Measurement of CP violation in $B^0\to \psi(\to\ell^+\ell^-)K^0_\mathrm{S}(\to \pi^+\pi^-)decays$

Abstract

A measurement of time-dependent $C\!P$ violation in the decays of $B^0$ and $\overline{B}^0$ mesons to the final states ${J\!/\!\psi(\to\mu^+\mu^-)K^0_\mathrm{S}}$, $\psi(2S)(\to\mu^+\mu^-)K^0_\mathrm{S}$ and $J\!/\!\psi(\to e^+e^-)K^0_\mathrm{S}$ with $K^0_\mathrm{S}\pi^+\pi^-$ is presented. The data correspond to an integrated luminosity of $6\,\mathrm{fb}^{-1}$ collected at a centre-of-mass energy of $\sqrt{s}=13\,\mathrm{TeV}$ with the LHCb detector. The $C\!P$-violation parameters are measured to be \begin{align*} S_{\psi K^0_\mathrm{S}} &= 0.717 \pm 0.013\,(\text{stat}) \pm 0.008\,(\text{syst}), \\ C_{\psi K^0_\mathrm{S}} &= 0.008 \pm 0.012\,(\text{stat}) \pm 0.003\,(\text{syst}). \end{align*} This measurement of $S_{\psi K^0_\mathrm{S}}$ represents the most precise single measurement of the CKM angle $\beta$ to date and is more precise than the current world average. In addition, measurements of the $C\!P$-violation parameters of the individual channels are reported and a combination with the LHCb Run 1 measurements is performed.A measurement of time-dependent CP violation in the decays of $B^0$ and $\overline{B}^0$ mesons to the final states $J/\psi(\to\mu^+\mu^-)K^0_S$, $\psi(2S)(\to\mu^+\mu^-)K^0_S$ and $J/\psi(\to e^+e^-)K^0_S$ with $K^0_S\to\pi^+\pi^-$ is presented. The data correspond to an integrated luminosity of 6 fb${}^{-1}$ collected at a centre-of-mass energy of $\sqrt{s}=13$ TeV with the LHCb detector. The CP-violation parameters are measured to be \begin{align*} S_{\psi K^0_S} &= 0.717 \pm 0.013 (\text{stat}) \pm 0.008 (\text{syst}), \\ C_{\psi K^0_S} &= 0.008 \pm 0.012 (\text{stat}) \pm 0.003 (\text{syst}). \end{align*} This measurement of $S_{\psi K^0_S}$ represents the most precise single measurement of the CKM angle $\beta$ to date and is more precise than the current world average. In addition, measurements of the CP-violation parameters of the individual channels are reported and a combination with the LHCb Run 1 measurements is performed