Precision timing with low gain avalanche detectors in the CMS MTD Endcap Timing Layer

Abstract

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, precision timing can offset the performance degradation due to event pileup at the HL-LHC, recovering the purity of vertices of current LHC conditions. As such, a new timing layer will be introduced to measure minimum ionizing particles (MIPs) with a time resolution of 30 ps. The endcap region of this MIP Timing Detector (MTD) will be instrumented with a hermetic double layer of silicon low gain avalanche detectors (LGADs), covering the high radiation pseudo-rapidity region between |η|=1.6 to 3.0. Radiation tolerance studies of the LGADs indicate excellent performances adequate to cope with the Endcap Timing Layer (ETL) requirements. The LGADs have intrinsic gain, which enhances the MIP signal and provides adequate signal-to-noise for good timing precision. We present the status of the art for the LGADs for the endcap region of the MTD and report on recent beam test results.