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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). Fiducial, total and differential cross-section measurements of t-channel single top-quark production in pp collisions at 8 TeV using data collected by the ATLAS detector. Eur. Phys. J. C, 77(8), 531–46pp.
Abstract: Detailed measurements of t-channel single top-quark production are presented. They use 20.2 fb(-1) of data collected by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of 8 TeV at the LHC. Total, fiducial and differential cross-sections are measured for both top-quark and top-antiquark production. The fiducial cross-section is measured with a precision of 5.8% (top quark) and 7.8% (top antiquark), respectively. The total cross-sections are measured to be stot(tq) = 56.7(-3.8)(+4.3) pb for top-quark production and sigma(tot)((t) over barq) = 32.9(-2.7)(+3.0) pb for top-antiquark production, in agreement with the Standard Model prediction. In addition, the ratio of top-quark to top-antiquark production cross-sections is determined to be R-t = 1.72 +/- 0.09. The differential cross-sections as a function of the transverse momentum and rapidity of both the top quark and the top antiquark are measured at both the parton and particle levels. The transverse momentum and rapidity differential cross-sections of the accompanying jet from the t-channel scattering are measured at particle level. All measurements are compared to various Monte Carlo predictions as well as to fixed-order QCD calculations where available.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). The performance of the jet trigger for the ATLAS detector during 2011 data taking. Eur. Phys. J. C, 76(10), 526–47pp.
Abstract: The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided proton-proton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleon-nucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accepted by the trigger if they contain one or more jets above some transverse energy threshold. During 2011 data taking the jet trigger was fully efficient for jets with transverse energy above 25 GeV for triggers seeded randomly at Level 1. For triggers which require a jet to be identified at each of the three trigger levels, full efficiency is reached for offline jets with transverse energy above 60 GeV. Jets reconstructed in the final trigger level and corresponding to offline jets with transverse energy greater than 60 GeV, are reconstructed with a resolution in transverse energy with respect to offline jets, of better than 4 % in the central region and better than 2.5 % in the forward direction.
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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. (2016). Search for TeV-scale gravity signatures in high-mass final states with leptons and jets with the ATLAS detector at root s=13 TeV. Phys. Lett. B, 760, 520–537.
Abstract: A search for physics beyond the Standard Model, in final states with at least one high transverse momentum charged lepton (electron or muon) and two additional high transverse momentum leptons or jets, is performed using 3.2 fb (1) of proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015 at root s = 13 TeV. The upper end of the distribution of the scalar sum of the transverse momenta of leptons and jets is sensitive to the production of high-mass objects. No excess of events beyond Standard Model predictions is observed. Exclusion limits are set for models of microscopic black holes with two to six extra dimensions.
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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. (2015). Search for the associated production of the Higgs boson with a top quark pair in multilepton final states with the ATLAS detector. Phys. Lett. B, 749, 519–541.
Abstract: A search for the associated production of the Higgs boson with a top quark pair is performed in multilepton final states using 20.3 fb(-1) of proton-proton collision data recorded by the ATLAS experiment at root s = 8 TeVat the Large Hadron Collider. Five final states, targeting the decays H -> WW*, tau tau, and ZZ*, are examined for the presence of the Standard Model (SM) Higgs boson: two same-charge light leptons (e or mu) without a hadronically decaying tau lepton; three light leptons; two same-charge light leptons with a hadronically decaying tau lepton; four light leptons; and one light lepton and two hadronically decaying tau leptons. No significant excess of events is observed above the background expectation. The best fit for the t (t) over barH production cross section, assuming a Higgs boson mass of 125 GeV, is 2.1(-1.2)(+1.4) times the SM expectation, and the observed (expected) upper limit at the 95% confidence level is 4.7 (2.4) times the SM rate. The p-value for compatibility with the background-only hypothesis is 1.8s; the expectation in the presence of a Standard Model signal is 0.9 sigma.
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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. (2016). Search for supersymmetry in a final state containing two photons and missing transverse momentum in root s=13 TeV pp collisions at the LHC using the ATLAS detector. Eur. Phys. J. C, 76(9), 517–23pp.
