Search for flavor-changing neutral current interactions of the top quark and the Higgs boson decaying to a bottom quark-antiquark pair at $\sqrt{s}$ = 13 TeV

TL;DR

This paper reports a search for rare flavor-changing neutral current interactions between the top quark and the Higgs boson decaying to a bottom quark-antiquark pair, using CMS data at 13 TeV, setting new upper limits on the decay branching fractions.

Contribution

The study introduces a novel analysis using deep neural networks and boosted decision trees to search for top-Higgs FCNC interactions at the LHC, providing the most stringent limits to date.

Findings

No significant excess observed over background.

Upper limits set on top quark decay branching fractions to Higgs and up/charm quarks.

Constraints improve previous bounds on 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 a data sample corresponding to an integrated luminosity of 137 fb$^{-1}$ recorded by the CMS experiment at the LHC in proton-proton collisions at $\sqrt{s}$ = 13 TeV. Events containing exactly one lepton (muon or electron) and at least three jets, among which at least two are identified as originating from the hadronization of a bottom quark, are analyzed. A set of deep neural networks is used for kinematic event reconstruction, while boosted decision trees distinguish the signal from the background events. No significant excess over the background predictions is observed, and upper limits on the signal production cross sections are extracted. These limits are interpreted in terms of top quark decay branching fractions ($\mathcal{B}$) to the Higgs boson and an up (u) or a charm quark (c). Assuming one nonvanishing extra coupling at a time, the observed (expected) upper limits at 95% confidence level are $\mathcal{B}$(t $\to$ Hu) $\lt$ 0.079 (0.11)% and $\mathcal{B}$(t $\to$ Hc) $\lt$ 0.094 (0.086)%.