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arXiv · 1612.00529

Measurement of the $τ$ lepton polarization and $R(D^*)$ in the decay $\bar{B} \to D^* τ^- \barν_τ$

S. Hirose·T. Iijima·I. Adachi·K. Adamczyk·H. Aihara·S. Al Said·D. M. Asner·H. Atmacan·V. Aulchenko·T. Aushev·R. Ayad·V. Babu·I. Badhrees·A. M. Bakich·V. Bansal·E. Barberio·P. Behera·M. Berger·B. Bhuyan·J. Biswal·A. Bondar·G. Bonvicini·A. Bozek·M. Bračko·T. E. Browder·D. Červenkov·P. Chang·A. Chen·B. G. Cheon·K. Chilikin·R. Chistov·K. Cho·Y. Choi·D. Cinabro·M. Danilov·N. Dash·S. Di Carlo·J. Dingfelder·Z. Doležal·Z. Drásal·D. Dutta·S. Eidelman·D. Epifanov·H. Farhat·J. E. Fast·T. Ferber·B. G. Fulsom·V. Gaur·N. Gabyshev·A. Garmash·P. Goldenzweig·B. Golob·D. Greenwald·J. Grygier·J. Haba·K. Hara·J. Hasenbusch·K. Hayasaka·H. Hayashii·T. Higuchi·W. -S. Hou·C. -L. Hsu·K. Inami·G. Inguglia·A. Ishikawa·R. Itoh·Y. Iwasaki·W. W. Jacobs·I. Jaegle·Y. Jin·D. Joffe·K. K. Joo·T. Julius·Y. Kato·T. Kawasaki·H. Kichimi·C. Kiesling·D. Y. Kim·J. B. Kim·K. T. Kim·M. J. Kim·S. H. Kim·K. Kinoshita·P. Kodyš·S. Korpar·D. Kotchetkov·P. Križan·P. Krokovny·T. Kuhr·R. Kulasiri·R. Kumar·Y. -J. Kwon·J. S. Lange·C. H. Li·L. Li·Y. Li·L. Li Gioi·J. Libby·D. Liventsev·M. Lubej
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Abstract

We report the first measurement of the $τ$ lepton polarization $P_τ(D^*)$ in the decay $\bar{B} \rightarrow D^* τ^- \barν_τ$ as well as a new measurement of the ratio of the branching fractions $R(D^{*}) = \mathcal{B}(\bar {B} \rightarrow D^* τ^- \barν_τ) / \mathcal{B}(\bar{B} \rightarrow D^* \ell^- \barν_\ell)$, where $\ell^-$ denotes an electron or a muon, and the $τ$ is reconstructed in the modes $τ^- \rightarrow π^- ν_τ$ and $τ^- \rightarrow ρ^- ν_τ$. We use the full data sample of $772 \times 10^6$ $B{\bar B}$ pairs recorded with the Belle detector at the KEKB electron-positron collider. Our results, $P_τ(D^*) = -0.38 \pm 0.51 {\rm (stat.)} ^{+0.21}_{-0.16} {\rm (syst.)}$ and $R(D^*) = 0.270 \pm 0.035{\rm (stat.)} ^{+0.028}_{-0.025}{\rm (syst.)}$, are consistent with the theoretical predictions of the Standard Model.

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S. Hirose, T. Iijima, I. Adachi, K. Adamczyk, H. Aihara, S. Al Said, D. M. Asner, H. Atmacan, V. Aulchenko, T. Aushev, R. Ayad, V. Babu, I. Badhrees, A. M. Bakich, V. Bansal, E. Barberio, P. Behera, M. Berger, B. Bhuyan, J. Biswal, A. Bondar, G. Bonvicini, A. Bozek, M. Bračko, T. E. Browder, D. Červenkov, P. Chang, A. Chen, B. G. Cheon, K. Chilikin, R. Chistov, K. Cho, Y. Choi, D. Cinabro, M. Danilov, N. Dash, S. Di Carlo, J. Dingfelder, Z. Doležal, Z. Drásal, D. Dutta, S. Eidelman, D. Epifanov, H. Farhat, J. E. Fast, T. Ferber, B. G. Fulsom, V. Gaur, N. Gabyshev, A. Garmash, P. Goldenzweig, B. Golob, D. Greenwald, J. Grygier, J. Haba, K. Hara, J. Hasenbusch, K. Hayasaka, H. Hayashii, T. Higuchi, W. -S. Hou, C. -L. Hsu, K. Inami, G. Inguglia, A. Ishikawa, R. Itoh, Y. Iwasaki, W. W. Jacobs, I. Jaegle, Y. Jin, D. Joffe, K. K. Joo, T. Julius, Y. Kato, T. Kawasaki, H. Kichimi, C. Kiesling, D. Y. Kim, J. B. Kim, K. T. Kim, M. J. Kim, S. H. Kim, K. Kinoshita, P. Kodyš, S. Korpar, D. Kotchetkov, P. Križan, P. Krokovny, T. Kuhr, R. Kulasiri, R. Kumar, Y. -J. Kwon, J. S. Lange, C. H. Li, L. Li, Y. Li, L. Li Gioi, J. Libby, D. Liventsev, M. Lubej. 2017-05-03. Measurement of the $τ$ lepton polarization and $R(D^*)$ in the decay $\bar{B} \to D^* τ^- \barν_τ$. https://doi.org/10.1103/physrevlett.118.211801

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