Search for CP violation in D 0 → K S 0 K S 0 decays in proton-proton collisions at s = 13 Te V

Abstract

A search is reported for charge-parity $\mathrm{CP}$ violation in ${\text{D}}^0\to {\text{K}}_{\text{S}}^0{\text{K}}_{\text{S}}^0$ decays, using data collected in proton-proton collisions at $\sqrt{s}=13\text{Te}\text{V}$ recorded by the CMS experiment in 2018. The analysis uses a dedicated data set that corresponds to an integrated luminosity of 41.6 ${\text{fb}}^{-1}$ , 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 $\text{D}_{}^{\ast +}\to {\text{D}}^0{\pi }^{+}$ and $\text{D}_{}^{\ast -}\to {\overline{\text{D}}}^0{\pi }^{-}$ . The $\mathrm{CP}$ asymmetry in ${\text{D}}^0\to {\text{K}}_{\text{S}}^0{\text{K}}_{\text{S}}^0$ is measured to be $A_{\mathrm{CP}}\left({\text{K}}_{\text{S}}^0{\text{K}}_{\text{S}}^0\right)=(6.2\pm 3.0\pm 0.2\pm 0.8)\%$ , where the three uncertainties represent the statistical uncertainty, the systematic uncertainty, and the uncertainty in the measurement of the $\mathrm{CP}$ asymmetry in the ${\text{D}}^0\to {\text{K}}_{\text{S}}^0{\pi }^{+}{\pi }^{-}$ decay. This is the first $\mathrm{CP}$ asymmetry measurement by CMS in the charm sector as well as the first to utilize a fully hadronic final state.