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 photonic signatures of gauge-mediated supersymmetry in 13 TeV pp collisions with the ATLAS detector. Phys. Rev. D, 97(9), 092006–32pp.
Abstract: A search is presented for photonic signatures, motivated by generalized models of gauge-mediated supersymmetry breaking. This search makes use of proton-proton collision data at root s = 13 TeV corresponding to an integrated luminosity of 36.1 fb(-1) recorded by the ATLAS detector at the LHC, and it explores models dominated by both strong and electroweak production of supersymmetric partner states. Experimental signatures incorporating an isolated photon and significant missing transverse momentum are explored. These signatures include events with an additional photon or additional jet activity not associated with any specific underlying quark flavor. No significant excess of events is observed above the Standard Model prediction, and 95% confidence-level upper limits of between 0.083 and 0.32 fb are set on the visible cross section of contributions from physics beyond the Standard Model. These results are interpreted in terms of lower limits on the masses of gluinos, squarks, and gauginos in the context of generalized models of gauge-mediated supersymmetry, which reach as high as 2.3 TeV for strongly produced and 1.3 TeV for weakly produced supersymmetric partner pairs.
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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 the Decay of the Higgs Boson to Charm Quarks with the ATLAS Experiment. Phys. Rev. Lett., 120(21), 211802–20pp.
Abstract: A direct search for the standard model Higgs boson decaying to a pair of charm quarks is presented. Associated production of the Higgs and Z bosons, in the decay mode ZH -> l(+)l(-) cc is studied. A data set with an integrated luminosity of 36.1 fb(-1) of pp collisions at root s = 13 TeV recorded by the ATLAS experiment at the LHC is used. The H -> cc signature is identified using charm-tagging algorithms. The observed (expected) upper limit on sigma(pp -> ZH) x B(H -> cc) is 2.7 (3.9(-2.1)(+2.1) ) pb at the 95% confidence level for a Higgs boson mass of 125 GeV, while the standard model value is 26 fb.
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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 a Structure in the B-s(0) pi(+/-) Invariant Mass Spectrum with the ATLAS Experiment. Phys. Rev. Lett., 120(20), 202007–19pp.
Abstract: A search for the narrow structure, X(5568), reported by the DO Collaboration in the decay sequence X -> B-s(0) pi +/-, B-s(0) -> J/psi phi, is presented. The analysis is based on a data sample recorded with the ATLAS detector at the LHC corresponding to 4.9 fb(-1) of pp collisions at 7 TeV and 19.5 fb(-1)at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by DO, and on the A production rate relative to B-s(0) mesons, rho x, were determined at 95% confidence level. The results are N(X) < 382 and rho x <0.015 for B-s(0) mesons with transverse momenta above 10 GeV and N(X) < 356 and rho(x) < 0.016 for transverse momenta above 15 GeV. Limits are also set for potential B-s(0) pi(+) resonances in the mass range 5550 to 5700 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. (2018). Measurement of differential cross sections and W+/W- cross-section ratios for W boson production in association with jets at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 05(5), 077–60pp.
Abstract: This paper presents a measurement of the W boson production cross section and the W+/W- cross-section ratio, both in association with jets, in proton-proton collisions at root s = 8 TeV with the ATLAS experiment at the Large Hadron Collider. The measurement is performed in final states containing one electron and missing transverse momentum using data corresponding to an integrated luminosity of 20.2 fb(-1). Differential cross sections for events with at least one or two jets are presented for a range of observables, including jet transverse momenta and rapidities, the scalar sum of transverse momenta of the visible particles and the missing transverse momentum in the event, and the transverse momentum of the W boson. For a subset of the observables, the differential cross sections of positively and negatively charged W bosons are measured separately. In the cross-section ratio of W+/W- the dominant systematic uncertainties cancel out, improving the measurement precision by up to a factor of nine. The observables and ratios selected for this paper provide valuable input for the up quark, down quark, and gluon parton distribution functions of the proton.
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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 the standard model Higgs boson produced in association with top quarks and decaying into a b(b)overbar pair in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 97(7), 072016–44pp.
Abstract: A search for the standard model Higgs boson produced in association with a top-quark pair, t(t)overbar H, is presented. The analysis uses 36.1 fb(-1) of pp collision data at root s = 13 TeV collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search targets the H -> b(b)overbar decay mode. The selected events contain either one or two electrons or muons from the top-quark decays, and are then categorized according to the number of jets and how likely these are to contain b-hadrons. Multivariate techniques are used to discriminate between signal and background events, the latter being dominated by ft + jets production. For a Higgs boson mass of 125 GeV, the ratio of the measured t(t)overbarH signal cross-section to the standard model expectation is found to be μ= 0.84(-0.61)(+0.64). A value of μgreater than 2.0 is excluded at 95% confidence level (C.L.) while the expected upper limit is μ< 1.2 in the absence of a t(t)overbar H signal.
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