Technical Proposal for the milliQan sub-detector

A dedicated detector, milliQan, is proposed for detecting new particles with small electric charge (down to $10^{-3}$ of the charge of the electron) produced by proton collisions at CERN's LHC Point 5. Such particles could be related to the dark matter in the Universe. The apparatus consists of two sub-detectors, each with four segmented layers of scintillating plastic optically coupled to high-gain photomultipliers, that will be installed before the end of LS2 in the existing PX56 drainage gallery above UXC. With the dataset that LHC Run3 will provide, milliQan will significantly extend the parameter space explored for new particles with small charges, and masses above 100 MeV.