Ricerc@Sapienza

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 starting in 2026. In particular, a new timing detector, the MTD, will measure minimum ionizing particles with a time resolution of 30-50 ps. The precision time information from the MTD will reduce the effects of the high levels of pile-up expected at HL-LHC and will bring new and unique capabilities to the CMS detector; it will allow the use of 4D reconstruction algorithms and will further discriminate interaction vertices within the same bunch crossing to recover the track purity of vertices in current LHC conditions.

The technology selected for the central part of the detector, the Barrel Timing Layer, consists of scintillating crystals of Lutetium Yttrium Orthosilicate doped with Cerium (LYSO:Ce) read out with Silicon PhotoMultipliers.

The first part of this project is aiming at characterize LYSO:Ce scintillating crystals from different vendors by measuring and comparing geometrical and optical properties of crystal bar samples. This activity will be performed at the Segrè laboratory in Sapienza. In addition a subset of the crystals will be irradiated with photons in Enea - Calliope facility to check the radiation tolerance by testing the optical properties before and after the irradiation.

In the second part of the project an optical bench dedicated to the test of the crystal arrays, coupled with SiPM arrays with final packaging and electronics, will be built. A pre-production of O(100) arrays from two or three selected vendors will be tested with the new bench to investigate more deeply the homogeneity in the properties of the crystals and the reliability of the final producer. Finally this project will be crucial in the identification of the vendor for the full detector production and the tuning of the procedure for the Quality Control of the crystals during the final production.