A search for flavour-changing neutral current decays of a top quark into an up-type quark (q = u, c) and the Standard Model Higgs boson, t Hq, is presented. The search is based on a dataset of pp collisions at = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 36.1 fb(-1). Two complementary analyses are performed to search for top-quark pair events in which one top quark decays into Wb and the other top quark decays into Hq, and target the Hbb and H (+-) decay modes, respectively. The high multiplicity of b-quark jets, or the presence of hadronically decaying -leptons, is exploited in the two analyses respectively. Multivariate techniques are used to separate the signal from the background, which is dominated by top-quark pair production. No significant excess of events above the background expectation is found, and 95% CL upper limits on the t Hq branching ratios are derived. The combination of these searches with ATLAS searches in diphoton and multilepton final states yields observed (expected) 95% CL upper limits on the t Hc and t Hu branching ratios of 1.1 x 10(-3) (8.3 x 10(-4)) and 1.2 x 10(-3) (8.3 x 10(-4)), respectively. The corresponding combined observed (expected) upper limits on the |(tcH)| and |(tuH)| couplings are 0.064 (0.055) and 0.066 (0.055), respectively.

Search for top-quark decays t -> Hq with 36 fb(-1) of pp collision data at root s=13 TeV with the ATLAS detector / Aaboud, M., Aad, G., Abbott, B., Abdinov, O., Abeloos, B., Abhayasinghe, D.K., Abidi, S.H., Abouzeid, O.S., Abraham, N.L., Abramowicz, H., Abreu, H., Abulaiti, Y., Acharya, B.S., Adachi, S., Adamczyk, L., Adelman, J., Adersberger, M., Adiguzel, A., Adye, T., Affolder, A.A., et al.. - In: INTERNATIONAL JOURNAL OF HIGH ENERGY PHYSICS. - ISSN 2376-7448. - 5(2019). [10.1007/JHEP05(2019)123]

Search for top-quark decays t -> Hq with 36 fb(-1) of pp collision data at root s=13 TeV with the ATLAS detector

Artoni, G.;Bagnaia, P.;Betti, A.;Bini, C.;De Cecco, S.;Gentile, S.;Giagu, S.;Kado, M.;Lacava, F.;Luci, C.;Messina, A.;Policicchio, A.;Sebastiani, C. D.;
2019

Abstract

A search for flavour-changing neutral current decays of a top quark into an up-type quark (q = u, c) and the Standard Model Higgs boson, t Hq, is presented. The search is based on a dataset of pp collisions at = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 36.1 fb(-1). Two complementary analyses are performed to search for top-quark pair events in which one top quark decays into Wb and the other top quark decays into Hq, and target the Hbb and H (+-) decay modes, respectively. The high multiplicity of b-quark jets, or the presence of hadronically decaying -leptons, is exploited in the two analyses respectively. Multivariate techniques are used to separate the signal from the background, which is dominated by top-quark pair production. No significant excess of events above the background expectation is found, and 95% CL upper limits on the t Hq branching ratios are derived. The combination of these searches with ATLAS searches in diphoton and multilepton final states yields observed (expected) 95% CL upper limits on the t Hc and t Hu branching ratios of 1.1 x 10(-3) (8.3 x 10(-4)) and 1.2 x 10(-3) (8.3 x 10(-4)), respectively. The corresponding combined observed (expected) upper limits on the |(tcH)| and |(tuH)| couplings are 0.064 (0.055) and 0.066 (0.055), respectively.
2019
Hadron-Hadron scattering (experiments); Rare decay; Top physics; PAIR-PRODUCTION; CROSS-SECTION; STANDARD; HIGGS; BOSON; PROGRAM; MASS
01 Pubblicazione su rivista::01a Articolo in rivista
Search for top-quark decays t -> Hq with 36 fb(-1) of pp collision data at root s=13 TeV with the ATLAS detector / Aaboud, M., Aad, G., Abbott, B., Abdinov, O., Abeloos, B., Abhayasinghe, D.K., Abidi, S.H., Abouzeid, O.S., Abraham, N.L., Abramowicz, H., Abreu, H., Abulaiti, Y., Acharya, B.S., Adachi, S., Adamczyk, L., Adelman, J., Adersberger, M., Adiguzel, A., Adye, T., Affolder, A.A., et al.. - In: INTERNATIONAL JOURNAL OF HIGH ENERGY PHYSICS. - ISSN 2376-7448. - 5(2019). [10.1007/JHEP05(2019)123]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/1306041
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