Exploring muonphilic dark matter with the $Z_2$-even mediator at muon colliders

TL;DR

This paper investigates the potential of a future 3 TeV muon collider to detect muonphilic dark matter models that could explain the Galactic Center GeV Excess, using various search strategies and detailed analysis.

Contribution

It provides a comprehensive study of discovery prospects for muonphilic dark matter at a muon collider, focusing on simplified models with a Z2-even mediator and multiple search channels.

Findings

Projected exclusion limits cover a large part of the viable parameter space.

Muon collider can decisively test muonphilic dark matter explanations for the GCE.

Multiple search strategies enhance discovery potential.

Abstract

The Galactic Center GeV Excess (GCE) remains a compelling but enigmatic signal from the inner region of our galaxy. Muonphilic dark matter (DM), which couples exclusively to muons via a new mediator, provides a viable explanation for the GCE and relic density while naturally evading constraints from direct detection, collider searches and other multi-messenger observations. Based on the viable non-resonant parameter space identified in previous global fits, we perform a comprehensive study exploring the prospects for discovering such muonphilic DM in the context of a future $3$ TeV muon collider, focusing on simplified models with a $Z_2$-even mediator. Four distinct search strategies are investigated: visible on-shell mediator decays ($\mu^{+}\mu^{-}\gamma$ final state), invisible on-shell mediator decays (mono-photon plus missing energy), mono-photon production via off-shell mediators, and vector boson fusion production.Through a detailed signal-background analysis using cut-and-count methods, we project the exclusion limits at $95\%$ confidence level for seven representative models across a wide range of mediator masses. Our results demonstrate that the projected limits cover a significant portion of the viable parameter space that explains the GCE, establishing a muon collider as a decisive machine for testing the muonphilic DM hypothesis.