Optimal use of timing measurement in vertex reconstruction at CMS

¹ INFN Trieste (Italy)
² University of Trieste (Italy)
³ PSI Villigen (Switzerland)
⁴ INFN Milano Bicocca (Italy)
⁵ University of Rome La Sapienza, INFN Roma1 (Italy)

^* e-mail: ksenia.de.leo@cern.ch

Published online: 7 October 2025

Abstract

The MIP Timing Detector (MTD) is a novel component of the CMS experiment, currently under construction as part of the upgrade program to prepare for the High Luminosity era of the LHC (HL-LHC). The MTD will provide precise time information for charged particles and will play an important role in the mitigation of the high pileup expected in HL-LHC. The timing will be used to disentangle vertices that cannot be distinguished spatially, thus reducing the vertex cross-contamination and the effects of pileup on the physics observables used for any data analysis. This contribution presents the recent developments in the vertex reconstruction with the use of timing, which feature a reduction in the vertex CPU-time by 30% with respect to the previous algorithm without loss in performance. Moreover, it introduces a new set of tools useful to evaluate the behaviour of different reconstruction algorithms in terms of time resolution, number of reconstructed vertices and pileup rejection, which can serve as a benchmark for future developments in the field.