Simulation studies on precise timing information during High Luminosity LHC.

We present prospects for the usage of precise timing information during the high luminosity phase of the LHC (HL-LHC) at the CMS experiment. During the HL-LHC the instantaneous luminosity is estimated to be greater than 10$^{34}$ cm$^{-2}$s$^{-1}$, resulting in about 140 simultaneous proton-proton collisions (pileup) that occur every 25 nsec.\\ The time information can be exploited to improve the object reconstruction, for instance obtaining an alternative vertex determination, based on pure timing information, with a O(cm) resolution. This is particularly relevant in events with low track multiplicity (e.g. $H \rightarrow \gamma\gamma$), where the vertex cannot be precisely determined with tracking information. A time requirement can be also used to reduce the occupancy in the electromagnetic calorimeter (ECAL), removing the energy deposits with a time not compatible to the one expected from a particle coming from the hard collision. This may have important consequences in many aspects: reduction of event size, improvement of photon and jet energy resolution.