Search for heavy charged long-lived particles in the ATLAS detector in 31.6 fb$^{-1}$ of proton-proton collision data at $\sqrt{s} = 13$ TeV

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
No Journal Information, 2019.
Inspire Record 1718558 DOI 10.17182/hepdata.86565

A search for heavy charged long-lived particles is performed using a data sample of 31.6 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 13$ TeV collected by the ATLAS experiment at the Large Hadron Collider. The search is based on observables related to ionization energy loss and time of flight, which are sensitive to the velocity of heavy charged particles traveling significantly slower than the speed of light. Multiple search strategies for a wide range of lifetimes, corresponding to path lengths of a few meters, are defined as model-independently as possible, by referencing several representative physics cases that yield long-lived particles within supersymmetric models, such as gluinos/squarks ($R$-hadrons), charginos and staus. No significant deviations from the expected Standard Model background are observed. Upper limits at 95% confidence level are provided on the production cross sections of long-lived $R$-hadrons as well as directly pair-produced staus and charginos. These results translate into lower limits on the masses of long-lived gluino, sbottom and stop $R$-hadrons, as well as staus and charginos of 2000 GeV, 1250 GeV, 1340 GeV, 430 GeV and 1090 GeV, respectively.

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Lower mass requirement for signal regions.

Lower mass requirement for signal regions.

Expected and observed events in the 16 discovery regions along with the according control regions.

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Search for low-mass resonances decaying into two jets and produced in association with a photon using $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
No Journal Information, 2019.
Inspire Record 1717700 DOI 10.17182/hepdata.85763

A search is performed for localised excesses in dijet mass distributions of low-dijet-mass events produced in association with a high transverse energy photon. The search uses up to 79.8 fb$^{-1}$ of LHC proton-proton collisions collected by the ATLAS experiment at a centre-of-mass energy of 13 TeV during 2015-2017. Two variants are presented: one which makes no jet flavour requirements and one which requires both jets to be tagged as $b$-jets. The observed mass distributions are consistent with multi-jet processes in the Standard Model. The data are used to set upper limits on the production cross-section for a benchmark $Z^\prime$ model and, separately, on generic Gaussian-shape contributions to the mass distributions, extending the current ATLAS constraints on dijet resonances to the mass range between 225 and 1100 GeV.

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Dijet mass distribution for the flavour inclusive category. Data, estimated background and uncertainties are shown. Events are collected using the single-photon trigger and contain a $E_T^{\gamma} > 150$ GeV photon and two $p_T^{jet} > 25$ GeV jets.

Dijet mass distribution for the flavour inclusive category. Data, estimated background and uncertainties are shown. Events are collected using the combined trigger and contain a $E_T^{\gamma} > 95$ GeV photon and two $p_T^{jet} > 65$ GeV jets.

Dijet mass distribution for the b-tagged category. Data, estimated background and uncertainties are shown. Events are collected using the single-photon trigger and contain a $E_T^{\gamma} > 150$ GeV photon and two $p_T^{jet} > 25$ GeV jets.

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Measurement of the inclusive and fiducial $t\bar{t}$ production cross-sections in the lepton+jets channel in $pp$ collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Eur.Phys.J. C78 (2018) 487, 2018.
Inspire Record 1644099 DOI 10.17182/hepdata.81945

The inclusive and fiducial $t\bar{t}$ production cross-sections are measured in the lepton+jets channel using $20.2~\hbox {fb}^{-1}$ of proton–proton collision data at a centre-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. Major systematic uncertainties due to the modelling of the jet energy scale and b-tagging efficiency are constrained by separating selected events into three disjoint regions. In order to reduce systematic uncertainties in the most important background, the $W \text {+\,jets}$ process is modelled using $Z$ + jets events in a data-driven approach. The inclusive $t\bar{t}$ cross-section is measured with a precision of 5.7% to be $\sigma _{\text {inc}}(t\bar{t}) = 248.3 \pm 0.7 \, ({\mathrm {stat.}}) \pm 13.4 \, ({\mathrm {syst.}}) \pm 4.7 \, ({\mathrm {lumi.}})~\text {pb}$ , assuming a top-quark mass of 172.5 GeV. The result is in agreement with the Standard Model prediction. The cross-section is also measured in a phase space close to that of the selected data. The fiducial cross-section is $\sigma _{\text {fid}}(t\bar{t}) = 48.8 \pm 0.1 \, ({\mathrm {stat.}}) \pm 2.0 \, ({\mathrm {syst.}}) \pm 0.9 \, ({\mathrm {lumi.}})~\text {pb}$ with a precision of 4.5%.

