Observation of $CP$ violation in $B^0\to J/\psi \rho (770{)}^0$ decays

Abstract

The time-dependent $CP$ asymmetry in $B^0\to J/\psi \rho (770{)}^0$ 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 $2{\beta }_{c\bar{c}d}^{\mathrm{eff}}=0.710\pm 0.084\pm 0.051\text{rad}$ and $|\lambda |=1.019\pm 0.034\pm 0.024$, where the first uncertainty is statistical and the second systematic. This constitutes the first observation of time-dependent $CP$ violation in $B^0\to J/\psi \rho (770{)}^0$ decays. Assuming approximate SU(3) flavor symmetry, these results are combined with the previous consistent LHCb measurement to set the most stringent constraint on the penguin contribution, $\Delta {\varphi }_s$, to the $CP$-violating phase ${\varphi }_s$ in $B_s^0\to J/\psi \varphi (1020)$ decays, yielding $\Delta {\varphi }_s=5.0\pm 4.6\text{mrad}$.

arXiv commentAll figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/1620/ (LHCb public pages)

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