Evidence for $CP$ Violation in ${B}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{0}$ Decays

Evidence for $C P$ Violation in $B^{0} \to J / ψ π^{0}$ Decays

B. Aubert et al. (The BABAR Collaboration)

Phys. Rev. Lett. 101, 021801 – Published 10 July 2008

Abstract

We present measurements of the branching fraction and time-dependent $C P$ asymmetries in $B^{0} \to J / ψ π^{0}$ decays based on $466 \times 10^{6}$ $Υ (4 S) \to B \bar{B}$ events collected with the BABAR detector at the SLAC PEP-II asymmetric-energy $B$ factory. We measure the $C P$ asymmetry parameters $S = - 1.23 \pm 0.21 (stat) \pm 0.04 (syst)$ and $C = - 0.20 \pm 0.19 (stat) \pm 0.03 (syst)$ , where the measured value of ( $S$ , $C$ ) is 4.0 standard deviations from (0, 0) including systematic uncertainties. The branching fraction is determined to be $B (B^{0} \to J / ψ π^{0}) = [1.69 \pm 0.14 (stat) \pm 0.07 (syst)] \times 10^{- 5}$ .