# Light scalar production from Higgs bosons and FASER 2

## TL;DR

This paper investigates how the FASER 2 experiment can detect light scalar particles produced via Higgs decays, expanding the potential to explore new physics beyond current limits through modifications in experimental design.

## Contribution

It provides a detailed analysis of FASER 2's sensitivity to Higgs portal scalars and suggests design modifications to enhance discovery potential.

## Key findings

- FASER 2 can significantly extend the search for Higgs portal scalars.
- Modest design changes can increase the explored parameter space by orders of magnitude.
- Current limits allow up to 10% of Higgs bosons to decay into new scalars.

## Abstract

The most general renormalizable interaction between the Higgs sector and a new gauge-singlet scalar $S$ is governed by two interaction terms: cubic and quartic. The quartic interaction is only loosely constrained by invisible Higgs decays. Given current experimental limits about $10\%$ of all Higgs bosons created at the LHC can be converted to new scalars with the mass up to $m_{\rm Higgs}/2$. This can significantly extend the reach of the LHC-based Intensity Frontier experiments. We analyze the sensitivity of the FASER experiment to this model and discuss modest changes in the FASER 2 design that would allow to explore an orders-of-magnitude wider part of the Higgs portal's parameter space.