ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Search for resonant production of dark quarks in the dijet final state with the ATLAS detector. J. High Energy Phys., 02(2), 128–35pp.
Abstract: This paper presents a search for a new Z' resonance decaying into a pair of dark quarks which hadronise into dark hadrons before promptly decaying back as Standard Model particles. This analysis is based on proton-proton collision data recorded at root s = 13TeV with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to an integrated luminosity of 139 fb(-1). After selecting events containing large-radius jets with high track multiplicity, the invariant mass distribution of the two highest-transverse-momentum jets is scanned to look for an excess above a data-driven estimate of the Standard Model multijet background. No significant excess of events is observed and the results are thus used to set 95% confidence-level upper limits on the production cross-section times branching ratio of the Z' to dark quarks as a function of the Z' mass for various dark-quark scenarios.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo Gimenez, V., et al. (2022). Search for resonant pair production of Higgs bosons in the b(b)over-barb(b)over-bar final state using pp collisions at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 105(9), 092002–36pp.
Abstract: A search for resonant Higgs boson pair production in the b (b) over barb (b) over bar final state is presented. The analysis uses 126 fb(-1)- 139 fb(-1) of pp collision data at root s = 13 TeV collected with the ATLAS detector at the Large Hadron Collider. The analysis is divided into two channels, targeting Higgs boson decays which are reconstructed as pairs of small-radius jets or as individual large-radius jets. Spin-0 and spin2 benchmark signal models are considered, both of which correspond to resonant HH production via gluon-gluon fusion. The data are consistent with Standard Model predictions. Upper limits are set on the production cross section times branching ratio to Higgs boson pairs of a new resonance in the mass range from 251 GeV to 5 TeV.
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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. (2018). Search for Resonant and Nonresonant Higgs Boson Pair Production in the b(b)over-bar tau(+) tau(-) Decay Channel in pp Collisions at root s=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 121(19), 191801–24pp.
Abstract: A search for resonant and nonresonant pair production of Higgs bosons in the b (b) over bar tau(+)tau(-) final state is presented. The search uses 36.1 fb(-1) of pp collision data with root s = 13 TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. Decays of the tau-lepton pairs with at least one tau lepton decaying to final states with hadrons and a neutrino are considered. No significant excess above the expected background is observed in the data. The cross-section times branching ratio for nonresonant Higgs boson pair production is constrained to be less than 30.9 fb, 12.7 times the standard model expectation, at 95% confidence level. The data are also analyzed to probe resonant Higgs boson pair production, constraining a model with an extended Higgs sector based on two doublets and a Randall-Sundrum bulk graviton model. Upper limits are placed on the resonant Higgs boson pair production cross-section times branching ratio, excluding resonances X in the mass range 305 GeV < m(X) < 402 GeV in the simplified hMSSM minimal supersymmetric model for tan beta = 2 and excluding bulk Randall-Sundrum gravitons G(KK) in the mass range 325 GeV < m(GKK) < 885 GeV for k/(M) over bar P-1 = 1.
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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 resonant and non-resonant Higgs boson pair production in the bbτ+τ- decay channel using 13 TeV pp collision data from the ATLAS detector. J. High Energy Phys., 07(7), 040–62pp.
Abstract: A search for Higgs boson pair production in events with two b-jets and two tau -leptons is presented, using a proton-proton collision dataset with an integrated luminosity of 139 fb(-1) collected at root s = 13TeV by the ATLAS experiment at the LHC. Higgs boson pairs produced non-resonantly or in the decay of a narrow scalar resonance in the mass range from 251 to 1600 GeV are targeted. Events in which at least one tau-lepton decays hadronically are considered, and multivariate discriminants are used to reject the backgrounds. No significant excess of events above the expected background is observed in the non-resonant search. The largest excess in the resonant search is observed at a resonance mass of 1 TeV, with a local (global) significance of 3.1 sigma (2.0 sigma). Observed (expected) 95% confidence-level upper limits are set on the non-resonant Higgs boson pair-production cross-section at 4.7 (3.9) times the Standard Model prediction, assuming Standard Model kinematics, and on the resonant Higgs boson pair-production cross-section at between 21 and 900 fb (12 and 840 fb), depending on the mass of the narrow scalar resonance.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., et al. (2018). Search for resonances in the mass distribution of jet pairs with one or two jets identified as b-jets in proton-proton collisions at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 98(3), 032016–24pp.
