Search for flavor-changing neutral current interactions of the top quark mediated by a Higgs boson in proton-proton collisions at 13 TeV

TL;DR

This paper reports a search for rare flavor-changing neutral current interactions between top quarks and Higgs bosons in proton-proton collisions at 13 TeV, setting new upper limits on the decay probabilities of top quarks to Higgs and lighter quarks.

Contribution

It presents the most stringent limits to date on top-Higgs flavor-changing neutral currents by combining multiple CMS analyses at 13 TeV.

Findings

No significant excess observed above background.

Upper limits on branching fractions are set at 0.019% for t→Hu and 0.037% for t→Hc.

Results improve previous constraints on top-Higgs FCNC interactions.

Abstract

A search for flavor-changing neutral current interactions of the top quark (t) and the Higgs boson (H) is presented. The search is based on proton-proton collision data collected in 2016-2018 at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, and corresponding to an integrated luminosity of 138 fb$^{-1}$. Events containing a pair of leptons with the same-sign electric charge and at least one jet are considered. The results are used to constrain the branching fraction ($\mathcal{B}$) of the top quark decaying to a Higgs boson and an up (u) or charm (c) quark. No significant excess above the estimated background was found. The observed (expected) upper limits at 95% confidence level are found to be 0.072% (0.059%) for $\mathcal{B}$(t $\to$ Hu) and 0.043% (0.062%) for $\mathcal{B}$(t $\to$ Hc). These results are combined with two other searches performed by the CMS Collaboration for flavor-changing neutral current interactions of top quarks and Higgs bosons in final states where the Higgs boson decays to either a pair of photons or a pair of bottom quarks. The resulting observed (expected) upper limits at 95% confidence level are 0.019% (0.027%) for $\mathcal{B}$(t $\to$ Hu) and 0.037% (0.035%) for $\mathcal{B}$(t $\to$ Hc).