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Measurement of the $ t\overline{t}\gamma $ production cross section in proton-proton collisions at $ \sqrt{s}=8 $ TeV with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
JHEP 1711 (2017) 086, 2017.
Inspire Record 1604029 DOI 10.17182/hepdata.81946

The cross section of a top-quark pair produced in association with a photon is measured in proton-proton collisions at a centre-of-mass energy of $ \sqrt{s}=8 $ TeV with 20.2 fb$^{−1}$ of data collected by the ATLAS detector at the Large Hadron Collider in 2012. The measurement is performed by selecting events that contain a photon with transverse momentum p$_{T}$ > 15 GeV, an isolated lepton with large transverse momentum, large missing transverse momentum, and at least four jets, where at least one is identified as originating from a b-quark. The production cross section is measured in a fiducial region close to the selection requirements. It is found to be 139 ± 7 (stat.) ± 17 (syst.) fb, in good agreement with the theoretical prediction at next-to-leading order of 151 ± 24 fb. In addition, differential cross sections in the fiducial region are measured as a function of the transverse momentum and pseudorapidity of the photon.

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The measured fiducial cross sections. The first uncertainty is the statistical uncertainty and the second is the systematic uncertainty

differential cross section as function of the photon pT. The first uncertainty is the statistical uncertainty and the second is the systematic uncertainty

differential cross section as function of the photon pseudorapidity. The first uncertainty is the statistical uncertainty and the second is the systematic uncertainty


Measurement of forward-backward multiplicity correlations in lead-lead, proton-lead, and proton-proton collisions with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Phys.Rev. C95 (2017) 064914, 2017.
Inspire Record 1472317 DOI 10.17182/hepdata.87144

Two-particle pseudorapidity correlations are measured in sNN=2.76TeVPb+Pb, sNN=5.02TeVp+Pb, and s=13TeVpp collisions at the Large Hadron Collider (LHC), with total integrated luminosities of approximately 7μb−1, 28 nb−1, and 65 nb−1, respectively. The correlation function CN(η1,η2) is measured as a function of event multiplicity using charged particles in the pseudorapidity range |η|<2.4. The correlation function contains a significant short-range component, which is estimated and subtracted. After removal of the short-range component, the shape of the correlation function is described approximately by 1+〈a12〉1/2η1η2 in all collision systems over the full multiplicity range. The values of 〈a12〉1/2 are consistent for the opposite-charge pairs and same-charge pairs, and for the three collision systems at similar multiplicity. The values of 〈a12〉1/2 and the magnitude of the short-range component both follow a power-law dependence on the event multiplicity. The short-range component in p + Pb collisions, after symmetrizing the proton and lead directions, is found to be smaller at a given η than in pp collisions with comparable multiplicity.

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a1 from fit C_N^sub(eta-) for p+Pb, pT>0.5GeV

a1 from fit C_N^sub(eta-) for p+Pb, pT>0.2GeV

a1 from fit C_N^sub(eta+) for p+Pb, pT>0.5GeV

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Measurements of fiducial and differential cross-sections of $t\bar{t}$ production with additional heavy-flavour jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
No Journal Information, 2018.
Inspire Record 1705857 DOI 10.17182/hepdata.87098

This paper presents measurements of $t\bar{t}$ production in association with additional $b$-jets in $pp$ collisions at the LHC at a centre-of-mass energy of 13 TeV. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb$^{-1}$. Fiducial cross-section measurements are performed in the dilepton and lepton-plus-jets $t\bar{t}$ decay channels. Results are presented at particle level in the form of inclusive cross-sections of $t\bar{t}$ final states with three and four $b$-jets as well as differential cross-sections as a function of global event properties and properties of $b$-jet pairs. The measured inclusive fiducial cross-sections generally exceed the $t\bar{t}b\bar{b}$ predictions from various next-to-leading-order matrix element calculations matched to a parton shower but are compatible within the total uncertainties. The experimental uncertainties are smaller than the uncertainties in the predictions. Comparisons of state-of-the-art theoretical predictions with the differential measurements are shown and good agreement with data is found for most of them.

