Observation of $CP$ violation in $B^0\to J/\ddot{I}ˆ\ddot{I}(770{)}^0$ decays

Abstract

The time-dependent $CP$ asymmetry in $B^0\to J/\ddot{I}ˆ\ddot{I}(770{)}^0$ 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 $2β^{\rm eff}_{c\bar{c}d} = 0.710 \pm 0.084 \pm 0.051\,\text{rad}$ and $|\hat{I}»|=1.019\pm 0.034\pm 0.024$, where the first uncertainty is statistical and the second systematic. This constitutes the first observation of time-dependent $CP$ violation in $B^0\to J/\ddot{I}ˆ\ddot{I}(770{)}^0$ 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, $\hat{I}”\ddot{I}{•}_s$, to the $CP$-violating phase $\ddot{I}{•}_s$ in $B_s^0\to J/\ddot{I}ˆ\ddot{I}•(1020)$ decays, yielding $\hat{I}”\ddot{I}{•}_s=5.0\pm 4.6\text{mrad}$.

All 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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