Systematically Testing Singlet Models for $(g-2)_\mu$

TL;DR

This paper systematically analyzes Standard Model singlet particle models that could explain the muon g-2 anomaly, evaluating their testability across various current and future accelerator experiments, including muon colliders.

Contribution

It provides a comprehensive assessment of all viable singlet models for muon g-2 and identifies the experimental reach of different collider and fixed-target searches.

Findings

Nearly all viable singlet scenarios can be tested by existing and planned experiments.

Future muon colliders above the GeV scale are uniquely capable of testing these models up to the TeV unitarity limit.

GeV-scale singlets may be better probed by 100 GeV muon colliders than by TeV-scale colliders.

Abstract

We comprehensively study all viable new-physics scenarios that resolve the muon $(g-2)_\mu$ anomaly with only Standard Model singlet particles coupled to muons via renormalizable interactions. Since such models are only viable in the MeV -- TeV mass range and require sizable muon couplings, they predict abundant accelerator production through the same interaction that resolves the anomaly. We find that a combination of fixed-target (NA64$\mu$, $M^3$), $B$-factory (BABAR, Belle II), and collider (LHC, muon collider) searches can cover nearly all viable singlets scenarios, independently of their decay modes. In particular, future muon collider searches offer the only certain test of singlets above the GeV scale, covering all higher masses up to the TeV-scale unitarity limit for these models. Intriguingly, we find that $\mathcal{O}(100~\mathrm{GeV})$ muon colliders may yield better coverage for GeV-scale singlets compared to TeV-scale concepts, which has important implications for the starting center-of-mass energy of a staged muon collider program.