Quality control of LYSO:Ce crystals for the CMS barrel MIP timing detector

In the next years, the Large Hadron Collider will enter its High-Luminosity (HL-LHC) phase. Many CMS subsystems will be upgraded to maintain the current physics performance, despite the higher levels of pileup and radiation. To further mitigate the pileup, a MIP Timing Detector (MTD) for charged particles will be constructed, with a target time resolution of 30- 60 ps, to distinguish the primary vertices of tracks using timing information. The detector will be positioned between the tracker and the electromagnetic calorimeter. The MTD is divided into two regions, the Barrel and the Endcap Timing Layers (BTL/ETL). The active elements of BTL are arrays of lutetium-yttrium-oxyorthosilicate (LYSO) scintillating bars doped with cerium (LYSO:Ce), each readout by two silicon photo-multipliers (SiPM) arrays. The quality of BTL LYSO crystals in the production phase is controlled in a dedicated laboratory in INFN-Rome1. This is done, both for a sample of arrays and single crystals, by monitoring dimensional properties, light output, time resolution, optical cross-talk and decay time, by means of a Na-22 radioactive source.