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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Measurements of top-quark pair differential cross-sections in the lepton plus jets channel in pp collisions at root s=13 TeV using the ATLAS detector. J. High Energy Phys., 11(11), 191–69pp.
Abstract: Measurements of differential cross-sections of top-quark pair production in fiducial phase-spaces are presented as a function of top-quark and t (t) over bar system kinematic observables in proton-proton collisions at a centre-of-mass energy of root s = 13TeV. The data set corresponds to an integrated luminosity of 3.2 fb(-1), recorded in 2015 with the ATLAS detector at the CERN Large Hadron Collider. Events with exactly one electron or muon and at least two jets in the final state are used for the measurement. Two separate selections are applied that each focus on different top-quark momentum regions, referred to as resolved and boosted topologies of the t (t) over bar final state. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations by means of calculated chi(2) and p-values.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Measurements of top-quark pair differential cross-sections in the e μchannel in pp collisions at root s=13 TeV using the ATLAS detector. Eur. Phys. J. C, 77(5), 292–30pp.
Abstract: This article presents measurements of t (t) over bar differential cross-sections in a fiducial phase-space region, using an integrated luminosity of 3.2 fb(-1) of proton-proton data at a centre-of-mass energy of root s = 13 TeV recorded by the ATLAS experiment at the LHC in 2015. Differential crosssections are measured as a function of the transverse momentum and absolute rapidity of the top quark, and of the transverse momentum, absolute rapidity and invariant mass of the t (t) over bar system. The t (t) over bar events are selected by requiring one electron and onemuonof opposite electric charge, and at least two jets, one of which must be tagged as containing a b-hadron. The measured differential cross-sections are compared to predictions of next-to-leading order generators matched to parton showers and the measurements are found to be consistent with all models within the experimental uncertainties with the exception of the Powheg-Box + Herwig++ predictions, which differ significantly from the data in both the transverse momentum of the top quark and the mass of the t (t) over bar system.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., et al. (2019). Measurements of top-quark pair differential and double-differential cross-sections in the l plus jets channel with pp collisions at root s=13 TeV using the ATLAS detector. Eur. Phys. J. C, 79(12), 1028–84pp.
Abstract: Single- and double-differential cross-section measurements are presented for the production of top-quark pairs, in the lepton + jets channel at particle and parton level. Two topologies, resolved and boosted, are considered and the results are presented as a function of several kinematic variables characterising the top and t <overline> t system and jet multiplicities. The study was performed using data from pp collisions at centre-of-mass energy of 13 TeV collected in 2015 and 2016 by the ATLAS detector at the CERN Large Hadron Collider (LHC), corresponding to an integrated luminosity of 36 fb-1. Due to the large tt cross-section at the LHC, such measurements allow a detailed study of the properties of top-quark production and decay, enabling precision tests of several Monte Carlo generators and fixed-order Standard Model predictions. Overall, there is good agreement between the theoretical predictions and the data.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). Measurements of top quark spin observables in tt events using dilepton final states in root s=8 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 03(3), 113–50pp.
Abstract: Measurements of top quark spin observables in tt events are presented based on 20.2 fb(-1) of root s = 8TeV 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.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2020). Measurements of the production cross-section for a Z boson in association with b-jets in proton-proton collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 07(7), 044–58pp.
Abstract: This paper presents a measurement of the production cross-section of aZboson in association withb-jets, in proton-proton collisions at root s = 13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 35.6 fb(-1). Inclusive and differential cross-sections are measured for events containing aZboson decaying into electrons or muons and produced in association with at least one or at least two b-jets with transverse momentum p(T)>20 GeV and rapidity vertical bar y vertical bar <2.5. Predictions from several Monte Carlo generators based on leading-order (LO) or next-to-leading-order (NLO) matrix elements interfaced with a parton-shower simulation and testing different flavour schemes for the choice of initial-state partons are compared with measured cross-sections. The 5-flavour number scheme predictions at NLO accuracy agree better with data than 4-flavour number scheme ones. The 4-flavour number scheme predictions underestimate data in events with at least one b-jet.
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