B0 decays reconstruction in the channel JPsi K0s at the CMS experiment

In the collisions between LHC beams a great number of particles is producted, and among them B0 mesons, that can decay in different final states. B0 decay in the channel JPsi K0_short is interesting because its final state is an eighenstate with defined CP. JPsi decays in two muons, while K0s in two pions: the former decay is instantaneus, the latter has a mean life of about 1 ns; the extrapolation of the tracks of the 4 particles gives as results two decay vertces: one is referred to B0 and JPsi, the other to the K0s. This work consists in the production of an utility able to reconstructed the quoted decay, that can be implemented in the CMS Offline Reconstruction Software. Reconstruction procedure has been tested over a simulated data sample (which highlighted a recostruction efficiency equal to 75%), and then it has been used to study LHC data from later 2016 (corresponding to an integrated luminosity of 8.503 fb^-1); these ones were selected by a group of filters, implemented in the software. Histograms of physical dimensions such as mass, transverse momentum and flight distance have been plotted as results of the analysis.