Detectors at HL-LHC will face an unprecedented level of event
pile-ups. CMS has decided to instrument a charged-particle timing
layer aiming at the reduction of pile-up effects via precision
time-tagging. In this contribution, I will first review the design
choices for the CMS timing layer, crystal+SiPM in the barrel region
and ultra-fast silicon detectors in the endcap, and then explain the
improvements that this new detector brings to the physics reach of
CMS
Viviana Cavaliere