Abstract: A search for new resonances decaying into jets containing b-hadrons in pp collisions with the ATLAS detector at the LHC is presented in the dijet mass range from 0.57 to 7 TeV. The data set corresponds to an integrated luminosity of up to 36.1 fb(-1) collected in 2015 and 2016 at root s = 13 TeV. No evidence of a significant excess of events above the smooth background shape is found. Upper cross-section limits and lower limits on the corresponding signal mass parameters for several types of signal hypotheses are provided at 95% C.L. In addition, 95% C.L. upper limits are set on the cross sections for new processes that would produce Gaussian-shaped signals in the di-b-jet mass distributions.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Search for resonances decaying into photon pairs in 139 fb(-1) of pp collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 822, 136651–19pp.
Abstract: Searches for new resonances in the diphoton final state, with spin 0 as predicted by theories with an extended Higgs sector and with spin 2 using a warped extra-dimension benchmark model, are presented using 139 fb(-1) of root s = 13 TeV pp collision data collected by the ATLAS experiment at the LHC. No significant deviation from the Standard Model is observed and upper limits are placed on the production cross-section times branching ratio to two photons as a function of the resonance mass.
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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 resonances decaying into a weak vector boson and a Higgs boson in the fully hadronic final state produced in proton – proton collisions at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 102(11), 112008–27pp.
Abstract: A search for heavy resonances decaying into a W or Z boson and a Higgs boson produced in proton – proton collisions at the Large Hadron Collider at root s = 13 TeV is presented. The analysis utilizes the dominant W -> q (q) over bar' or Z -> q (q) over bar and H -> b (b) over bar decays with substructure techniques applied to large-radius jets. A sample corresponding to an integrated luminosity of 139 fb(-1) collected with the ATLAS detector is analyzed and no significant excess of data is observed over the background prediction. The results are interpreted in the context of the heavy vector triplet model with spin-1 W' and Z' bosons. Upper limits on the cross section are set for resonances with mass between 1.5 and 5.0 TeV, ranging from 6.8 to 0.53 fb for W' -> WH and from 8.7 to 0.53 fb for Z' -> ZH 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., Cardillo, F., Castillo, F. L., et al. (2021). Search for R-parity-violating supersymmetry in a final state containing leptons and many jets with the ATLAS experiment using root s=13 TeV proton-proton collision data. Eur. Phys. J. C, 81(11), 1023–39pp.
Abstract: A search for R-parity-violating supersymmetry in final states characterized by high jet multiplicity, at least one isolated light lepton and either zero or at least three b-tagged jets is presented. The search uses 139 fb(-1) of root s = 13 TeV proton-proton collision data collected by the ATLAS experiment during Run 2 of the Large Hadron Collider. The results are interpreted in the context of R-parity-violating supersymmetry models that feature gluino production, top-squark production, or electroweakino production. The dominant sources of background are estimated using a data-driven model, based on observables at medium jet multiplicity, to predict the b-tagged jet multiplicity distribution at the higher jet multiplicities used in the search. Machine-learning techniques are used to reach sensitivity to electroweakino production, extending the data-driven background estimation to the shape of the machine-learning discriminant. No significant excess over the Standard Model expectation is observed and exclusion limits at the 95% confidence level are extracted, reaching as high as 2.4 TeV in gluino mass, 1.35 TeV in top-squark mass, and 320 (365) GeV in higgsino (wino) mass.
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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. (2024). Search for quantum black hole production in lepton plus jet final states using proton-proton collisions at √s=13 TeV with the ATLAS detector. Phys. Rev. D, 109(3), 032010–28pp.
Abstract: A search for quantum black holes in electron + jet and muon + jet invariant mass spectra is performed with 140 fb(-1) of data collected by the ATLAS detector in proton-proton collisions at root s = 13 TeV at the Large Hadron Collider. The observed invariant mass spectrum of lepton + jet pairs is consistent with Standard Model expectations. Upper limits are set at 95% confidence level on the production cross section times branching fractions for quantum black holes decaying into a lepton and a quark in a search region with invariant mass above 2.0 TeV. The resulting quantum black hole lower mass threshold limit is 9.2 TeV in the Arkani-Hamed-Dimopoulos-Dvali model, and 6.8 TeV in the Randall-Sundrum model.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Search for phenomena beyond the Standard Model in events with large b-jet multiplicity using the ATLAS detector at the LHC. Eur. Phys. J. C, 81(1), 11–29pp.
Abstract: A search is presented for new phenomena in events characterised by high jet multiplicity, no leptons (electrons or muons), and four or more jets originating from the fragmentation of b-quarks (b-jets). The search uses 139fb(-1)of s root = 13 TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider during Run 2. The dominant Standard Model background originates from multijet production and is estimated using a data-driven technique based on an extrapolation from events with low b-jet multiplicity to the high b-jet multiplicities used in the search. No significant excess over the Standard Model expectation is observed and 95% confidence-level limits that constrain simplified models of R-parity-violating supersymmetry are determined. The exclusion limits reach 950 GeV in top-squark mass in the models considered.
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