Study of $CP$-Violating Asymmetries in ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ Decays

Study of $C P$ -Violating Asymmetries in $B^{0} \to π^{+} π^{-}$ Decays

K. Abe et al. (Belle Collaboration)

Phys. Rev. Lett. 89, 071801 – Published 26 July 2002

Abstract

We present a measurement of $C P$ -violating asymmetries in $B^{0} \to π^{+} π^{-}$ decays based on a $41.8 {f b}^{- 1}$ data sample collected at the $Υ (4 S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+} e^{-}$ collider. We fully reconstruct one neutral $B$ meson as a $B^{0} \to π^{+} π^{-}$ $C P$ eigenstate and identify the flavor of the accompanying $B$ meson from its decay products. From the asymmetry in the distribution of the time intervals between the two $B$ meson decay points, we obtain the $C P$ -violating asymmetry parameters $S_{π π} = - {1.21}_{- 0.27}^{+ 0.38} (s t a t)_{- 0.13}^{+ 0.16} (s y s t)$ and $A_{π π} = + {0.94}_{- 0.31}^{+ 0.25} (s t a t) \pm 0.09 (s y s t)$ .