Charmless semileptonic B decays at Belle

Abstract

We report two analyses involving semileptonic $B$ meson decays to charmless final states: ${B^{+}\to \eta^{(\prime)}\ell^{+}\nu_{\ell} }$ and ${ B^{0}\to \pi^{-}\tau^{+}\nu_{\tau} }$. These results are based on a 711 fb$^{-1}$ data sample, corresponding to $772 \times 10^{6}$ $B\bar{B}$ pairs, collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^{+}e^{-}$ collider. One of the two $B$ mesons is fully reconstructed into hadronic decay modes, whereas the remainder of the event is used to study the signal channel. Branching ratios are extracted using a binned maximum likelihood fit method, resulting in $ {\cal B}(B^{+}\to \eta\ell^{+}\nu_{\ell}) = (0.42\pm0.11_{\rm stat}\pm 0.03_{\rm syst} )\times 10^{-4} $. However, given the low significance for the other channels, an upper limit at 90\% confidence level is provided: ${ {\cal B}(B^{+}\to \eta^{\prime}\ell^{+}\nu_{\ell}) < 0.76 \times 10^{-4} }$ and ${ {\cal B}(B^{0}\to \pi^{-}\tau^{+}\nu_{\tau}) < 2.5 \times 10^{-4} }$.

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