Search for the flavor-changing neutral current interactions of the top quark and the Higgs boson which decays into a pair of b quarks at $\sqrt{s}=$ 13 TeV

TL;DR

This paper reports a search for flavor-changing neutral current interactions involving the top quark and Higgs boson decaying into b quarks at 13 TeV, setting upper limits on rare decay branching fractions.

Contribution

It presents the first combined search for FCNC in top-Higgs interactions at 13 TeV, providing new upper limits on top quark decay branching fractions to uH and cH.

Findings

No significant excess over background observed.

Upper limits set on top quark FCNC decay branching fractions.

Constraints improve previous bounds on top-Higgs FCNC interactions.

Abstract

A search for flavor-changing neutral currents (FCNC) in events with the top quark and the Higgs boson is presented. The Higgs boson decay to a pair of b quarks is considered. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$ recorded by the CMS experiment at the LHC in proton-proton collisions at $\sqrt{s}=$ 13 TeV. Two channels are considered: single top quark FCNC production in association with the Higgs boson (pp $\to$ tH), and top quark pair production with FCNC decay of the top quark (t $\to$ qH). Final states with one isolated lepton and at least three reconstructed jets, among which at least two are associated with b quarks, are studied. No significant deviation is observed from the predicted background. Observed (expected) upper limits at 95% confidence level are set on the branching fractions of top quark decays, $\mathcal{B}$(t $\to$ uH) $<$ 0.47% (0.34%) and $\mathcal{B}$(t $\to$ cH) $<$ 0.47% (0.44%), assuming a single nonzero FCNC coupling.