arXiv · 1608.06391
Measurement of the $τ$ lepton polarization in the decay ${\bar B} \rightarrow D^* τ^- {\bar ν_τ}$
Abstract
We report the first measurement of the $τ$ lepton polarization 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, with the decays $τ^- \rightarrow π^- ν_τ$ and $τ^- \rightarrow ρ^- ν_τ$. We use the full data sample of $772 \times 10^6$ $B{\bar B}$ pairs accumulated with the Belle detector at the KEKB electron-positron collider. Our preliminary results, $R(D^*) = 0.276 \pm 0.034{\rm (stat.)} ^{+0.029} _{-0.026}{\rm (syst.)}$ and $P_τ = -0.44 \pm 0.47 {\rm (stat.)} ^{+0.20} _{-0.17} {\rm (syst.)}$, are consistent with the theoretical predictions of the Standard Model within $0.6$ standard deviation.
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A. Abdesselam, I. Adachi, K. Adamczyk, H. Aihara, S. Al Said, K. Arinstein, Y. Arita, D. M. Asner, T. Aso, H. Atmacan, V. Aulchenko, T. Aushev, R. Ayad, T. Aziz, V. Babu, I. Badhrees, S. Bahinipati, A. M. Bakich, A. Bala, Y. Ban, V. Bansal, E. Barberio, M. Barrett, W. Bartel, A. Bay, I. Bedny, P. Behera, M. Belhorn, K. Belous, M. Berger, D. Besson, V. Bhardwaj, B. Bhuyan, J. Biswal, T. Bloomfield, S. Blyth, A. Bobrov, A. Bondar, G. Bonvicini, C. Bookwalter, C. Boulahouache, A. Bozek, M. Bračko, F. Breibeck, J. Brodzicka, T. E. Browder, E. Waheed, D. Červenkov, M. -C. Chang, P. Chang, Y. Chao, V. Chekelian, A. Chen, K. -F. Chen, P. Chen, B. G. Cheon, K. Chilikin, R. Chistov, K. Cho, V. Chobanova, S. -K. Choi, Y. Choi, D. Cinabro, J. Crnkovic, J. Dalseno, M. Danilov, N. Dash, S. Di Carlo, J. Dingfelder, Z. Doležal, D. Dossett, Z. Drásal, A. Drutskoy, S. Dubey, D. Dutta, K. Dutta, S. Eidelman, D. Epifanov, S. Esen, H. Farhat, J. E. Fast, M. Feindt, T. Ferber, A. Frey, O. Frost, B. G. Fulsom, V. Gaur, N. Gabyshev, S. Ganguly, A. Garmash, D. Getzkow, R. Gillard, F. Giordano, R. Glattauer, Y. M. Goh, P. Goldenzweig, B. Golob, D. Greenwald, M. Grosse Perdekamp, J. Grygier. 2016-08-23. Measurement of the $τ$ lepton polarization in the decay ${\bar B} \rightarrow D^* τ^- {\bar ν_τ}$. https://arxiv.org/abs/1608.06391
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