Observation of $CP$ violation in $B^{0}\!\to{J\mskip-3mu/\mskip-2mu\psi}\rho(770)^0$ decays

TL;DR

This paper reports the first observation of time-dependent CP violation in B0 meson decays to charmonium states, using LHCb data at 13 TeV, with results more precise than previous measurements and implications for understanding CP-violating phases.

Contribution

It provides the first measurement of time-dependent CP violation in B0 to J/psi rho(770)^0 decays and improves the precision of related CP-violation parameters using LHCb data.

Findings

First observation of CP violation in this decay mode

Measurement of CP-violation parameters with improved precision

Stringent constraints on the CP-violating phase in B_s decays.

Abstract

The time-dependent $CP$ asymmetry in $B^{0}\!\to{J\mskip-3mu/\mskip-2mu\psi}\rho(770)^0$ decays is measured using proton-proton collision data corresponding to an integrated luminosity of $6\,\text{fb}^{-1}$, collected with the LHCb detector at a center-of-mass energy of $13\,\text{TeV}$ during the years 2015-2018. The $CP$-violation parameters for this process are determined to be $2\beta^{\rm eff}_{c\bar{c}d} = 0.710 \pm 0.084 \pm 0.028\,\text{rad}$ and $|\lambda| = 1.019 \pm 0.034 \pm 0.009$, where the first uncertainty is statistical and the second systematic. This constitutes the first observation of time-dependent $CP$ violation in $B$ meson decays to charmonium final states mediated by a $b\!\to{c\bar{c}d}$ transition. These results are consistent with, and two times more precise than, the previous LHCb measurement based on a data sample collected at 7 and $8\,\text{TeV}$ corresponding to an integrated luminosity of $3\,\text{fb}^{-1}$. Assuming approximate SU(3) flavor symmetry, these two measurements are combined to set the most stringent constraint on the enguin contribution, $\Delta\phi_{s}$, to the $CP$-violating phase $\phi_{s}$ in $B^{0}_{s}\!\to{J\mskip-3mu/\mskip-2mu\psi}\phi(1020)$ decays, yielding $\Delta\phi_{s} = 5.0 \pm 4.2\,\text{mrad}$.