Study of $B\to D^{**}l\nu$ with full reconstruction tagging

We report a study of semileptonic $B$ decays to $P$-wave $D^{**}$ mesons. Semileptonic decay to a $D_2^{*}$ meson is observed for the first time and its product branching ratio is measured to be $\mathcal{B}(B^{+}\to {\overline{D}}_2^{*0}{\ell }^{+}\nu )\times \mathcal{B}({\overline{D}}_2^{*0}\to D^{-}{\pi }^{+})=0.22\pm 0.03(\mathrm{stat}.)\pm 0.04(\mathrm{syst}.)\%$. The result is obtained using fully reconstructed $B$ tags from a data sample that contains $657\times {10}^{6}B\overline{B}$ pairs collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

Figure 1

$M_{\nu }^2$ spectra before (1) and after (2) background subtraction for: (a) $B^{+}\to D^{-}{\pi }^{+}{\ell }^{+}\nu$, (b) $B^{+}\to D^{*-}{\pi }^{+}{\ell }^{+}\nu$, (c) $B^0\to {\overline{D}}^0{\pi }^{-}{\ell }^{+}\nu$, (d) $B^0\to {\overline{D}}^{*0}{\pi }^{-}{\ell }^{+}\nu$. The curves are the fits, which are described in the text.

Figure 2

Hadronic invariant mass distributions for: (a) $B^{+}\to D^{-}{\pi }^{+}{\ell }^{+}\nu$, (b) $B^{+}\to D^{*-}{\pi }^{+}{\ell }^{+}\nu$, (c) $B^0\to {\overline{D}}^0{\pi }^{-}{\ell }^{+}\nu$, (d) $B^0\to {\overline{D}}^{*0}{\pi }^{-}{\ell }^{+}\nu$. Insets show the distributions before background subtraction in the region around the narrow $D^{**}$’s. The background is shown as the hatched histogram. The curves are the fits, which are described in the text.

Figure 3

Helicity distributions for (a) $D_0^{*}$, (b) $D_v^{*}$, (c) $D_2^{*}$. The curves represent the fits, described in the text.

Figure 4

$w$ distributions for (a) $D_0^{*}$, (b) $D_v^{*}$, (c) $D_2^{*}$. The curves are the fits, which are described in the text.