Collisions in CMS produce gazillions of particles, but most of these (except muons) are readily absorbed by the heavy material of the CMS detector. One of the hypotheses for new physics beyond the particles that we know could be the presence of particles with a small electric charge, which would easily fly out of the detector. A few years ago, a new small detector was proposed to capture such particles, to be placed in an unused gallery above the CMS experiment. In 2019, VUB joined in on this experiment, and at this very moment we are finalizing construction of a first version of this detector that will take data during the LHC Run3 years 2023-2025.

A sketch of the detector and its positions with respect to CMS can be seen below. Unfortunately, it is not possible to visit the detector itself, but we will pass by the platform in the main CMS construction hall where the milliQan detector was constructed and tested before it was brought downstairs.

More info in a news item from Oct '22: https://cms.cern/news/milliqan-getting-ready-have-look-dark