Development of the CMS MIP timing detector

The CMS detector at the CERN Large Hadron Collider is undergoing an extensive Phase II upgrade programme to prepare for the challenging conditions of the High-Luminosity LHC. In particular, a new timing detector, the MTD, will measure minimum ionizing particles with a time resolution of 30–50 ps and hermetic coverage up to a pseudo-rapidity of |η|=3 . The MTD will consist of a central barrel region based on L(Y)SO:Ce crystals read out with SiPMs and two end-caps instrumented with radiation-tolerant low gain avalanche detectors. The precision time information from the MTD will reduce the effects of the high levels of pile-up expected at the High-Luminosity LHC and will bring new and unique capabilities to the CMS detector. The time information assigned to each track will enable 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. We present the motivations for precision timing at the High-Luminosity LHC, the overall detector design and technological choices including ongoing R&D; studies targeting enhanced timing performance and radiation tolerance.