Ajuts: We acknowledge the support of COST, ERC, ERDF, Horizon 2020, and Marie Skłodowska-Curie Actions, European Union and MINECO, Spain and CERCA Programme Generalitat de Catalunya, Spain. ; Silicon pixel detectors are at the core of the current and planned upgrade of the ATLAS experiment at the LHC. Given their close proximity to the interaction point, these detectors will be exposed to an unprecedented amount of radiation over their lifetime. The current pixel detector will receive damage from non-ionizing radiation in excess of 10 1 MeV n/cm, while the pixel detector designed for the high-luminosity LHC must cope with an order of magnitude larger fluence. This paper presents a digitization model incorporating effects of radiation damage to the pixel sensors. The model is described in detail and predictions for the charge collection efficiency and Lorentz angle are compared with collision data collected between 2015 and 2017 (≤ 10 1 MeV n/cm).
Ajuts: We acknowledge the support of COST, ERC, ERDF, Horizon 2020, and Marie Skłodowska-Curie Actions, European Union and MINECO, Spain and CERCA Programme Generalitat de Catalunya, Spain. ; Limits are set on the pair production of scalar leptoquarks, where all possible decays of the leptoquark into a quark (t, b) and a lepton (τ, ν) of the third generation are considered. The limits are presented as a function of the leptoquark mass and the branching ratio into charged leptons for up-type (LQ → tν/bτ) and down-type (LQ → bν/tτ) leptoquarks. Many results are reinterpretations of previously published ATLAS searches. In all cases, LHC proton-proton collision data at a centre-of-mass energy of s = 13 TeV recorded by the ATLAS detector in 2015 and 2016 are used, corresponding to an integrated luminosity of 36.1 fb. Masses below 800 GeV are excluded for both LQ and LQ independently of the branching ratio, with masses below about 1 TeV being excluded for the limiting cases of branching ratios equal to zero or unity.[Figure not available: see fulltext.].
Ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We knowledge the support of MINECO, Spain i COST, ERC, ERDF, Horizon 2020, and Marie Skłodowska-Curie Actions, European Union. Funded by SCOAP3 ; Searches for non-resonant and resonant Higgs boson pair production are performed in the channel with the final state of using 36.1 of proton-proton collision data recorded at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. No significant deviation from the Standard Model prediction is observed. A 95% confidence-level observed upper limit of 7.7 pb is set on the cross section for non-resonant production, while the expected limit is 5.4 pb. A search for a narrow-width resonance X decaying to a pair of Standard Model Higgs bosons HH is performed with the same set of data, and the observed upper limits on range between 40.0 and 6.1 pb for masses of the resonance between 260 and 500 GeV, while the expected limits range between 17.6 and 4.4 pb. When deriving the limits above, the Standard Model branching ratios of the and are assumed.
Ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO, Spain i EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union. Funded by SCOAP3 ; The performance of the missing transverse momentum () reconstruction with the ATLAS detector is evaluated using data collected in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV in 2015. To reconstruct , fully calibrated electrons, muons, photons, hadronically decaying , and jets reconstructed from calorimeter energy deposits and charged-particle tracks are used. These are combined with the soft hadronic activity measured by reconstructed charged-particle tracks not associated with the hard objects. Possible double counting of contributions from reconstructed charged-particle tracks from the inner detector, energy deposits in the calorimeter, and reconstructed muons from the muon spectrometer is avoided by applying a signal ambiguity resolution procedure which rejects already used signals when combining the various contributions. The individual terms as well as the overall reconstructed are evaluated with various performance metrics for scale (linearity), resolution, and sensitivity to the data-taking conditions. The method developed to determine the systematic uncertainties of the scale and resolution is discussed. Results are shown based on the full 2015 data sample corresponding to an integrated luminosity of 3.2 fb−1.
Ajuts: MINECO, Spain i EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union. Funded by SCOAP3. ; A search for the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb of TeV proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of mass-degenerate sleptons.
