ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2017). High-E-T isolated-photon plus jets production in pp collisions at root s=8 TeV with the ATLAS detector. Nucl. Phys. B, 918, 257–316.
Abstract: The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 20.2 fb(-1). Measurements of isolated-photon plus jets cross sections are presented as functions of the photon and jet transverse momenta. The cross sections as functions of the azimuthal angle between the photon and the jets, the azimuthal angle between the jets, the photon-jet invariant mass and the scattering angle in the photon-jet centre-of-mass system are presented. The pattern of QCD radiation around the photon and the leading jet is investigated by measuring jet production in an annular region centred on each object; enhancements are observed around the leading jet with respect to the photon in the directions towards the beams. The experimental measurements are compared to several different theoretical calculations, and overall a good description of the data is found.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2012). Hunt for new phenomena using large jet multiplicities and missing transverse momentum with ATLAS in 4.7fb(-1) of root s=7 TeV proton-proton collisions. J. High Energy Phys., 07(7), 167–40pp.
Abstract: Results are presented of a search for new particles decaying to large numbers of jets in association with missing transverse momentum, using 4.7 fb(-1) of pp collision data at root s = 7 TeV collected by the ATLAS experiment at the Large Hadron Collider in 2011. The event selection requires missing transverse momentum, no isolated electrons or muons, and from >= 6 to >= 9 jets. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a MSUGRA/CMSSM supersymmetric model, where, for large universal scalar mass m(0), gluino masses smaller than 840 GeV are excluded at the 95% confidence level, extending previously published limits. Within a simplified model containing only a gluino octet and a neutralino, gluino masses smaller than 870 GeV are similarly excluded for neutralino masses below 100 GeV.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2015). Identification and energy calibration of hadronically decaying tau leptons with the ATLAS experiment in pp collisions at root s=8 TeV. Eur. Phys. J. C, 75(7), 303–33pp.
Abstract: This paper describes the trigger and offline reconstruction, identification and energy calibration algorithms for hadronic decays of tau leptons employed for the data collected from pp collisions in 2012 with the ATLAS detector at the LHC center-of-mass energy root s = 8 TeV. The performance of these algorithms is measured in most cases with Z decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fb(-1). An uncertainty on the offline reconstructed tau energy scale of 2-4%, depending on transverse energy and pseudorapidity, is achieved using two independent methods. The offline tau identification efficiency is measured with a precision of 2.5% for hadronically decaying tau leptons with one associated track, and of 4% for the case of three associated tracks, inclusive in pseudorapidity and for a visible transverse energy greater than 20 GeV. For hadronic tau lepton decays selected by offline algorithms, the tau trigger identification efficiency is measured with a precision of 2-8%, depending on the transverse energy. The performance of the tau algorithms, both offline and at the trigger level, is found to be stable with respect to the number of concurrent proton-proton interactions and has supported a variety of physics results using hadronically decaying tau leptons at ATLAS.
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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). Identification and rejection of pile-up jets at high pseudorapidity with the ATLAS detector. Eur. Phys. J. C, 77(9), 580–32pp.
Abstract: The rejection of forward jets originating from additional proton-proton interactions (pile-up) is crucial for a variety of physics analyses at the LHC, including Standard Model measurements and searches for physics beyond the Standard Model. The identification of such jets is challenging due to the lack of track and vertex information in the pseudorapidity range vertical bar eta vertical bar > 2.5. This paper presents a novel strategy for forward pile-up jet tagging that exploits jet shapes and topological jet correlations in pile-up interactions. Measurements of the per-jet tagging efficiency are presented using a data set of 3.2 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13 TeV collected with the ATLAS detector. The fraction of pile-up jets rejected in the range 2.5 < vertical bar eta vertical bar < 4.5 is estimated in simulated events with an average of 22 interactions per bunch-crossing. It increases with jet transverse momentum and, for jets with transverse momentum between 20 and 50 GeV, it ranges between 49% and 67% with an efficiency of 85% for selecting hard-scatter jets. A case study is performed in Higgs boson production via the vector-boson fusion process, showing that these techniques mitigate the background growth due to additional proton-proton interactions, thus enhancing the reach for such signatures.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., et al. (2019). Identification of boosted Higgs bosons decaying into b-quark pairs with the ATLAS detector at 13 TeV. Eur. Phys. J. C, 79(10), 836–38pp.
Abstract: This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, H -> b (b) over bar, for proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy root s = 13 TeV. These decays are reconstructed from calorimeter jets found with the anti-k(t) R = 1.0 jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of R = 0.2 track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb(-1) of data collected in 2015 and 2016 using g -> b (b) over bar and Z(-> b (b) over bar)gamma event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2016). Identification of boosted, hadronically decaying W bosons and comparisons with ATLAS data taken at root s=8 TeV. Eur. Phys. J. C, 76(3), 154–47pp.
