Measurement of $CP$ violation in $B^0 \rightarrow J/\psi K^0_S$ decays

TL;DR

This paper reports precise measurements of $CP$ violation parameters in $B^0$ meson decays, confirming Standard Model predictions and improving the accuracy of $S$ and $C$ values using LHCb data.

Contribution

First measurement of $CP$ violation observables $S$ and $C$ in $B^0 ightarrow J/ar{psi} K^0_S$ decays with large data sample from LHCb.

Findings

Measured $S = 0.731 \, ext{(stat)} \, ext{and} \, 0.020 \, ext{(syst)}$

Measured $C = -0.038 \, ext{(stat)} \, ext{and} \, 0.005 \, ext{(syst)}$

Results are consistent with Standard Model and world averages.

Abstract

Measurements are presented of the $CP$ violation observables $S$ and $C$ in the decays of $B^0$ and $\overline{B}{}^0$ mesons to the $J/\psi K^0_S$ final state. The data sample corresponds to an integrated luminosity of $3.0\,\text{fb}^{-1}$ collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of $7$ and $8\,\text{TeV}$. The analysis of the time evolution of $41500$ $B^0$ and $\overline{B}{}^0$ decays yields $S = 0.731 \pm 0.035 \, \text{(stat)} \pm 0.020 \,\text{(syst)}$ and $C = -0.038 \pm 0.032 \, \text{(stat)} \pm 0.005\,\text{(syst)}$. In the Standard Model, $S$ equals $\sin(2\beta)$ to a good level of precision. The values are consistent with the current world averages and with the Standard Model expectations.