 TeV by the ATLAS detector at the LHC. The ratio of cross-sections X(3872)/ψ(2S) is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of X(3872) and ψ(2S). Assuming independent single effective lifetimes for non-prompt X(3872) and ψ(2S) production gives R B = B(B→X(3872)+any)B(X(3872)→J/ψπ+π–)/B(B→ψ(2S)+any)B(ψ(2S)→J/ψπ+π–)=(3.95±0.32(stat)±0.08(sys))×10 –2 separating short- and long-lived contributions, assuming that the short-lived component is due to B c decays, gives R B = (3.57 ± 0.33(stat) ± 0.11(sys)) × 10 –2 , with the fraction of non-prompt X(3872) produced via B c decays for p T (X(3872)) > 10 GeV being (25 ± 13(stat) ± 2(sys) ± 5(spin))%. The distributions of the dipion invariant mass in the X(3872) and ψ(2S) decays are also measured and compared to theoretical predictions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