CMS-PAS-BPH-23-005

CMS-PAS-BPH-23-005
Search for $CP$ violation in $\mathrm{D}^0\to\mathrm{K}^0_{\mathrm{S}}\mathrm{K}^0_{\mathrm{S}}$ decay from proton-proton collisions at 13 TeV
CMS Collaboration
26 March 2024

Abstract: A search is reported for $CP$ violation in the $\mathrm{D}^0\to\mathrm{K}^0_{\mathrm{S}}\mathrm{K}^0_{\mathrm{S}}$ decay, using data collected from proton-proton collisions at $\sqrt{s} =$ 13 TeV recorded by the CMS experiment in 2018. A dedicated data set of about 10 billion events containing a pair of b hadrons, nearly all of which decay to charm hadrons, is used. The flavor of the neutral D meson is determined by the pion charge in the reconstructed decays $\mathrm{D}^{+}\to\mathrm{D}^0\pi^+$ and $\mathrm{D}^{-}\to\overline{\mathrm{D}}^0\pi^-$ . The $CP$ asymmetry in $\mathrm{D}^0\to\mathrm{K}^0_{\mathrm{S}}\mathrm{K}^0_{\mathrm{S}}$ is measured to be $A_{CP}(\mathrm{K}^0_{\mathrm{S}}\mathrm{K}^0_{\mathrm{S}}) =$ 6.2 $\pm$ 3.0 (stat) $\pm$ 0.2 (syst) $\pm$ 0.8 $(A_{CP}(\mathrm{K}^0_{\mathrm{S}}\pi^+\pi^-))$ %, where the last uncertainty is the $CP$ asymmetry in the $\mathrm{D}^0\to\mathrm{K}^0_{\mathrm{S}}\pi^+\pi^-$ decay. This result is consistent with no $CP$ violation within 2 standard deviations. This is the first measurement of $CP$ violation in the charm sector by the CMS experiment, and the first measurement of $CP$ asymmetry in the fully hadronic final state performed by CMS at the nominal LHC luminosity, using the new data parking technique.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to EPJC. The superseded preliminary plots can be found here.

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