Ricerc@Sapienza

The Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) is undergoing an extensive Phase II upgrade program to prepare for the challenging conditions of the High-Luminosity LHC (HL-LHC). In particular, a new timing layer will measure minimum ionizing particles (MIPs) with a time resolution of ~30-50 ps. The precision time information from this detector will reduce the effects of the high pile-up expected at the HL-LHC and will bring new and unique capabilities to the CMS detector. It will allow 4D space-time event reconstruction to remove pile-up tracks inconsistent with the hard-interaction thus recovering the track purity of primary vertices in current LHC conditions. The new timing information will also provide novel identification capabilities for low energy charged particles and will open new possibilities in the search for long-lived particles predicted by theories beyond the standard model.

The technology selected for the central part of the detector, the Barrel Timing Layer (BTL), consists of scintillating crystal of Lutetium Yttrium Orthosilicate doped with Cerium (LYSO:Ce) arranged in arrays of small elongated bars read out by Silicon PhotoMultipliers (SiPMs).

This project will follow up on the research activity performed in 2019-2020 by the CMS Rome group which is responsible for the LYSO crystal characterization for the BTL. The project will focus on the definition and implementation of the procedure for the quality assurance and control tests of the crystals during the final production phase in 2021-2022. Novel measurements of light output, decay time and time resolution at -30 degrees and with a UV-light picosecond laser will be performed. The main activities will be carried out at the Segrè laboratory in Sapienza. In addition a subset of the crystals will be irradiated with photons in the Enea - Calliope facility to check the radiation tolerance by testing the crystal optical properties before and after the irradiation.