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). Search for bottom-squark pair production with the ATLAS detector in final states containing Higgs bosons, b-jets and missing transverse momentum. J. High Energy Phys., 12(12), 060–50pp.
Abstract: The result of a search for the pair production of the lightest supersymmetric partner of the bottom quark ((b) over tilde (1)) using 139 fb(-1) of proton-proton data collected at root s = 13 TeV by the ATLAS detector is reported. In the supersymmetric scenarios considered both of the bottom-squarks decay into a b-quark and the second-lightest neutralino, (b) over tilde (1) -> b + (chi) over tilde (0)(2). Each (chi) over tilde (0)(2) is assumed to subsequently decay with 100% branching ratio into a Higgs boson (h) like the one in the Standard Model and the lightest neutralino: (chi) over tilde (0)(2) -> h + (chi) over tilde (0)(1). The (chi) over tilde (0)(1) is assumed to be the lightest supersymmetric particle (LSP) and is stable. Two signal mass configurations are targeted: the first has a constant LSP mass of 60 GeV; and the second has a constant mass difference between the (chi) over tilde (0)(2) and (chi) over tilde (0)(1) of 130 GeV. The final states considered contain no charged leptons, three or more b-jets, and large missing transverse momentum. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered. Limits at the 95% confidence level are placed in the supersymmetric models considered, and bottom-squarks with mass up to 1.5 TeV are excluded.
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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 heavy diboson resonances in semileptonic final states in pp collisions at root s=13 TeV with the ATLAS detector. Eur. Phys. J. C, 80(12), 1165–41pp.
Abstract: This paper reports on a search for heavy resonances decaying into WW, ZZ or WZ using proton-proton collision data at a centre-of-mass energy of integral s = 13TeV. The data, corresponding to an integrated luminosity of 139 fb(1), were recorded with the ATLAS detector from 2015 to 2018 at the Large Hadron Collider. The search is performed for final states in which one W or Z boson decays leptonically, and the other W boson or Z boson decays hadronically. The data are found to be described well by expected backgrounds. Upper bounds on the production cross sections of heavy scalar, vector or tensor resonances are derived in the mass range 300-5000 GeV within the context of Standard Model extensions with warped extra dimensions or including a heavy vector triplet. Production through gluon-gluon fusion, Drell-Yan or vector-boson fusion are considered, depending on the assumed model.
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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). Alignment of the ATLAS Inner Detector in Run 2. Eur. Phys. J. C, 80(12), 1194–41pp.
Abstract: The performance of the ATLAS Inner Detector alignment has been studied using pp collision data at v s = 13 TeV collected by the ATLAS experiment during Run 2 (2015-2018) of the Large Hadron Collider (LHC). The goal of the detector alignment is to determine the detector geometry as accurately as possible and correct for time-dependent movements. The Inner Detector alignment is based on the minimization of track-hit residuals in a sequence of hierarchical levels, from global mechanical assembly structures to local sensors. Subsequent levels have increasing numbers of degrees of freedom; in total there are almost 750,000. The alignment determines detector geometry on both short and long timescales, where short timescales describe movementswithin anLHCfill. The performance and possible track parameter biases originating from systematic detector deformations are evaluated. Momentum biases are studied using resonances decaying to muons or to electrons. The residual sagitta bias and momentum scale bias after alignment are reduced to less than similar to 0.1 TeV-1 and 0.9 x 10(-3), respectively. Impact parameter biases are also evaluated using tracks within jets.
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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 Dark Matter Produced in Association with a Dark Higgs Boson Decaying into (WW -/+)-W-+/- or ZZ in Fully Hadronic Final States from root s=13 TeV pp Collisions Recorded with the ATLAS Detector. Phys. Rev. Lett., 126(12), 121802–21pp.
Abstract: Several extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with VV = (WW -/+)-W-+/- or ZZ pairs from a decay of a dark Higgs boson s is searched for using 139 fb(-1) of pp collisions recorded by the ATLAS detector at a center-of-mass energy of 13 TeV. The s -> V(q (q) over bar )V(q (q) over bar) decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted VV pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with m(s) > 160 GeV are excluded.
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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. (2021). Longitudinal Flow Decorrelations in Xe plus Xe Collisions at root s(NN )=5.44 TeV with the ATLAS Detector. Phys. Rev. Lett., 126(12), 122301–20pp.
Abstract: The first measurement of longitudinal decorrelations of harmonic flow amplitudes v(n) for n = 2-4 in Xe + Xe collisions at root s(NN) = 5.44 TeV is obtained using 3 μb(-1) of data with the ATLAS detector at the LHC. The decorrelation signal for v(3) and v(4) is found to be nearly independent of collision centrality and transverse momentum (p(T)) requirements on fmal-state particles, but for v(2) a strong centrality and p(T) dependence is seen. When compared with the results from Pb + Pb collisions at. root s(NN) = 5.02 TcV, the longitudinal decorrelation signal in midcentral Xe + Xe collisions is found to be larger for v(2), but smaller for v(3). Current hydrodynamic models reproduce the ratios of the v(n) measured in Xe + Xe collisions to those in Pb + Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe + Xe and Pb + Pb. The results on the system-size dependence provide new insights and an important lever arm to separate effects of the longitudinal structure of the initial state from other early and late time effects in heavy-ion collisions.
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