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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(Aad, G. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for the Standard Model Higgs boson decaying into b(b)over-bar produced in association with top quarks decaying hadronically in pp collisions at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 05(5), 160–51pp.
Abstract: A search for Higgs boson production in association with a pair of top quarks (t (t) over barH) is performed, where the Higgs boson decays to b (b) over bar, and both top quarks decay hadronically. The data used correspond to an integrated luminosity of 20.3 fb(-1) of pp collisions at root s = 8 TeV collected with the ATLAS detector at the Large Hadron Collider. The search selects events with at least six energetic jets and uses a boosted decision tree algorithm to discriminate between signal and Standard Model background. The dominant multijet background is estimated using a dedicated data-driven technique. For a Higgs boson mass of 125 GeV, an upper limit of 6.4 (5.4) times the Standard Model cross section is observed (expected) at 95% confidence level. The best-fit value for the signal strength is μ= 1.6 +/- 2.6 times the Standard Model expectation for m(H) = 125 GeV. Combining all t (t) over barH searches carried out by ATLAS at root s = 8 and 7 TeV, an observed (expected) upper limit of 3.1 (1.4) times the Standard Model expectation is obtained at 95% confidence level, with a signal strength μ= 1.7 +/- 0.8.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Study of (W/Z)H production and Higgs boson couplings using H -> WW* decays with the ATLAS detector. J. High Energy Phys., 08(8), 137–65pp.
Abstract: A search for Higgs boson production in association with a W or Z boson, in the H -> WW* decay channel, is performed with a data sample collected with the ATLAS detector at the LHC in proton-proton collisions at centre-of-mass energies root s = 7 TeV and 8TeV, corresponding to integrated luminosities of 4.5 fb(-1) and 20.3 fb(-1), respectively. The W H production mode is studied in two-lepton and three-lepton final states, while twolepton and four-lepton final states are used to search for the ZH production mode. The observed significance, for the combined WH and ZH production, is 2.5 standard deviations while a significance of 0.9 standard deviations is expected in the Standard Model Higgs boson hypothesis. The ratio of the combined W H and Z H signal yield to the Standard Model expectation, mu(VH), is found to be mu(VH) = 3.0(-1.1)(+1.3)(stat.)(-0.7)(+1.0) (sys.) for the Higgs boson mass of 125.36 GeV. The WH and ZH production modes are also combined with the gluon fusion and vector boson fusion production modes studied in the H -> WW* -> l nu l nu decay channel, resulting in an overall observed significance of 6.5 standard deviations and μF-gg+VBF+VH = 1.16(-0.15)(+0.16)(stat.)(-0.15)(+0.18)(sys.). The results are interpreted in terms of scaling factors of the Higgs boson couplings to vector bosons (kappa(V)) and fermions (kappa(F)); the combined results are: vertical bar kappa(V)vertical bar = 1.06(-0.10)(+0.10), vertical bar kappa(F)vertical bar = 0.85(-0.20)(+0.26)
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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. (2016). Search for pair production of Higgs bosons in the bbbb final state using proton-proton collisions at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 94(5), 052002–29pp.
Abstract: A search for Higgs-boson pair production in the bbbb final state is carried out with 3.2 fb(-1) of protonproton collision data collected at root s = 13 TeV with the ATLAS detector. The data are consistent with the estimated background and are used to set upper limits on the production cross section of Higgs-boson pairs times branching ratio to bbbb for both nonresonant and resonant production. In the case of resonant production of Kaluza-Klein gravitons within the Randall-Sundrum model, upper limits in the 24 to 91 fb range are obtained for masses between 600 and 3000 GeV, at the 95% confidence level. The production cross section times branching ratio for nonresonant Higgs-boson pairs is also constrained to be less than 1.22 pb, at the 95% confidence level.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., et al. (2023). Search for high-mass Wγ and Zγ resonances using hadronic W/Z boson decays from 139 fb-1 of pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 07(7), 125–47pp.
Abstract: A search for high-mass charged and neutral bosons decaying to W gamma and Z gamma final states is presented in this paper. The analysis uses a data sample of root s = 13TeV proton-proton collisions with an integrated luminosity of 139 fb(-1) collected by the ATLAS detector during LHC Run 2 operation. The sensitivity of the search is determined using models of the production and decay of spin-1 charged bosons and spin-0/2 neutral bosons. The range of resonance masses explored extends from 1.0TeV to 6.8TeV. At these high resonance masses, it is beneficial to target the hadronic decays of the W and Z bosons because of their large branching fractions. The decay products of the high-momentum W/Z bosons are strongly collimated and boosted-boson tagging techniques are employed to improve the sensitivity. No evidence of a signal above the Standard Model backgrounds is observed, and upper limits on the production cross-sections of these bosons times their branching fractions to W gamma and Z gamma are derived for various boson production models.
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