Searching for Muonphilic Dark Sectors with Proton Beams

TL;DR

This paper explores the potential of proton beam-dump experiments to detect muon-specific dark sector particles, providing sensitivity projections that could reveal new physics related to the muon anomalous magnetic moment.

Contribution

It introduces a simplified-model framework for muon-coupled light scalars and evaluates the sensitivity of NA62 and SHiP experiments to these exotics in the sub-GeV mass range.

Findings

Significant yield of muonphilic scalars in sub-GeV range.

Projections competitive with muon-beam experiments.

Accesses new parameter space relevant to the (g-2)_μ anomaly.

Abstract

Proton beam-dump experiments are a high-intensity source of secondary muons and provide an opportunity to probe muon-specific dark sectors. We adopt a simplified-models framework for an exotic light scalar particle coupling predominantly or exclusively to muons. Equipped with state-of-the-art muon simulations, we compute the sensitivity reach in the parameter space $(m_S, \, g_\mu)$ of the dark mediator, examining in detail the examples of the experiment NA62 in beam-dump mode and the proposed experiment SHiP. We find a significant yield of such exotics in the sub-GeV mass range. Our projections are competitive with those of primary muon-beam experiments and complementary to current constraints, spanning uncharted parameter space and accessing new physics potentially responsible for the $(g-2)_\mu$ anomaly.