The golden modesB0→J/ψKS,Lin the era of precision flavor physics

Abstract

$CP$ violation is a major challenge of contemporary particle physics. It has been discovered in kaon decays and appears also in $B$ decays, where the ${B}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}_{\mathrm{S},\mathrm{L}}$ channels are considered to be clean probes of this phenomenon. Recent $B$-factory data challenge the description of $CP$ violation in the standard model of particle physics, showing some ``tension'' with theoretical predictions. We take a detailed look at certain standard-model contributions, which are usually neglected, and point out that they can be included unambiguously through measurements of the ${B}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{0}$ observables. Using the most recent data, we show that the tension with the standard model is softened, and we constrain a possible new-physics phase in ${B}^{0}\ensuremath{-}{\overline{B}}^{0}$ mixing. Our strategy is crucial to fully exploit the accuracy of the search for this kind of new physics at the LHC and future super-flavor factories.