Search for CP violation in D⁰→K_S⁰K_S⁰ decays in proton–proton collisions at √s=13TeV

A search is reported for charge-parity CP violation in D0→KS0KS0 decays, using data collected in proton–proton collisions at s=13TeV recorded by the CMS experiment in 2018. The analysis uses a dedicated data set that corresponds to an integrated luminosity of 41.6fb-1, which consists of about 10 billion events containing a pair of b hadrons, nearly all of which decay to charm hadrons. The flavor of the neutral D meson is determined by the pion charge in the reconstructed decays D∗+→D0π+ and D∗-→D¯0π-. The CP asymmetry in D0→KS0KS0 is measured to be ACP(KS0KS0)=(6.2±3.0±0.2±0.8)%, where the three uncertainties represent the statistical uncertainty, the systematic uncertainty, and the uncertainty in the measurement of the CP asymmetry in the D0→KS0π+π- decay. This is the first CP asymmetry measurement by CMS in the charm sector as well as the first to utilize a fully hadronic final state.