Precision Timing with LYSO:Ce Crystals and SiPM Sensors in the CMS MTD Barrel Timing Layer

The CMS detector at the CERN Large Hadron Collider is undergoing an extensive Phase II upgrade program to prepare for the challenging conditions of the High-Luminosity LHC. A new timing detector in CMS will measure minimum ionizing particles (MIPs) with a time resolution of 30-40 ps for MIP signals at a rate of 2.5 Mhit/s per channel at the beginning of HL-LHC operation. The precision time information from this detector will be used to reduce the effects of the high levels of pileup expected at the HL-LHC, bringing new capabilities to the CMS detector. The central barrel part of the detector, Barrel Timing Layer (BTL), will be based on LYSO:Ce crystals read out with SiPMs with TOFHIR ASICs for the front-end readout. The BTL will use elongated crystal bars, read out by a SiPM on each end of the crystal, in order to maximize detector performance within the constraints of space, cost, and channel count. This geometry enables to cover large surfaces with a minimal active area of the photodetectors, thus reducing noise and power consumption. The conceptual design of BTL have been validated with measurements with test beam of high energy particles. The close to final prototypes of the detector modules and readout electronics have been produced and are being tested.