Abstract: A search has been made for supersymmetry in a final state containing two photons and missing transverse momentum using the ATLAS detector at the Large Hadron Collider. The search makes use of 3.2 fb-1 of proton-proton collision data collected at a centre-of-mass energy of 13 TeV in 2015. Using a combination of data-driven and Monte-Carlo-based approaches, the Standard Model background is estimated to be 0.27(-0.10)(+0.22) events. No events are observed in the signal region; considering the expected background and its uncertainty, this observation implies a model-independent 95 % CL upper limit of 0.93 fb (3.0 events) on the visible cross section due to physics beyond the Standard Model. In the context of a generalized model of gauge-mediated supersymmetry breaking with a bino-like next-to-lightest super-symmetric particle, this leads to a lower limit of 1650 GeV on the mass of a degenerate octet of gluino states, independent of the mass of the lighter bino-like neutralino.
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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. (2016). Study of the rare decays of B-s(0) and B-0 into muon pairs from data collected during the LHC Run 1 with the ATLAS detector. Eur. Phys. J. C, 76(9), 513–31pp.
Abstract: A study of the decays B-s(0) -> mu(+)mu(-) and B-0 -> mu(+)mu(-) has been performed using data corresponding to an integrated luminosity of 25 fb(-1) of 7 and 8 TeV proton-proton collisions collected with the ATLAS detector during the LHC Run 1. For the B-0 dimuon decay, an upper limit on the branching fraction is set at B(B-0 -> mu(+)mu(-)) < 4.2 x 10(-10) at 95% confidence level. For B-s(0), the branching fraction B(B-s(0) -> mu(+)mu(-)) = (0.9(-0.8)(+1.1)) x 10(-9) is measured. The results are consistent with the Standard Model expectation with a p value of 4.8%, corresponding to 2.0 standard deviations.
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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. (2015). ATLAS Run 1 searches for direct pair production of third-generation squarks at the Large Hadron Collider. Eur. Phys. J. C, 75(10), 510–48pp.
Abstract: This paper reviews and extends searches for the direct pair production of the scalar supersymmetric partners of the top and bottom quarks in proton-proton collisions collected by the ATLAS collaboration during the LHC Run 1. Most of the analyses use 20 fb(-1) of collisions at a centre-of-mass energy of root s = 8 TeV, although in some case an additional 4.7 fb(-1) of collision data at root s = 7 TeV are used. New analyses are introduced to improve the sensitivity to specific regions of the model parameter space. Since no evidence of third-generation squarks is found, exclusion limits are derived by combining several analyses and are presented in both a simplified model framework, assuming simple decay chains, as well as within the context of more elaborate phenomenological supersymmetric models.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2019). Measurements of gluon-gluon fusion and vector-boson fusion Higgs boson production cross-sections in the H -> WW* -> e nu μnu decay channel in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 789, 508–529.
Abstract: Higgs boson production cross-sections in proton-proton collisions are measured in the H -> WW*-> e nu μnu decay channel. The proton-proton collision data were produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb(-1). The product of the H -> WW* branching fraction times the gluon-gluon fusion and vector-boson fusion cross-sections are measured to be 11.4(-1.1)(+1.2)(stat.)(-1.7)(+1.8)(syst.) pb and 0.50(-0.22)(+0.24)(stat.) +/- 0.17(syst.) pb, respectively, in agreement with Standard Model predictions.
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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. (2016). Charged-particle distributions at low transverse momentum in root s=13 TeV pp interactions measured with the ATLAS detector at the LHC. Eur. Phys. J. C, 76(9), 502–22pp.
Abstract: Measurements of distributions of charged particles produced in proton-proton collisions with a centre-of-mass energy of 13 TeV are presented. The data were recorded by the ATLAS detector at the LHC and correspond to an integrated luminosity of 151 μb(-1). The particles are required to have a transverse momentum greater than 100 MeV and an absolute pseudorapidity less than 2.5. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on multiplicity are measured in events containing at least two charged particles satisfying the above kinematic criteria. The results are corrected for detector effects and compared to the predictions from several Monte Carlo event generators.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., Castillo, F. L., et al. (2019). Search for invisible Higgs boson decays in vector boson fusion at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 793, 499–519.
Abstract: We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is an energetic jet pair with invariant mass of O(1) TeVand O(100) GeVmissing transverse momentum. The analysis uses 36.1 fb(-1) of pp collision data at root s = 13 TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125 GeV scalar particle with Standard Model cross sections, the upper limit on the branching fraction of the Higgs boson decay into invisible particles is 0.37 at 95% confidence level where 0.28 was expected. This limit is interpreted in Higgs portal models to set bounds on the wimp-nucleon scattering cross section. We also consider invisible decays of additional scalar bosons with masses up to 3 TeV for which the upper limits on the cross section times branching fraction are in the range of 0.3-1.7 pb.
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