TY - JOUR

T1 - Search for top-quark decays t → Hq with 36 fb−1 of pp collision data at √s = 13 TeV with the ATLAS detector

AU - Collaboration, ATLAS

AU - Barton, A.E.

AU - Bertram, I.A.

AU - Borissov, G.

AU - Bouhova-Thacker, E.V.

AU - Fox, H.

AU - Henderson, R.C.W.

AU - Jones, R.W.L.

AU - Kartvelishvili, V.

AU - Long, R.E.

AU - Love, P.A.

AU - Muenstermann, D.

AU - Parker, A.J.

AU - Smizanska, M.

AU - Tee, A.S.

AU - Walder, J.

AU - Wharton, A.M.

AU - Whitmore, B.W.

PY - 2019/5/31

Y1 - 2019/5/31

N2 - 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 s = 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 H→ bb¯ and H → τ+τ− decay modes, respectively. The high multiplicity of b-quark jets, or the presence of hadronically decaying τ-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 × 10−3 (8.3 × 10−4) and 1.2 × 10−3 (8.3 × 10−4), respectively. The corresponding combined observed (expected) upper limits on the |λtcH| and |λtuH| couplings are 0.064 (0.055) and 0.066 (0.055), respectively.[Figure not available: see fulltext.] © 2019, The Author(s).

AB - 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 s = 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 H→ bb¯ and H → τ+τ− decay modes, respectively. The high multiplicity of b-quark jets, or the presence of hadronically decaying τ-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 × 10−3 (8.3 × 10−4) and 1.2 × 10−3 (8.3 × 10−4), respectively. The corresponding combined observed (expected) upper limits on the |λtcH| and |λtuH| couplings are 0.064 (0.055) and 0.066 (0.055), respectively.[Figure not available: see fulltext.] © 2019, The Author(s).

KW - Hadron-Hadron scattering (experiments)

KW - Rare decay

KW - Top physics

U2 - 10.1007/JHEP05(2019)123

DO - 10.1007/JHEP05(2019)123

M3 - Journal article

VL - 2019

JO - Journal of High Energy Physics

JF - Journal of High Energy Physics

SN - 1029-8479

IS - 5

M1 - 123

ER -