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Proposal for a dedicated search for millicharged and fractionally charged particles at LANL

Yu-Dai Tsai1,2,3,*, Insung Hwang4, Ryan Schmitz5, Matthew Citron6, Kranti Gunthoti1, Jacob Steenis6, Hoyong Jeong4, Hyunki Moon4, Jae Hyeok Yoo4 et al.

Ming Xiong Liu1

  • *Contact author: yt444@cornell.edu, yudaitsai@lanl.gov
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Phys. Rev. D 113, 015038 – Published 27 January, 2026

DOI: https://doi.org/10.1103/4bdh-sd5n

Abstract

In this paper, we propose an experiment, LANSCE-mQ, aiming to detect fractionally charged and millicharged particles (mCPs) using an 800 MeV proton beam fixed target at the Los Alamos Neutron Science Center (LANSCE) facility at Los Alamos National Laboratory. This search can shed new light on numerous fundamental questions, including charge quantization, the predictions of string theories and grand unification theories, the gauge symmetry of the Standard Model, dark sector models, and the tests of cosmic reheating. We propose to install two-layer scintillation detectors made of plastic (such as EJ-200) or CeBr3 to search for mCPs. Dedicated geant4 detector simulations and in situ measurements have been conducted to obtain a preliminary determination of the background rate. The dominant backgrounds are beam-induced neutrons and coincident dark current signals from the photomultiplier tubes, while beam-induced high-energy photons (γ’s) and cosmic muons are subdominant. We determined that LANSCE-mQ, the dedicated mCP experiment, has the leading mCP sensitivity for mass between ∼1 and 300 MeV.

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Phys. Rev. D 113, 015038– Published 27 January, 2026
  • Received 23 August 2024
  • Accepted 7 November 2025
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