Measurement of Time-Dependent $CP$ Asymmetries and Constraints on $\sin (2\beta +\gamma )$ with Partial Reconstruction of $B^0\to D^{*\mp }{\pi }^{\pm }$ Decays

We present a measurement of time-dependent $CP$-violating asymmetries in decays of neutral $B$ mesons to the final states $D^{*\mp }{\pi }^{\pm }$, using approximately $82\times {10}^6$ $B\overline{B}$ events recorded by the BABAR experiment at the PEP-II $e^{+}{e}^{-}$ storage ring. Events containing these decays are selected with a partial reconstruction technique, in which only the high-momentum ${\pi }^{\pm }$ from the $B$ decay and the low-momentum ${\pi }^{\mp }$ from the $D^{*\mp }$ decay are used. We measure the amplitude of the asymmetry to be $-0.063\pm 0.024(\mathrm{stat})\pm 0.014(\mathrm{syst})$ and compute bounds on $|\sin (2\beta +\gamma )|$.

Figure 1

The $m_{\mathrm{miss}}$ distributions for (a) lepton-tagged and (b) kaon-tagged events. The curves show, from bottom to top, the cumulative contributions of continuum, peaking $B\overline{B}$, combinatoric $B\overline{B}$, $B^0\to D^{*+}{\rho }^{-}$, and $B^0\to D^{*+}{\pi }^{-}$ events.

Figure 2

The asymmetry ${\mathcal{A}}_{CP}$ for (a) lepton-tagged and (b) kaon-tagged events. The curves show the projection of the PDF from the unbinned fit.

Figure 3

95% C.L. lower limit on $|\sin (2\beta +\gamma )|$ as a function of $r^{*}$. The solid curve corresponds to this analysis; the dashed curve includes the results of Ref. [12] for $B^0\to D^{*\mp }{\pi }^{\pm }$ only.