Searching for millicharges with the milliQan experiment

by Steven Lowette (Vrije Universiteit Brussel)

Tuesday Nov 18, 2025, 1:00 PM → 2:00 PM Europe/Brussels

E/3rd floor-E.349 - Seminar room (E.349) (Marc de Hemptinne (chemin du Cyclotron, 2, Louvain-la-Neuve))

The milliQan experiment is designed to search for particles carrying a small fraction of the elementary electric charge — so-called millicharged particles (mCPs) — using a modular detector located near the CMS experiment at the CERN Large Hadron Collider (LHC). Such particles arise naturally in a variety of extensions to the Standard Model, including theories with hidden sectors and dark photons, and could play a role in explaining the nature of dark matter. The milliQan detector consists of arrays of scintillator bars and slabs read out by high-gain photomultiplier tubes, optimized to detect the faint ionization signals produced by mCPs with charges as small as 10^−3 e. After a successful prototype run (“milliQan demonstrator”), a full-scale detector was installed and has been collecting data during Run 3 of the LHC. In this talk, I will introduce the motivation for millicharged particle searches, describe the design and performance of the milliQan detector, and present recent results and prospects for upcoming runs. milliQan’s sensitivity to a previously unexplored region of charge–mass parameter space provides a unique window into hidden sectors and complements the global search program for new physics at the intensity and energy frontiers.