Abstract: This paper reports a detailed study of techniques for identifying boosted, hadronically decaying W bosons using 20.3 fb(-1) of proton-proton collision data collected by the ATLAS detector at the LHC at a centre-of-mass energy root s = 8 TeV. A range of techniques for optimising the signal jet mass resolution are combined with various jet substructure variables. The results of these studies in Monte Carlo simulations show that a simple pairwise combination of groomed jet mass and one substructure variable can provide a 50 % efficiency for identifying W bosons with transverse momenta larger than 200 GeV while maintaining multijet background efficiencies of 2-4% for jets with the same transverse momentum. These signal and background efficiencies are confirmed in data for a selection of tagging techniques.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2016). Identification of high transverse momentum top quarks in pp collisions at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 06(6), 093–81pp.
Abstract: This paper presents studies of the performance of several jet-substructure techniques, which are used to identify hadronically decaying top quarks with high transverse momentum contained in large-radius jets. The efficiency of identifying top quarks is measured using a sample of top-quark pairs and the rate of wrongly identifying jets from other quarks or gluons as top quarks is measured using multijet events collected with the ATLAS experiment in 20.3 fb(-1) of 8TeV proton-proton collisions at the Large Hadron Collider. Predictions from Monte Carlo simulations are found to provide an accurate description of the performance. The techniques are compared in terms of signal efficiency and background rejection using simulations, covering a larger range in jet transverse momenta than accessible in the dataset. Additionally, a novel technique is developed that is optimized to reconstruct top quarks in events with many jets.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Improved luminosity determination in pp collisions at root s=7 TeV using the ATLAS detector at the LHC. Eur. Phys. J. C, 73(8), 2518–39pp.
Abstract: The luminosity calibration for the ATLAS detector at the LHC during pp collisions at root s = 7 TeV in 2010 and 2011 is presented. Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at root s = 7 TeV. A luminosity uncertainty of delta L/L = +/- 3.5 % is obtained for the 47 pb(-1) of data delivered to ATLAS in 2010, and an uncertainty of delta L/L = +/- 1.8 % is obtained for the 5.5 fb(-1) delivered in 2011.
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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. (2019). In situ calibration of large-radius jet energy and mass in 13 TeV proton-proton collisions with the ATLAS detector. Eur. Phys. J. C, 79(2), 135–42pp.
Abstract: The response of the ATLAS detector to large-radius jets is measured in situ using 36.2 fb(-1) of root s = 13 TeV proton-proton collisions provided by the LHC and recorded by the ATLAS experiment during 2015 and 2016. The jet energy scale is measured in events where the jet recoils against a reference object, which can be either a calibrated photon, a reconstructed Z boson, or a system of well-measured small-radius jets. The jet energy resolution and a calibration of forward jets are derived using dijet balance measurements. The jet mass response is measured with two methods: using mass peaks formed by W bosons and top quarks with large transverse momenta and by comparing the jet mass measured using the energy deposited in the calorimeter with that using the momenta of charged-particle tracks. The transverse momentum and mass responses in simulations are found to be about 2-3% higher than in data. This difference is adjusted for with a correction factor. The results of the different methods are combined to yield a calibration over a large range of transverse momenta (p(T)). The precision of the relative jet energy scale is 1-2% for 200 GeV < p(T) < TeV, while that of the mass scale is 2-10%. The ratio of the energy resolutions in data and simulation is measured to a precision of 10-15% over the same p(T) range.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Inclusive and differential cross-sections for dilepton ttbar production measured in √s=13 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 07(7), 141–78pp.
Abstract: Differential and double-differential distributions of kinematic variables of leptons from decays of top-quark pairs (t (t) over bar) are measured using the full LHC Run 2 data sample collected with the ATLAS detector. The data were collected at a pp collision energy of root s = 13TeV and correspond to an integrated luminosity of 140 fb(-1). The measurements use events containing an oppositely charged e μpair and b-tagged jets. The results are compared with predictions from several Monte Carlo generators. While no prediction is found to be consistent with all distributions, a better agreement with measurements of the lepton p(T) distributions is obtained by reweighting the t (t) over bar sample so as to reproduce the top-quark p(T) distribution from an NNLO calculation. The inclusive top-quark pair production cross-section is measured as well, both in a fiducial region and in the full phase-space. The total inclusive cross-section is found to be sigma(t (t) over bar) = 829 +/- 1 (stat) +/- 13 (syst) +/- 8 (lumi) +/- 2 (beam) pb, where the uncertainties are due to statistics, systematic effects, the integrated luminosity and the beam energy. This is in excellent agreement with the theoretical expectation.
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