Study of channel B_s->J/Psi Phi at CMS

A study of the gold plated decay B_s->J/Psi Phi with the CMS experiment at LHC is presented. Thanks to the J/Psi->mu+mu- decay and the presence of three resonances overall, this channel is easily reconstructed. An angular analysis of the decay products allows to disentangle the different CP final states and to measure several mixing and CP-violation parameters. Special attention must be devoted to efficiently trigger on the two muons from the J/Psi.