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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2023). Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ → 4l events with the ATLAS detector at √s=13 TeV. J. High Energy Phys., 12(12), 107–48pp.
Abstract: A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13TeV recorded by the ATLAS detector at the Large Hadron Collider. The ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 +/- 0.60 fb, consistent with the next-to-leadingorder Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.
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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. (2024). Search for pair production of squarks or gluinos decaying via sleptons or weak bosons in final states with two same-sign or three leptons with the ATLAS detector. J. High Energy Phys., 02(2), 107–55pp.
Abstract: A search for pair production of squarks or gluinos decaying via sleptons or weak bosons is reported. The search targets a final state with exactly two leptons with same-sign electric charge or at least three leptons without any charge requirement. The analysed data set corresponds to an integrated luminosity of 139 fb(-1) of proton-proton collisions collected at a centre-of-mass energy of 13TeV with the ATLAS detector at the LHC. Multiple signal regions are defined, targeting several SUSY simplified models yielding the desired final states. A single control region is used to constrain the normalisation of the WZ + jets background. No significant excess of events over the Standard Model expectation is observed. The results are interpreted in the context of several supersymmetric models featuring R-parity conservation or R-parity violation, yielding exclusion limits surpassing those from previous searches. In models considering gluino (squark) pair production, gluino (squark) masses up to 2.2 (1.7) TeV are excluded at 95% confidence level.
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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. (2018). Search for top-squark pair production in final states with one lepton, jets, and missing transverse momentum using 36 fb(-1) of root s=13 TeV pp collision data with the ATLAS detector. J. High Energy Phys., 06(6), 108–96pp.
Abstract: The results of a search for the direct pair production of top squarks, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, several energetic jets, and missing transverse momentum are reported. The analysis also targets spin-0 mediator models, where the mediator decays into a pair of dark-matter particles and is produced in association with a pair of top quarks. The search uses data from proton-proton collisions delivered by the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of root s = 13TeV and recorded by the ATLAS detector, corresponding to an integrated luminosity of 36 fb(-1). A wide range of signal scenarios with different mass-splittings between the top squark, the lightest neutralino and possible intermediate supersymmetric particles are considered, including cases where the W bosons or the top quarks produced in the decay chain are off-shell. No significant excess over the Standard Model prediction is observed. The null results are used to set exclusion limits at 95% confidence level in several supersymmetry benchmark models. For pair-produced top-squarks decaying into top quarks, top-squark masses up to 940 GeV are excluded. Stringent exclusion limits are also derived for all other considered top-squark decay scenarios. For the spin-0 mediator models, upper limits are set on the visible cross-section.
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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). Measurement of the nuclear modification factor for inclusive jets in Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector. Phys. Lett. B, 790, 108–128.
Abstract: Measurements of the yield and nuclear modification factor, R-AA, for inclusive jet production are performed using 0.49 nb(-1) of Pb+Pb data at root s(NN) = 5.02 TeV and 25 pb(-1) of Pb+Pb data at root s = 5.02 TeV with the ATLAS detector at the LHC. Jets are reconstructed with the anti-k(t) algorithm with radius parameter R = 0.4 and are measured over the transverse momentum range of 40-1000 GeV in six rapidity intervals covering vertical bar y vertical bar < 2.8. The magnitude of R-AA increases with increasing jet transverse momentum, reaching a value of approximately 0.6 at 1 TeV in the most central collisions. The magnitude of R-AA also increases towards peripheral collisions. The value of R-AA is independent of rapidity at low jet transverse momenta, but it is observed to decrease with increasing rapidity at high transverse momenta.
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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. (2020). Search for the HH ->b bbar b bbar process via vector-boson fusion production using proton-proton collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 07(7), 108–37pp.
Abstract: A search for Higgs boson pair production via vector-boson fusion (VBF) in the b bbar b bbar final state is carried out with the ATLAS experiment using 126 fb(-1) of proton- proton collision data delivered at root s = 13 TeV by the Large Hadron Collider. This search is sensitive to VBF production of additional heavy bosons that may decay into Higgs boson pairs, and in a non-resonant topology it can constrain the quartic coupling between the Higgs bosons and vector bosons. No significant excess relative to the Standard Model expectation is observed, and limits on the production cross-section are set at the 95% confidence level for a heavy scalar resonance in the context of an extended Higgs sector, and for non-resonant Higgs boson pair production. Interpretation in terms of the coupling between a Higgs boson pair and two vector bosons is also provided: coupling values normalised to the Standard Model expectation of kappa (2V)< -0.76 and <kappa>(2V)> 2.90 are excluded at the 95% confidence level in 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. (2018). Measurement of the W-boson mass in pp collisions at root s=7 TeV with the ATLAS detector. Eur. Phys. J. C, 78(2), 110–61pp.