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Measurement of photon–jet transverse momentum correlations in 5.02 TeV Pb + Pb and $pp$ collisions with ATLAS

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Phys.Lett. B789 (2019) 167-190, 2019.
Inspire Record 1694678 DOI 10.17182/hepdata.85369

Jets created in association with a photon can be used as a calibrated probe to study energy loss in the medium created in nuclear collisions. Measurements of the transverse momentum balance between isolated photons and inclusive jets are presented using integrated luminosities of 0.49 nb$^{-1}$ of Pb+Pb collision data at $\sqrt{s_\mathrm{NN}}=5.02$ TeV and 25 pb$^{-1}$ of $pp$ collision data at $\sqrt{s}=5.02$ TeV recorded with the ATLAS detector at the LHC. Photons with transverse momentum $63.1 < p_\mathrm{T}^{\gamma} < 200$ GeV and $\left|\eta^{\gamma}\right| < 2.37$ are paired inclusively with all jets in the event that have $p_\mathrm{T}^\mathrm{jet} > 31.6$ GeV and pseudorapidity $\left|\eta^\mathrm{jet}\right| < 2.8$. The transverse momentum balance given by the jet-to-photon $p_\mathrm{T}$ ratio, $x_\mathrm{J\gamma}$, is measured for pairs with azimuthal opening angle $\Delta\phi > 7\pi/8$. Distributions of the per-photon jet yield as a function of $x_\mathrm{J\gamma}$, $(1/N_\gamma)(\mathrm{d}N/\mathrm{d}x_\mathrm{J\gamma})$, are corrected for detector effects via a two-dimensional unfolding procedure and reported at the particle level. In $pp$ collisions, the distributions are well described by Monte Carlo event generators. In Pb+Pb collisions, the $x_\mathrm{J\gamma}$ distribution is modified from that observed in $pp$ collisions with increasing centrality, consistent with the picture of parton energy loss in the hot nuclear medium. The data are compared with a suite of energy-loss models and calculations.

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Search for pair- and single-production of vector-like quarks in final states with at least one $Z$ boson decaying into a pair of electrons or muons in $pp$ collision data collected with the ATLAS detector at $\sqrt{s} = 13$ TeV

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Phys.Rev. D98 (2018) 112010, 2018.
Inspire Record 1679959 DOI 10.17182/hepdata.83660

A search for vector-like quarks is presented, which targets their decay into a $Z$ boson and a third-generation Standard Model quark. In the case of a vector-like quark $T$ ($B$) with charge $+2/3e$ ($-1/3e$), the decay searched for is $T \rightarrow Zt$ ($B \rightarrow Zb$). Data for this analysis were taken during 2015 and 2016 with the ATLAS detector at the Large Hadron Collider and correspond to 36.1 fb$^{-1}$ of $pp$ collisions at $\sqrt{s} = 13$ TeV. The final state used is characterized by the presence of a $Z$ boson with high transverse momentum, which is reconstructed from a pair of opposite-sign same-flavor leptons, as well as $b$-tagged jets. Pair- and single-production of vector-like quarks are both taken into account and are each searched for using optimized dileptonic exclusive and trileptonic inclusive event selections. In these selections, the high scalar sum of jet transverse momenta, the presence of high-transverse-momentum large-radius jets, as well as - in the case of the single-production selections - the presence of forward jets are used. No significant excess over the background-only hypothesis is found and exclusion limits at 95% confidence level allow masses of vector-like quarks of $m_T > 1030$ GeV ($m_T > 1210$ GeV) and $m_B > 1010$ GeV ($m_B > 1140$ GeV) in the singlet (doublet) model. In the case of 100% branching ratio for $T\rightarrow Zt$ ($B\rightarrow Zb$), the limits are $m_T > 1340$ GeV ($m_B > 1220$ GeV). Limits at 95% confidence level are also set on the coupling to Standard Model quarks for given vector-like quark masses.

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Observed upper limits at 95$\%$ CL on the cross section times BR to $Zt$ as a function of the vector-like $T$-quark mass and coupling $\kappa_T$ for the combination of the SP $2\ell$ and SP $\geq 3\ell$ channels.

