# Muon Beam Experiments to Probe the Dark Sector

## TL;DR

This paper proposes muon beam-dump experiments at CERN and Fermilab to search for new light scalar particles that could explain anomalies in muon physics, exploring unexplored parameter space.

## Contribution

It introduces a novel experimental approach using muon beam-dump techniques to detect light scalars with specific couplings, addressing current gaps in searches.

## Key findings

- Muon beam experiments can probe scalar masses below di-muon threshold.
- Both missing momentum and decay vertex searches are effective.
- Significant parameter space relevant to muon g-2 anomaly can be explored.

## Abstract

A persistence of several anomalies in muon physics, such as the muon anomalous magnetic moment and the muonic hydrogen Lamb shift, hints at new light particles beyond the Standard Model. We address a subset of these models that have a new light scalar state with sizable couplings to muons and suppressed couplings to electrons. A novel way to search for such particles would be through muon beam-dump experiments by (1) missing momentum searches; (2) searches for decays with displaced vertices. The muon beams available at CERN and Fermilab present attractive opportunities for exploring the new scalar with a mass below the di-muon threshold, and potentially covering a range of relevant candidate models. For the models considered in this paper, both types of signals, muon missing momentum and anomalous energy deposition at a distance, can probe a substantial fraction of the unexplored parameter space of the new light scalar, including a region that can explain the muon anomalous magnetic moment discrepancy.