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

Abstract

We report measurements of time dependent decay rates for $B^0\to D^{(\ast )-}{\pi }^{+}$ decays and extraction of CP violation parameters that depend on ${\varphi }_3$. Using fully reconstructed $D^{(\ast )}\pi$ events and partially reconstructed $D^{\ast }\pi$ events from a data sample that contains 386 million $B\bar{B}$ pairs that was collected near the ${\rm Y}(4S)$ resonance, with the Belle detector at the KEKB asymmetric energy $e^{+}{e}^{-}$ collider, we obtain the CP violation parameters $S^{+}(D^{(\ast )}\pi )$ and $S^{-}(D^{(\ast )}\pi )$. We obtain $S^{+}(D^{\ast }\pi )=0.049\pm 0.020(\mathrm{stat})\pm 0.011(\mathrm{sys})$, $S^{-}(D^{\ast }\pi )=0.031\pm 0.019(\mathrm{stat})\pm 0.011(\mathrm{sys})$, and $S^{+}(D\pi )=0.031\pm 0.030(\mathrm{stat})\pm 0.012(\mathrm{sys})$, $S^{-}(D\pi )=0.068\pm 0.029(\mathrm{stat})\pm 0.012(\mathrm{sys})$. These results are an indication of CP violation in $B^0\to D^{\ast -}{\pi }^{+}$ and $B^0\to D^{-}{\pi }^{+}$ decays at the $2.5\sigma$ and $2.2\sigma$ levels, respectively. If we use the values of $R_{D^{(\ast )}\pi }$ that are derived using assumptions of factorization and SU(3) symmetry, the branching fraction measurements for the $D_s^{(\ast )}\pi$ modes, and lattice QCD calculations, we can restrict the allowed region of $|\sin (2{\varphi }_1+{\varphi }_3)|$ to be above 0.44 and 0.52 at 68% confidence level from the $D^{\ast }\pi$ and $D\pi$ modes, respectively.

14 pages, 12 figures, submitted to Physical Review D

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