Search for millicharged particles at the LHC with the milliQan prototype

We report on the results of a recent search for fractionally charged particlesusing a data sample of 37.5 $\textrm{fb}^{-1}$ proton-proton collisions at $\sqrt{s} = 13$ TeVprovided by the CERN Large Hadron Collider in 2018. This search was carried out with a prototype scintillator-based detector, which allows the first sensitivity to particles with charges $\le0.1$e at a hadron collider. The existence of new particles with masses between 20 and 4700 MeV is excluded at 95\% confidence level for charges between 0.006e and 0.3e, depending on their mass. New sensitivity is achieved for masses larger than 700 MeV. The successful operation of the milliQan prototype provides crucial lessons for the design of the full milliQan detector.