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新山 雅之 所属 京都産業大学 理学部 物理科学科 職種 教授 |
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| 発行・発表の年月 | 2019/04 |
| 形態種別 | その他 |
| 査読 | 査読あり |
| 標題 | Measurement of $\mathcal{R}(D)$ and $\mathcal{R}(D^{\ast})$ with a semileptonic tagging method |
| 執筆形態 | その他 |
| 著者・共著者 | The Belle Collaboration,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,P. Behera,M. Belhorn,K. Belous,M. Berger,F. U. Bernlochner,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,N. Braun,F |
| 概要 | We report a measurement of the ratios of branching fractions $\mathcal{R}(D)
= {\cal B}(\bar{B} \to D \tau^- \bar{\nu}_{\tau})/{\cal B}(\bar{B} \to D \ell^- \bar{\nu}_{\ell})$ and $\mathcal{R}(D^{\ast}) = {\cal B}(\bar{B} \to D^* \tau^- \bar{\nu}_{\tau})/{\cal B}(\bar{B} \to D^* \ell^- \bar{\nu}_{\ell})$, where $\ell$ denotes an electron or a muon. The results are based on a data sample containing $772\times10^6$ $B\bar{B}$ events recorded at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. The analysis utilizes a method where the tag-side $B$ meson is reconstructed in a semileptonic decay mode, and the signal-side $\tau$ is reconstructed in a purely leptonic decay. The measured values are $\mathcal{R}(D)= 0.307 \pm 0.037 \pm 0.016$ and $\mathcal{R}(D^{\ast})= 0.283 \pm 0.018 \pm 0.014$, where the first uncertainties are statistical and the second are systematic. These results are in agreement with the Standard Model predictions within $0.2$ and $1.1$ standard deviations, respectively, while their combination agrees with the Standard Model predictions within $1.2$ standard deviations. |