Topportunities at the LHC: Rare Top Decays with Light Singlets

TL;DR

This paper explores the potential of the High Luminosity LHC to detect rare top quark decays involving light singlet particles, which could reveal new physics beyond the Standard Model through exotic decay channels and long-lived particle signatures.

Contribution

It introduces the study of rare top decays mediated by higher-dimensional operators in SMEFT extended with light singlets of various spins, highlighting their detectability at the HL-LHC.

Findings

Many exotic top decay channels could be observed at the HL-LHC.

Light singlets may produce distinctive long-lived particle signals.

SM decay of the partner top provides a natural trigger for searches.

Abstract

The discovery of the top quark, the most massive elementary particle yet known, has given us a distinct window into investigating the physics of the Standard Model and Beyond. With a plethora of top quarks to be produced in the High Luminosity era of the LHC, the exploration of its rare decays holds great promise in revealing potential new physics phenomena. We consider higher-dimensional operators contributing to top decays in the SMEFT and its extension by a light singlet species of spin 0, 1/2, or 1, and exhibit that the HL-LHC may observe many exotic top decays in a variety of channels. Light singlets which primarily talk to the SM through such a top interaction may also lead to distinctive long-lived particle signals. Searching for such long-lived particles in top-quark decays has the additional advantage that the SM decay of the other top quark in the same event provides a natural trigger.