The LHC as a TeV Muon Beam Dump: Muonphilic Scalars at FASER

TL;DR

This paper proposes using the LHC's intense forward muon flux to search for muonphilic scalars, leveraging FASER's upgraded detector to explore new physics regions, including the muon g-2 anomaly.

Contribution

It introduces a novel method to produce and detect muonphilic scalars using LHC muons, expanding FASER's physics reach beyond background suppression.

Findings

FASER and FASER2 can probe new parameter space for muonphilic scalars.

The method can potentially explain the muon g-2 anomaly.

Upgraded FASER detector enhances background discrimination.

Abstract

The FASER experiment was designed to study long-lived dark sector particles and neutrinos traveling in the forward direction at the LHC. Neutrinos are predominantly produced from meson decays, which also result in an intense energetic flux of muons in the forward direction regularly observed by FASER. So far, these muons are treated only as backgrounds to neutrino and new physics studies, and extensive effort is required to suppress them. In this study, we consider the opposite scenario and use muons produced in the forward direction to produce new muonphilic scalars, which can then be searched for at the FASER detector. To minimize the backgrounds for this search, we make use of an upgraded preshower component, which is expected to be installed at FASER before the end of Run 3, and is capable of spatially resolving two energetic photons. We find that FASER, and its upgrade, FASER2 can probe currently unconstrained regions of parameter space, including regions that can potentially explain the $(g-2)_{\mu}$ anomaly. This highlights the physics opportunities that the intense TeV muon beam at the LHC can bring.