New BRIL subsystems illuminate CMS’s path through Run 3

After many months of meticulous preparations, new BRIL subsystems were installed in mid-January. The intervention will ensure that CMS can continue to achieve world leading accuracy in its measurement of luminosity and beam conditions for the remainder of Run 3.

The Beam Radiation, Instrumentation, and Luminosity (BRIL) group is responsible for the operation of three instruments dedicated to the measurement of luminosity and beam conditions: the Beam Condition Monitor “Fast” (BCM1F), the Beam Condition Monitor for Losses (BCM1L), and the Pixel Luminosity Telescope (PLT). Both PLT and BCM1F are based on silicon sensor technology, while BCM1L uses poly-crystalline diamond sensors. All three subsystems are supported by a carbon fibre structure which positions them ~1.8 m away from the interaction point.

During Run 2 (2015 to 2018), CMS was equipped with earlier versions of each system, which yielded valuable operational experience. The analysis of the performance of each detector as it aged from radiation damage informed the rebuild plans in anticipation of the current Run, Run 3. Thus, in addition to the BRIL detectors installed just before the start of Run 3 in 2021, the preparation during Long Shutdown 2 - the period of time between Run 2 and 3 - included the pre-production of a second copy of the BRIL systems to be installed in the middle of Run 3.

Given the spectacular performance of the LHC during 2024, it became clear that several of the BRIL systems would reach end-of-life by the end of the year due to the accumulated radiation damage. Thus, production efforts for each subsystem were ramped up to full speed in order to meet the goal of installing these new BRIL systems in early 2025. The CMS Technical Coordination team had to juggle a very complex sequence during the 2024-2025 year-end technical stop, where the installation of CO₂-related infrastructure meant that only one side of CMS could be made accessible for the installation.

Despite a challenging integration process, which included many gruelling thermal cycles to stress-test all components, the BRIL team was able to complete the process by mid-December. In keeping with the tradition of baptizing each BRIL module after pizza-related names 🍕, we are pleased to introduce “Hawaii” and “Calzone” and eagerly anticipate the first beams of 2025!

Further Links:

Photos of CMS BRIL -Z PLT/BCM1F/BCM1L Transport and Installation

Photos of CMS BRIL -Z PLT/BCM1F/BCM1L Integration