3 years ago

# Measurement of the Decays $\boldsymbol{B\to\eta\ell\nu_\ell}$ and $\boldsymbol{B\to\eta^\prime\ell\nu_\ell}$ in Fully Reconstructed Events at Belle.

K. Inami, G. Karyan, D. Joffe, J. Dingfelder, P. Križan, V. Babu, Y. J. Kim, I. Badhrees, Y. Iwasaki, B. Bhuyan, S. Eidelman, H. Hayashii, K. H. Kang, Y. Choi, K. K. Joo, A. Bobrov, H. B. Jeon, R. Chistov, Z. Doležal, S. Korpar, D. Y. Kim, N. Dash, D. M. Asner, A. Ishikawa, D. Kotchetkov, M. Bračko, S. Al Said, W.-S. Hou, R. Ayad, A. Garmash, A. Chen, P. Behera, H. Aihara, C. Beleño, T. Ferber, S. Di Carlo, A. M. Bakich, Belle Collaboration, D. Červenkov, Y. Jin, T. E. Browder, J. Biswal, B. G. Fulsom, H. Farhat, V. Gaur, K. Kinoshita, A. Frey, J. B. Kim, T. Iijima, P. Kodyš, K. T. Kim, P. Urquijo, M. T. Hedges, R. Gillard, J. E. Fast, D. Cinabro, T. Hara, R. Itoh, S.-K. Choi, B. G. Cheon, T. Aushev, P. Goldenzweig, V. Bansal, M. J. Kim, N. Gabyshev, G. Inguglia

We report branching fraction measurements of the decays $B^+\to\eta\ell^+\nu_\ell$ and $B^+\to\eta^\prime\ell^+\nu_\ell$ based on 711~fb$^{-1}$ of data collected near the $\Upsilon(4S)$ resonance with the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider. This data sample contains 772 million $B\bar B$~events. One of the two $B$~mesons is fully reconstructed in a hadronic decay mode. Among the remaining ("signal-$B$") daughters, we search for the $\eta$~meson in two decay channels, $\eta\to\gamma\gamma$ and $\eta\to\pi^+\pi^-\pi^0$, and reconstruct the $\eta^{\prime}$~meson in $\eta^\prime\to\eta\pi^+\pi^-$ with subsequent decay of the $\eta$ into $\gamma\gamma$. Combining the two $\eta$ modes and using an extended maximum likelihood, the $B^+\to\eta\ell^+\nu_\ell$ branching fraction is measured to be $(4.2\pm 1.1 (\rm stat.)\pm 0.3 (\rm syst.))\times 10^{-5}$. For $B^+\to\eta^\prime\ell^+\nu_\ell$, we observe no significant signal and set an upper limit of $0.72\times 10^{-4}$ at 90\% confidence level.

Publisher URL: http://arxiv.org/abs/1703.10216

DOI: arXiv:1703.10216v3

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