Abstract: A measurement of the mass of the W boson is presented based on proton-proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding to 4.6 fb(-1) of integrated luminosity. The selected data sample consists of 7.8 x 10(6) candidates in the W -> μnu channel and 5.9 x 10(6) candidates in the W -> e nu channel. The W-boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the W boson transverse mass in the electron and muon decay channels, yielding m(W) = 80370 +/- 7 (stat.) +/- 11(exp. syst.) +/- 14 (mod. syst.) MeV = 80370 +/- 19 MeV, where the first uncertainty is statistical, the second corresponds to the experimental systematic uncertainty, and the third to the physics-modelling systematic uncertainty. A measurement of the mass difference between the W+ and W- bosons yields m(W+) – m(W-) = -29 +/- 28 MeV.
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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). Searches for the Z gamma decay mode of the Higgs boson and for new high-mass resonances in pp collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 10(10), 112–51pp.
Abstract: This article presents searches for the Z gamma decay of the Higgs boson and for narrow high-mass resonances decaying to Z gamma, exploiting Z boson decays to pairs of electrons or muons. The data analysis uses 36.1 fb(-1) of pp collisions at root s = 13 recorded by the ATLAS detector at the CERN Large Hadron Collider. The data are found to be consistent with the expected Standard Model background. The observed (expected – assuming Standard Model pp -> H -> Z gamma production and decay) upper limit on the production cross section times the branching ratio for pp -> H -> Z gamma is 6.6. (5.2) times the Standard Model prediction at the 95% confidence level for a Higgs boson mass of 125.09 GeV. In addition, upper limits are set on the production cross section times the branching ratio as a function of the mass of a narrow resonance between 250 GeV and 2.4 TeV, assuming spin-0 resonances produced via gluon-gluon fusion, and spin-2 resonances produced via gluon-gluon or quark-antiquark initial states. For high-mass spin-0 resonances, the observed (expected) limits vary between 88 fb (61 fb) and 2.8 fb (2.7 fb) for the mass range from 250 GeV to 2.4 TeV at the 95% confidence level.
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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). Search for pairs of scalar leptoquarks decaying into quarks and electrons or muons in root s=13 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 10(10), 112–45pp.
Abstract: A search for new-physics resonances decaying into a lepton and a jet performed by the ATLAS experiment is presented. Scalar leptoquarks pair-produced inppcollisions at root s = 13 TeV at the Large Hadron Collider are considered using an integrated luminosity of 139 fb(-1), corresponding to the full Run 2 dataset. They are searched for in events with two electrons or two muons and two or more jets, including jets identified as arising from the fragmentation ofc- orb-quarks. The observed yield in each channel is consistent with the Standard Model background expectation. Leptoquarks with masses below 1.8 TeV and 1.7 TeV are excluded in the electron and muon channels, respectively, assuming a branching ratio into a charged lepton and a quark of 100%, with minimal dependence on the quark flavour. Upper limits on the aforementioned branching ratio are also given as a function of the leptoquark mass.
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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. (2018). Combined measurement of differential and total cross sections in the H -> gamma gamma and the H -> ZZ* -> 4l decay channels at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 786, 114–133.
Abstract: A combined measurement of differential and inclusive total cross sections of Higgs boson production is performed using 36.1 fb(-1) of 13 TeV proton-proton collision data produced by the LHC and recorded by the ATLAS detector in 2015 and 2016. Cross sections are obtained from measured H -> gamma gamma and H -> ZZ* -> 4l event yields, which are combined taking into account detector efficiencies, resolution, acceptances and branching fractions. The total Higgs boson production cross section is measured to be 57.0(-5.9)(+6.0) (stat.) (+4.0)(-3.3) (syst.) pb, in agreement with the Standard Model prediction. Differential cross-section measurements are presented for the Higgs boson transverse momentum distribution, Higgs boson rapidity, number of jets produced together with the Higgs boson, and the transverse momentum of the leading jet. The results from the two decay channels are found to be compatible, and their combination agrees with the Standard Model predictions.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cantero, J., et al. (2023). Search for dark matter produced in association with a dark Higgs boson decaying into W+W- in the one-lepton final state at root s=13 TeV using 139 fb-1 of pp collisions recorded with the ATLAS detector. J. High Energy Phys., 07(7), 116–49pp.
Abstract: Several extensions of the Standard Model predict the production of dark matter particles at the LHC. A search for dark matter particles produced in association with a dark Higgs boson decaying into W+W- in the l(+/-)nu q (q) over bar' final states with l = e, μis presented. This analysis uses 139 fb(-1) of pp collisions recorded by the ATLAS detector at a centre-of-mass energy of 13TeV. The W-+/- -> q (q) over bar' decays are reconstructed from pairs of calorimeter-measured jets or from track-assisted reclustered jets, a technique aimed at resolving the dense topology from a pair of boosted quarks using jets in the calorimeter and tracking information. The observed data are found to agree with Standard Model predictions. Scenarios with dark Higgs boson masses ranging between 140 and 390 GeV are excluded.
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