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Probing Cosmic Ray Composition and Muonphilic Dark Matter via Muon Tomography

Cheng-en Liu, Rongfeng Zhang, Zijian Wang, Andrew Michael Levin, Leyun Gao, Jinning Li, Minxiao Fan, Youpeng Wu, Zibo Qin et al. (PKMu Collaboration)

Zibo Qin, Yong Ban, Zaihong Yang, Qite Li*, Chen Zhou†, and Qiang Li‡ (PKMu Collaboration)

  • State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China

  • *Contact author: liqt@pku.edu.cn
  • †Contact author: czhouphy@pku.edu.cn
  • ‡Contact author: qliphy0@pku.edu.cn
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Phys. Rev. Lett. 136, 151001 – Published 14 April, 2026

DOI: https://doi.org/10.1103/5jh7-fxf4

Abstract

This Letter presents a novel cosmic-ray scattering experiment employing a resistive plate chamber muon tomography system. By introducing the scattering angle between incident and outgoing cosmic-ray tracks as a key observable, this approach enables simultaneous studies of secondary cosmic-ray composition and searching for new physics. During a 63-day campaign, 1.18 million cosmic ray scattering events were recorded and analyzed. By performing combined template fits to the observed angular distribution, particle abundances are measured—for example, resolving the electron component at ∼2% precision. Furthermore, constraints are established on elastic muon–dark matter (DM) scattering cross sections for muonphilic dark matter. At the 95% confidence level, the limit reaches 1.61×10−17  cm2 for 1 GeV slow DM, demonstrating the sensitivity limit to light muon-coupled slow DM, in scenarios where a strongly interacting dark matter component is captured and thermalized within Earth, leading to large surface densities.

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Phys. Rev. Lett. 136, 151001– Published 14 April, 2026
  • Received 21 August 2025
  • Revised 27 November 2025
  • Accepted 27 February 2026
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