Abstract |
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We report a preliminary measurement of $\cos2\beta$ in
$B^0\rightarrow D^{(*)0}h^0$ decays with a time-dependent Dalitz plot
analysis of $D^0\rightarrow K_S\pi^+\pi^-$, where $h^0$ is a light
neutral meson such as $\pi^0$, $\eta$, $\eta'$ or $\omega$. The strong
phase variation on the Dalitz plot allows the access to the angle
$\beta$ with only a two-fold ambiguity ($\beta+\pi$). Using $311\times
10^{6}$ $B\overline{B}$ pairs collected at the Babar detector, we obtain
$\cos2\beta = 0.54 \pm 0.54 \pm 0.08 \pm 0.18$,
$\sin2\beta = 0.45 \pm 0.36 \pm 0.05 \pm 0.07$, and
$|\lambda| = 0.975^{+0.093}_{-0.085} \pm 0.012 \pm 0.002 $,
where the first errors are statistical, the second are experimental
systematic uncertainties, and the third are the signal Dalitz model
uncertainties. This measurement favors the solution of $\beta=
22^\circ$ over $68^\circ$ at an $87\%$ confidence level.
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