Searching for exotic Higgs bosons from top quark decays at the HL-LHC

TL;DR

This paper investigates the potential to discover exotic spin-0 Higgs-like particles with unusual couplings to top quarks at the HL-LHC, using machine learning to analyze rare top decays.

Contribution

It introduces a model-independent approach focusing on top-involving Yukawa couplings and employs advanced machine learning techniques for collider analysis.

Findings

Significant signal significance for exotic states lighter than the top quark.

Enhanced detection prospects during the high luminosity phase of the LHC.

Complementary to previous studies focusing on light quark couplings.

Abstract

Exotic spin-$0$ states with unusual couplings with the gauge and matter fields of the Standard Model are worth exploring at the CERN LHC. Though our approach is largely model independent, we take inspiration from flavor models based on some discrete symmetries which predict a set of a scalar and a pseudoscalar having purely off-diagonal Yukawa interactions with quarks and leptons. In a previous paper, some of us explored how to decipher such exotic scalar and pseudoscalar states whose off-diagonal Yukawa couplings involve light quarks. In this work we follow a complementary path and focus on the Yukawa couplings that necessarily involve a top quark. If one such spin-$0$ state is lighter than the top quark, then the rare decay of the latter, on account of the high yield of the $t\bar t$ events, could provide a potential hunting ground of those exotic states particularly during the high luminosity phase of the LHC run. We carry out an exhaustive collider analysis of some promising signatures of those exotic states using sophisticated Machine Learning techniques and obtain considerable signal significance.