Dark Higgs Bosons at FASER

TL;DR

FASER at the LHC can effectively search for dark Higgs bosons produced via meson decays, offering a promising and complementary method to existing experiments for discovering these light, weakly-coupled particles.

Contribution

This paper demonstrates FASER's potential to discover dark Higgs bosons, highlighting its sensitivity and complementarity to other experimental approaches.

Findings

FASER can detect dark Higgs bosons produced in meson decays.

FASER's sensitivity is comparable to larger proposed experiments.

Dark Higgs bosons can be discovered with small detector volumes.

Abstract

FASER, ForwArd Search ExpeRiment at the LHC, has been proposed as a small, very far forward detector to discover new, light, weakly-coupled particles. Previous work showed that with a total volume of just $\sim 0.1 - 1~\rm{m}^3$, FASER can discover dark photons in a large swath of currently unconstrained parameter space, extending the discovery reach of the LHC program. Here we explore FASER's discovery prospects for dark Higgs bosons. These scalar particles are an interesting foil for dark photons, as they probe a different renormalizable portal interaction and are produced dominantly through $B$ and $K$ meson decays, rather than pion decays, leading to less collimated signals. Nevertheless, we find that FASER is also a highly sensitive probe of dark Higgs bosons with significant discovery prospects that are comparable to, and complementary to, much larger proposed experiments.