Signal cutflows for the $B\bar B$ process in the singlet model in the PP $2\ell$ $0-1$J channel in the 0-large-$R$ jet SR. Only statistical uncertainties are shown.

Signal cutflows for the $B\bar B$ process in the singlet model in the PP $2\ell$ $0-1$J channel in the 1-large-$R$ jet SR. Only statistical uncertainties are shown.

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Measurements of the Higgs boson production and decay rates and constraints on its couplings from a combined ATLAS and CMS analysis of the LHC pp collision data at $ \sqrt{s}=7 $ and 8 TeV

The ATLAS & CMS collaborations Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
JHEP 1608 (2016) 045, 2016.
Inspire Record 1468068 DOI 10.17182/hepdata.78403

Combined ATLAS and CMS measurements of the Higgs boson production and decay rates, as well as constraints on its couplings to vector bosons and fermions, are presented. The combination is based on the analysis of five production processes, namely gluon fusion, vector boson fusion, and associated production with a W or a Z boson or a pair of top quarks, and of the six decay modes H → ZZ, W W , γγ, ττ, bb, and μμ. All results are reported assuming a value of 125.09 GeV for the Higgs boson mass, the result of the combined measurement by the ATLAS and CMS experiments. The analysis uses the CERN LHC proton-proton collision data recorded by the ATLAS and CMS experiments in 2011 and 2012, corresponding to integrated luminosities per experiment of approximately 5 fb$^{−1}$ at $ \sqrt{s}=7 $ TeV and 20 fb$^{−1}$ at $ \sqrt{s}=8 $ TeV. The Higgs boson production and decay rates measured by the two experiments are combined within the context of three generic parameterisations: two based on cross sections and branching fractions, and one on ratios of coupling modifiers. Several interpretations of the measurements with more model-dependent parameterisations are also given. The combined signal yield relative to the Standard Model prediction is measured to be 1.09 ± 0.11. The combined measurements lead to observed significances for the vector boson fusion production process and for the H → ττ decay of 5.4 and 5.5 standard deviations, respectively. The data are consistent with the Standard Model predictions for all parameterisations considered.

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Measurement of the azimuthal anisotropy of charged particles produced in $\sqrt{s_{_\text {NN}}}$ = 5.02 TeV Pb+Pb collisions with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Eur.Phys.J. C78 (2018) 997, 2018.
Inspire Record 1686834 DOI 10.17182/hepdata.84427

Measurements of the azimuthal anisotropy in lead–lead collisions at $\sqrt{s_{_\text {NN}}}$ = 5.02 TeV are presented using a data sample corresponding to 0.49 ${\mathrm {nb}}^{-1}$ integrated luminosity collected by the ATLAS experiment at the LHC in 2015. The recorded minimum-bias sample is enhanced by triggers for “ultra-central” collisions, providing an opportunity to perform detailed study of flow harmonics in the regime where the initial state is dominated by fluctuations. The anisotropy of the charged-particle azimuthal angle distributions is characterized by the Fourier coefficients, $v_{2}$ – $v_{7}$ , which are measured using the two-particle correlation, scalar-product and event-plane methods. The goal of the paper is to provide measurements of the differential as well as integrated flow harmonics $v_{n}$ over wide ranges of the transverse momentum, 0.5  $<p_{\mathrm{T}}<$  60 GeV, the pseudorapidity, $|\eta |<$  2.5, and the collision centrality 0–80%. Results from different methods are compared and discussed in the context of previous and recent measurements in Pb+Pb collisions at $\sqrt{s_{_\text {NN}}}$ = 2.76  $\mathrm{TeV}$ and 5.02  $\mathrm{TeV}$ . In particular, the shape of the $p_{\mathrm{T}}$ dependence of elliptic or triangular flow harmonics is observed to be very similar at different centralities after scaling the $v_{n}$ and $p_{\mathrm{T}}$ values by constant factors over the centrality interval 0–60% and the $p_{\mathrm{T}}$ range 0.5  $< p_{\mathrm{T}}<$  5 GeV.

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The V2 harmonic measured with the scalar product method as a funtion of transverse momentum in centrality bin 0-0.1%

The V2 harmonic measured with the scalar product method as a funtion of transverse momentum in centrality bin 0-1%

The V2 harmonic measured with the scalar product method as a funtion of transverse momentum in centrality bin 0-5%