Shedding light on the electroweak phase transition from exotic Higgs boson decays at the lifetime frontiers

TL;DR

This paper investigates how long-lived particles from exotic Higgs decays can be used to probe the electroweak phase transition at the HL-LHC, revealing regions inaccessible to prompt decay searches.

Contribution

It introduces a novel approach using LLP searches at specific detectors to explore the electroweak phase transition involving a light singlet scalar.

Findings

LLP searches can significantly extend the parameter space probed for EWPT.

Certain scenarios show LLP detection is more effective than prompt decay searches.

The study demonstrates the potential of FASER, MAPP, and CMS-Timing detectors in this context.

Abstract

We study the scenarios where a strongly first-order electroweak phase transition (EWPT) is triggered by a light singlet scalar, which has feeble interactions to the Higgs. Since the singlet scalar is light and has weak couplings, it can decay at a macroscopic distance away from the collision point. Therefore, it can be regarded as a long-lived particles (LLP) in such scenarios. We perform the searches of the LLPs from the exotic Higgs decays, at the FASER, MAPP and CMS-Timing detectors of the 14 TeV HL-LHC, to probe the strongly first-order EWPT. In certain scenarios, we show that the LLP searches can help to reach the parameter space of the strongly first-order EWPT remarkably, where the searches for promptly exotic Higgs decays are not valid.