Search for charged-lepton flavor violation in top quark production and decay in pp collisions at $\sqrt{s} =$ 13 TeV

TL;DR

This paper reports a search for charged-lepton flavor violation in top quark production and decay at the LHC, setting new upper limits on the branching fractions for these rare processes using CMS data.

Contribution

It introduces the first search for CLFV interactions in top quarks at 13 TeV, using an effective field theory approach to set limits on various interaction types.

Findings

No significant excess observed over the standard model.

Set upper limits on top quark CLFV branching fractions at 95% confidence level.

Established constraints on vector, scalar, and tensor CLFV interactions.

Abstract

Results are presented from a search for charged-lepton flavor violating (CLFV) interactions in top quark production and decay in pp collisions at a center-of-mass energy of 13 TeV. The events are required to contain one oppositely charged electron-muon pair in the final state, along with at least one jet identified as originating from a bottom quark. The data correspond to an integrated luminosity of 138 fb$^{-1}$, collected by the CMS experiment at the LHC. This analysis includes both the production (q $\to$ e$\mu$t) and decay (t $\to$ e$\mu$q) modes of the top quark through CLFV interactions, with q referring to a u or c quark. These interactions are parametrized using an effective field theory approach. With no significant excess over the standard model expectation, the results are interpreted in terms of vector-, scalar-, and tensor-like CLFV four-fermion effective interactions. Finally, observed exclusion limits are set at 95% confidence levels on the respective branching fractions of a top quark to an e$\mu$ pair and an up (charm) quark of 0.13 $\times$ 10$^{-6}$ (1.31 $\times$ 10$^{-6}$), 0.07 $\times$ 10$^{-6}$ (0.89 $\times$ 10$^{-6}$), and 0.25 $\times$ 10$^{-6}$ (2.59 $\times$ 10$^{-6}$) for vector, scalar, and tensor CLFV interactions, respectively.