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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(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2018). Search for pair production of Higgsinos in final states with at least three b-tagged jets in root s=13 TeV pp collisions using the ATLAS detector. Phys. Rev. D, 98(9), 092002–34pp.
Abstract: A search for pair production of the supersymmetric partners of the Higgs boson (higgsinos (H) over tilde) in gaugemediated scenarios is reported. Each higgsino is assumed to decay to a Higgs boson and a gravitino. Two complementary analyses, targeting high- and low-mass signals, are performed to maximize sensitivity. The two analyses utilize LHC pp collision data at a center-of-mass energy root s = 13 TeV, the former with an integrated luminosity of 36.1 fb(-1) and the latter with 24.3 fb(-1), collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing missing transverse momentum and several energetic jets, at least three of which must be identified as b-quark jets. No significant excess is found above the predicted background. Limits on the cross section are set as a function of the mass of the <(Hover tilde> in simplified models assuming production via mass-degenerate higgsinos decaying to a Higgs boson and a gravitino. Higgsinos with masses between 130 and 230 GeV and between 290 and 880 GeV are excluded at the 95% confidence level. Interpretations of the limits in terms of the branching ratio of the higgsino to a Z boson or a Higgs boson are also presented, and a 45% branching ratio to a Higgs boson is excluded for m(<(Hover tilde>) approximate to 400 GeV.
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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). Search for pair production of heavy vectorlike quarks decaying into hadronic final states in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 98(9), 092005–36pp.
Abstract: A search is presented for the pair production of heavy vectorlike quarks, T (T) over bar or B (B) over bar, that decay into final states with jets and no reconstructed leptons. Jets in the final state are classified using a deep neural network as arising from hadronically decaying W/Z bosons, Higgs bosons, top quarks, or background. The analysis uses data from the ATLAS experiment corresponding to 36.1 fb(-1) of proton-proton collisions with a center-of-mass energy of root s = 13 TeV delivered by the Large Hadron Collider in 2015 and 2016. No significant deviation from the Standard Model expectation is observed. Results are interpreted assuming the vectorlike quarks decay into a Standard Model boson and a third-generation-quark, T -> Wb, Ht, Zt or B -> Wt, Hb, Zb, for a variety of branching ratios. At 95% confidence level, the observed (expected) lower limit on the vectorlike B-quark mass for a weak-isospin doublet (B, Y) is 950 (890) GeV, and the lower limits on the masses for the pure decays B -> Hb and T -> Ht, where these results are strongest, arc 1010 (970) GeV and 1010 (1010) GeV, respectively.
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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 Higgs boson pair production in the gamma gamma b(b)over-bar final state with 13 TeV pp collision data collected by the ATLAS experiment. J. High Energy Phys., 11(11), 040–44pp.
Abstract: A search is performed for resonant and non-resonant Higgs boson pair production in the final state. The data set used corresponds to an integrated luminosity of 36.1 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess relative to the Standard Model expectation is observed. The observed limit on the non-resonant Higgs boson pair cross-section is 0.73 pb at 95% confidence level. This observed limit is equivalent to 22 times the predicted Standard Model cross-section. The Higgs boson self-coupling (=(HHH)/SM) is constrained at 95% confidence level to -8.2 < < 13.2. For resonant Higgs boson pair production through , the limit is presented, using the narrow-width approximation, as a function of m(X) in the range 260 GeV < m(X) < 1000 GeV. The observed limits range from 1.1 pb to 0.12 pb over this mass range.
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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). Search for lepton-flavor-violating decays of the Z boson into a r lepton and a light lepton with the ATLAS detector. Phys. Rev. D, 98(9), 092010–31pp.
Abstract: Direct searches for lepton flavor violation in decays of the Z boson with the ATLAS detector at the LHC are presented. Decays of the Z boson into an electron or muon and a hadronically decaying r lepton are considered. The searches are based on a data sample of proton-proton collisions collected by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb(-1) at a center-of-mass energy of root s = 13 TeV. No statistically significant excess of events above the expected background is observed, and upper limits on the branching ratios of lepton-flavor-violating decays are set at the 95% confidence level: B(Z -> e tau) < 5.8 x 10(-5) and B(Z -> μtau) < 2.4 x 10(-5). This is the first limit on B(Z -> e tau) with ATLAS data. The upper limit on 13(Z -> μtau) is combined with a previous ATLAS result based on 20.3 fb(-1) of proton protoncollision data at a center-of-mass energy of root s = 8 TeV and the combined upper limit at 95% confidence level is B(Z -> μtau) < 1.3 x 10(-5).
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