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

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Issue Date
2019-05-21Author
Aaboud, M.
Rogan, Christopher
The ATLAS collaboration
Publisher
Springer Verlag
Type
Article
Article Version
Scholarly/refereed, publisher version
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Copyright CERN, for the benefit of the ATLAS Collaboration.
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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.
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This work is licensed under a Creative Commons Attribution 4.0 International License.
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Citation
The ATLAS collaboration., Aaboud, M., Aad, G. et al. Search for top-quark decays t → Hq with 36 fb−1 of pp collision data at √𝑠 = 13 TeV with the ATLAS detector. J. High Energ. Phys. 2019, 123 (2019). https://doi.org/10.1007/JHEP05(2019)123
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