Search for CP violation in $${{{\textrm{D}}}^{{0}}} \rightarrow {{\textrm{K}} _{\text {S}}^{{0}}} {{\textrm{K}} _{\text {S}}^{{0}}} $$ D 0 → K S 0 K S 0 decays in proton–proton collisions at $$\sqrt{s} = 13\,\text {Te}\hspace{-.08em}\text {V} $$ s = 13 Te V

Abstract

Abstract A search is reported for charge-parity $$CP$$ CP violation in $${{{\textrm{D}}}^{{0}}} \rightarrow {{\textrm{K}} _{\text {S}}^{{0}}} {{\textrm{K}} _{\text {S}}^{{0}}} $$ D 0 → K S 0 K S 0 decays, using data collected in proton–proton collisions at $$\sqrt{s} = 13\,\text {Te}\hspace{-.08em}\text {V} $$ s = 13 Te V recorded by the CMS experiment in 2018. The analysis uses a dedicated data set that corresponds to an integrated luminosity of 41.6 $$\,\text {fb}^{-1}$$ 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 $${{{\textrm{D}}}^{{*+}}} \rightarrow {{{\textrm{D}}}^{{0}}} {{{\mathrm{\uppi }}}^{{+}}} $$ D ∗ + → D 0 π + and $${{{\textrm{D}}}^{{*-}}} \rightarrow {\overline{{\textrm{D}}}^{{0}}} {{{\mathrm{\uppi }}}^{{-}}} $$ D ∗ - → D ¯ 0 π - . The $$CP$$ CP asymmetry in $${{{\textrm{D}}}^{{0}}} \rightarrow {{\textrm{K}} _{\text {S}}^{{0}}} {{\textrm{K}} _{\text {S}}^{{0}}} $$ D 0 → K S 0 K S 0 is measured to be $$A_{CP} ({{\textrm{K}} _{\text {S}}^{{0}}} {{\textrm{K}} _{\text {S}}^{{0}}} ) = (6.2 \pm 3.0 \pm 0.2 \pm 0.8)\%$$ A CP ( K S 0 K S 0 ) = ( 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 $$CP$$ CP asymmetry in the $${{{\textrm{D}}}^{{0}}} \rightarrow {{\textrm{K}} _{\text {S}}^{{0}}} {{{\mathrm{\uppi }}}^{{+}}} {{{\mathrm{\uppi }}}^{{-}}} $$ D 0 → K S 0 π + π - decay. This is the first $$CP$$ CP asymmetry measurement by CMS in the charm sector as well as the first to utilize a fully hadronic final state.