Ajuts: MINECO, Spain i COST, ERC, ERDF, Horizon 2020, and Marie Skłodowska-Curie Actions, European Union. Funded by SCOAP3 ; Measurements of the azimuthal anisotropy in lead-lead collisions at = 5.02 TeV are presented using a data sample corresponding to 0.49 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, -, 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 over wide ranges of the transverse momentum, 0.5 60 GeV, the pseudorapidity, 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 = 2.76 and 5.02 . In particular, the shape of the dependence of elliptic or triangular flow harmonics is observed to be very similar at different centralities after scaling the and values by constant factors over the centrality interval 0-60% and the range 0.5 5 GeV.
Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO, Spain and EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union and CERCA Programme Generalitat de Catalunya. Funded by SCOAP3. ; The differential cross-section for the production of a W boson in association with a top quark is measured for several particle-level observables. The measurements are performed using of pp collision data collected with the ATLAS detector at the LHC in 2015 and 2016. Differential cross-sections are measured in a fiducial phase space defined by the presence of two charged leptons and exactly one jet matched to a b -hadron, and are normalised with the fiducial cross-section. Results are found to be in good agreement with predictions from several Monte Carlo event generators.
Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO, Spain and EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union and CERCA Programme Generalitat de Catalunya. Funded by SCOAP3. ; A search for neutral heavy resonances is performed in the decay channel using pp collision data corresponding to an integrated luminosity of , collected at a centre-of-mass energy of 13 by the ATLAS detector at the Large Hadron Collider. No evidence of such heavy resonances is found. In the search for production via the quark-antiquark annihilation or gluon-gluon fusion process, upper limits on as a function of the resonance mass are obtained in the mass range between 200 and up to 5 for various benchmark models: a Higgs-like scalar in different width scenarios, a two-Higgs-doublet model, a heavy vector triplet model, and a warped extra dimensions model. In the vector-boson fusion process, constraints are also obtained on these resonances, as well as on a Higgs boson in the Georgi-Machacek model and a heavy tensor particle coupling only to gauge bosons.
We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO, Spain and EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union. Funded by SCOAP3 ; Previous studies have shown that weighted angular moments derived from jet constituents encode the colour connections between partons that seed the jets. This paper presents measurements of two such distributions, the jet-pull angle and jet-pull magnitude, both of which are derived from the jet-pull angular moment. The measurement is performed in events with one leptonically decaying W boson and one hadronically decaying W boson, using of pp collision data recorded by the ATLAS detector at delivered by the Large Hadron Collider. The observables are measured for two dijet systems, corresponding to the colour-connected daughters of the W boson and the two b -jets from the top-quark decays, which are not expected to be colour connected. To allow the comparison of the measured distributions to colour model predictions, the measured distributions are unfolded to particle level, after correcting for experimental effects introduced by the detector. While good agreement can be found for some combinations of predictions and observables, none of the predictions describes the data well across all observables.
Ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO, Spain and EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union and CERCA Programme Generalitat de Catalunya. ; A measurement of and production is presented. It is based on a data sample from Pb+Pb collisions at and pp collisions at recorded by the ATLAS detector at the LHC in 2015, corresponding to an integrated luminosity of and in Pb+Pb and pp, respectively. The measurements of per-event yields, nuclear modification factors, and non-prompt fractions are performed in the dimuon decay channel for GeV in dimuon transverse momentum, and in rapidity. Strong suppression is found in Pb+Pb collisions for both prompt and non-prompt , increasing with event centrality. The suppression of prompt is observed to be stronger than that of , while the suppression of non-prompt is equal to that of the non-prompt within uncertainties, consistent with the expectation that both arise from b -quarks propagating through the medium. Despite prompt and non-prompt arising from different mechanisms, the dependence of their nuclear modification factors on centrality is found to be quite similar.
Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO, Spain and EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union and CERCA Programme Generalitat de Catalunya. Funded by SCOAP3. ; The elliptic flow of prompt and non-prompt was measured in the dimuon decay channel in Pb+Pb collisions at with an integrated luminosity of with the ATLAS detector at the LHC. The prompt and non-prompt signals are separated using a two-dimensional simultaneous fit of the invariant mass and pseudo-proper decay time of the dimuon system from the decay. The measurement is performed in the kinematic range of dimuon transverse momentum and rapidity , , and 0-60% collision centrality. The elliptic flow coefficient, , is evaluated relative to the event plane and the results are presented as a function of transverse momentum, rapidity and centrality. It is found that prompt and non-prompt mesons have non-zero elliptic flow. Prompt decreases as a function of , while for non-prompt it is, with limited statistical significance, consistent with a flat behaviour over the studied kinematic region. There is no observed dependence on rapidity or centrality.
Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO, Spain and EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union and CERCA Programme Generalitat de Catalunya. Funded by SCOAP3 ; A search for heavy resonances decaying into a pair of bosons leading to and final states, where stands for either an electron or a muon, is presented. The search uses proton-proton collision data at a centre-of-mass energy of 13 corresponding to an integrated luminosity of 36.1 collected with the ATLAS detector during 2015 and 2016 at the Large Hadron Collider. Different mass ranges for the hypothetical resonances are considered, depending on the final state and model. The different ranges span between 200 and 2000 . The results are interpreted as upper limits on the production cross section of a spin-0 or spin-2 resonance. The upper limits for the spin-0 resonance are translated to exclusion contours in the context of Type-I and Type-II two-Higgs-doublet models, while those for the spin-2 resonance are used to constrain the Randall-Sundrum model with an extra dimension giving rise to spin-2 graviton excitations.
Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO, Spain and EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union and CERCA Programme Generalitat de Catalunya. ; A search for the direct production of charginos and neutralinos in final states with at least two hadronically decaying tau leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of 36.1 fb, recorded with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of pair production and of and production in simplified models where the neutralinos and charginos decay solely via intermediate left-handed staus and tau sneutrinos, and the mass of the state is set to be halfway between the masses of the and the . Chargino masses up to 630 GeV are excluded at 95% confidence level in the scenario of direct production of for a massless . Common and masses up to 760 GeV are excluded in the case of production of and assuming a massless . Exclusion limits for additional benchmark scenarios with large and small mass-splitting between the and the are also studied by varying the mass between the masses of the and the .
Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO, Spain and EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union and CERCA Programme Generalitat de Catalunya. Funded by SCOAP3. ; Measurements of longitudinal flow correlations are presented for charged particles in the pseudorapidity range using 7 and 470 of Pb+Pb collisions at and 5.02 TeV, respectively, recorded by the ATLAS detector at the LHC. It is found that the correlation between the harmonic flow coefficients measured in two separated intervals does not factorise into the product of single-particle coefficients, and this breaking of factorisation, or flow decorrelation, increases linearly with the separation between the intervals. The flow decorrelation is stronger at 2.76 TeV than at 5.02 TeV. Higher-order moments of the correlations are also measured, and the corresponding linear coefficients for the -moment of the are found to be proportional to k for , but not for . The decorrelation effect is separated into contributions from the magnitude of and the event-plane orientation, each as a function of . These two contributions are found to be comparable. The longitudinal flow correlations are also measured between of different order in n. The decorrelations of and are found to be independent of each other, while the decorrelations of and are found to be driven by the nonlinear contribution from and , respectively.
Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO, Spain and EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union and CERCA Programme Generalitat de Catalunya. Funded by SCOAP3. ; This paper presents a measurement of the polarisation of leptons produced in decays which is performed with a dataset of proton-proton collisions at TeV, corresponding to an integrated luminosity of 20.2 fb recorded with the ATLAS detector at the LHC in 2012. The decays are reconstructed from a hadronically decaying lepton with a single charged particle in the final state, accompanied by a lepton that decays leptonically. The polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The polarisation extracted over the full phase space within the mass range of 66 116 GeV is found to be . It is in agreement with the Standard Model prediction of , which is obtained from the ALPGEN event generator interfaced with the PYTHIA 6 parton shower modelling and the TAUOLA decay library.
