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

dc.contributor.authorAaboud, M.
dc.contributor.authorAad, G.
dc.contributor.authorAbbott, B.
dc.contributor.authorAbbott, D.C.
dc.contributor.authorAbdinov, O.
dc.contributor.authorAbeloos, B.
dc.contributor.authorAbhayasinghe, D.K.
dc.contributor.authorAbidi, S.H.
dc.contributor.authorAbouZeid, O.S.
dc.contributor.authorAbraham, N.L.
dc.contributor.authorAlbert, Justin
dc.contributor.authorAnelli, Christopher R.
dc.contributor.authorChiu, Y. H.
dc.contributor.authorGhasemi Bostanabad, M.
dc.contributor.authorHamano, Kenji
dc.contributor.authorHill, Ewan Chin
dc.contributor.authorKeeler, Richard
dc.contributor.authorKowalewski, Robert
dc.contributor.authorLefebvre, Michel
dc.contributor.authoret al.
dc.description.abstractA 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.en_US
dc.description.sponsorshipWe thank CERN for the very successful operation of the LHC, as well as the support sta from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS, CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZ S, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, CANARIE, CRC and Compute Canada, Canada; COST, ERC, ERDF, Horizon 2020, and Marie Sk lodowska-Curie Actions, European Union;Investissements d' Avenir Labex and Idex, ANR, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co- nanced by EU-ESF and the Greek NSRF, Greece; BSF-NSF and GIF, Israel; CERCA Programme Generalitat de Catalunya, Spain; The Royal Society and Leverhulme Trust, United Kingdom. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (U.K.) and BNL (U.S.A.), the Tier-2 facilities worldwide and large non-WLCG resource providers. Major contributors of computing resources are listed in ref.en_US
dc.identifier.citationAaboud, M., Aad, G., Abbott, B., Abbot, D. C., Abdinbov, O., Abeloos, B., … Zwalinksi, L. (2019). Search for top-quark decays t → Hq with 36 fb−1 of pp collision data at s√s = 13 TeV with the ATLAS detector. Journal of High Energy Physics, 2019(5).
dc.publisherJournal of High Energy Physicsen_US
dc.subjectHadron-Hadron scattering (experiments)en_US
dc.subjectRare decayen_US
dc.subjectRare decayen_US
dc.titleSearch for top-quark decays t → Hq with 36 fb−1 of pp collision data at s√ = 13 TeV with the ATLAS detectoren_US


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