Performance Tests of CMS Barrel Timing Layer Components for the MIP Timing Detector of the High Luminosity LHC

The Large Hadron Collider (LHC) and its experiments are preparing for major upgrades in preparation for the High-Luminosity LHC (HL-LHC) phase starting in 2029. The Compact Muon Solenoid (CMS) experiment will feature a precision timing layer called the Minimum Ionising Particle (MIP) Timing Detection Layer (MTD), comprising LYSO crystal bars with a 30-60 picosecond time resolution. Positioned just outside the tracker, the MTD aims to enhance particle reconstruction and vertex identification by mitigating the impact of up to 200 pileup events per crossing. It incorporates Thermoelectric coolers (TECs) attached to Silicon Photomultiplier (SiPM) modules, maintaining SiPM performance at -45º C and reducing dark current over the detector's run period. The TECs can be reverse biased for periodic annealing, optimizing SiPM functionality post radiation damage. Our project focused on assessing TEC performance at the CERN Tracker Integration Facility (TIF), confirming the achievement of the SiPM working point within TEC power limits. However, TEC efficiency in cooling cycles was slightly lower than expected, attributed to higher-than-anticipated TEC conductance opposing the thermoelectric effect. Further optimizations in thermal interfaces are planned to maximize TEC efficiency, ultimately expanding the operational margin of the BTL detector.