Measurements of CP Violation in $B^0 \to D^{*-}π^+$ and $B^0 \to D^- π^+$ Decays

Abstract

We report measurements of time dependent decay rates for $B^0 \to D^{(*)-}π^+$ decays and extraction of CP violation parameters that depend on $ϕ_3$. Using fully reconstructed $D^{(*)}π$ events and partially reconstructed $D^{*}π$ events from a data sample that contains 386 million $B\bar{B}$ pairs that was collected near the $Υ(4S)$ resonance, with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider, we obtain the CP violation parameters $S^+ (D^{(*)}π)$ and $S^- (D^{(*)}π)$. We obtain $S^+ (D^* π) = 0.049 \pm 0.020(\mathrm{stat}) \pm 0.011(\mathrm{sys})$, $S^- (D^* π) = 0.031 \pm 0.019(\mathrm{stat}) \pm 0.011(\mathrm{sys})$, and $S^+ (D π) = 0.031 \pm 0.030(\mathrm{stat}) \pm 0.012(\mathrm{sys})$, $S^- (D π) = 0.068 \pm 0.029(\mathrm{stat}) \pm 0.012(\mathrm{sys})$. These results are an indication of CP violation in $B^0 \to D^{*-}π^+$ and $B^0 \to D^- π^+$ decays at the $2.5 σ$ and $2.2 σ$ levels, respectively. If we use the values of $R_{D^{(*)}π}$ that are derived using assumptions of factorization and SU(3) symmetry, the branching fraction measurements for the $D_s^{(*)} π$ modes, and lattice QCD calculations, we can restrict the allowed region of $|\sin (2ϕ_1 + ϕ_3)|$ to be above 0.44 and 0.52 at 68% confidence level from the $D^* π$ and $D π$ modes, respectively.