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  • Open Access

Fermion-portal dark matter at a high-energy muon collider

Pouya Asadi1,*, Samuel Homiller2,†, Aria Radick1,‡, and Tien-Tien Yu1,§

  • 1Institute for Fundamental Science and Department of Physics, University of Oregon, Eugene, Oregon 97403, USA
  • 2Laboratory for Elementary Particle Physics, Cornell University, Ithaca, New York 14853, USA

  • *Contact author: pasadi@uoregon.edu
  • †Contact author: shomiller@cornell.edu
  • ‡Contact author: aradick@uoregon.edu
  • §Contact author: tientien@uoregon.edu
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Phys. Rev. D 112, 055038 – Published 26 September, 2025

DOI: https://doi.org/10.1103/p7p8-wqqb

Abstract

In this work, we provide a comprehensive study of fermion-portal dark matter models in the freeze-in regime at a future muon collider. For different possible nonsinglet fermion portals, we calculate the upper bound on the mediator’s mass arising from the relic abundance calculation and discuss the reach of a future muon collider in probing their viable parameter space in prompt and long-lived particle search strategies. In particular, we develop rudimentary search strategies in the prompt region and show that cuts on the invariant dilepton or dijet masses, the missing transverse mass MT2, pseudorapidity and energy of leptons or jets, and the opening angle between the lepton or the jet pair can be employed to subtract the Standard Model background. In the long-lived particle regime, we discuss the signals of each model and calculate their event counts. In this region, the lepton-(quark-)portal model signal consists of charged tracks (R-hadrons) that either decay in the detector to give rise to a displaced lepton (jet) signature, or are detector stable and give rise to heavy stable charged track signals. As a byproduct, a pipeline is developed for including the nontrivial parton distribution function of a muon component inside a muon beam; it is shown that this leads to nontrivial effects on the kinematic distributions and attainable significances. We also highlight phenomenological features of all models unique to a muon collider and hope our results, for this motivated and broad class of dark matter models, inform the design of a future muon collider detector. We also speculate on suggestions for improving the sensitivity of a muon collider detector to long-lived particle signals in fermion-portal models.

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Phys. Rev. D 112, 055038– Published 26 September, 2025
  • Received 12 March 2025
  • Accepted 8 August 2025
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