Observation of $ τ^- \rightarrow π^- ν_τ e^+ e^-$ and search for $τ^- \rightarrow π^- ν_τ μ^+ μ^-$
Creators: name: Belle Collaboration
name: Jin, Y.
name: Aihara, H.
name: Epifanov, D.
name: Adachi, I.
name: Said, S. Al
name: Asner, D. M.
name: Aulchenko, V.
name: Aushev, T.
name: Ayad, R.
name: Babu, V.
name: Badhrees, I.
name: Bahinipati, S.
name: Bansal, V.
name: Behera, P.
name: Berger, M.
name: Bhardwaj, V.
name: Bilka, T.
name: Biswal, J.
name: Bobrov, A.
name: Bonvicini, G.
name: Bozek, A.
name: Bračko, M.
name: Campajola, M.
name: Cao, L.
name: Červenkov, D.
name: Chekelian, V.
name: Chen, A.
name: Cheon, B. G.
name: Chilikin, K.
name: Cho, H. E.
name: Cho, K.
name: Choi, Y.
name: Choudhury, S.
name: Cinabro, D.
name: Cunliffe, S.
name: Di Carlo, S.
name: Doležal, Z.
name: Dong, T. V.
name: Dossett, D.
name: Eidelman, S.
name: Fast, J. E.
name: Ferber, T.
name: Fulsom, B. G.
name: Garg, R.
name: Gaur, V.
name: Gabyshev, N.
name: Giri, A.
name: Goldenzweig, P.
name: Golob, B.
name: Greenwald, D.
name: Grzymkowska, O.
name: Haba, J.
name: Hayasaka, K.
name: Hayashii, H.
name: Hedges, M. T.
name: Hou, W. -S.
name: Huang, K.
name: Iijima, T.
name: Inami, K.
name: Inguglia, G.
name: Ishikawa, A.
name: Iwasaki, M.
name: Iwasaki, Y.
name: Jacobs, W. W.
name: Jeon, H. B.
name: Jia, S.
name: Joffe, D.
name: Joo, K. K.
name: Kahn, J.
name: Kaliyar, A. B.
name: Karyan, G.
name: Kawasaki, T.
name: Kichimi, H.
name: Kiesling, C.
name: Kim, D. Y.
name: Kim, H. J.
name: Kim, K. T.
name: Kim, S. H.
name: Kinoshita, K.
name: Kodyš, P.
name: Korpar, S.
name: Kotchetkov, D.
name: Križan, P.
name: Kroeger, R.
name: Krokovny, P.
name: Kulasiri, R.
name: Kumar, R.
name: Kuzmin, A.
name: Kwon, Y. -J.
name: Lalwani, K.
name: Lange, J. S.
name: Lee, J. Y.
name: Lee, S. C.
name: Li, C. H.
name: Li, L. K.
name: Li, Y. B.
name: Gioi, L. Li
name: Libby, J.
name: Lieret, K.
name: Liptak, Z.
name: Liventsev, D.
name: Lu, P. -C.
name: Luo, T.
name: MacNaughton, J.
name: Masuda, M.
name: Matsuda, T.
name: Matvienko, D.
name: Merola, M.
name: Miyabayashi, K.
name: Miyata, H.
name: Mizuk, R.
name: Mori, T.
name: Mussa, R.
name: Nakano, E.
name: Nakao, M.
name: Nath, K. J.
name: Natkaniec, Z.
name: Nayak, M.
name: Niiyama, M.
name: Nisar, N. K.
name: Nishida, S.
name: Ogawa, S.
name: Ono, H.
name: Onuki, Y.
name: Pakhlov, P.
name: Pakhlova, G.
name: Pal, B.
name: Pardi, S.
name: Park, H.
name: Park, S. -H.
name: Patra, S.
name: Paul, S.
name: Pedlar, T. K.
name: Pestotnik, R.
name: Piilonen, L. E.
name: Popov, V.
name: Prencipe, E.
name: Rostomyan, A.
name: Russo, G.
name: Sahoo, D.
name: Sakai, Y.
name: Salehi, M.
name: Sandilya, S.
name: Santelj, L.
name: Sanuki, T.
name: Savinov, V.
name: Schneider, O.
name: Schnell, G.
name: Schueler, J.
name: Schwanda, C.
name: Seino, Y.
name: Senyo, K.
name: Seon, O.
name: Sevior, M. E.
name: Shebalin, V.
name: Shen, C. P.
name: Shiu, J. -G.
name: Shwartz, B.
name: Simon, F.
name: Singh, J. B.
name: Sokolov, A.
name: Solovieva, E.
name: Stanič, S.
name: Starič, M.
name: Stottler, Z. S.
name: Strube, J. F.
name: Sumiyoshi, T.
name: Takizawa, M.
name: Tamponi, U.
name: Tanida, K.
name: Tenchini, F.
name: Trabelsi, K.
name: Uchida, M.
name: Uglov, T.
name: Unno, Y.
name: Uno, S.
name: Urquijo, P.
name: Usov, Y.
name: Van Tonder, R.
name: Varner, G.
name: Vinokurova, A.
name: Vorobyev, V.
name: Vossen, A.
name: Wang, B.
name: Wang, C. H.
name: Wang, M. -Z.
name: Wang, P.
name: Watanuki, S.
name: Won, E.
name: Yang, S. B.
name: Ye, H.
name: Yin, J. H.
name: Yuan, C. Z.
name: Yusa, Y.
name: Zhang, Z. P.
name: Zhilich, V.
name: Zhukova, V.
Publisher: name: arXiv
Year: 2019
Subjects: subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present the first measurements of branching fractions of rare tau-lepton decays, $τ^- \rightarrow π^- ν_τ \ell^+ \ell^-$ ($\ell = e$ or $μ$), using a data sample corresponding to 562 fb$^{-1}$ collected at a center-of-mass energy of 10.58 GeV with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The $τ^- \rightarrow π^- ν_τe^+ e^-$ decay is observed for the first time with 7.0$σ$ significance. The partial branching fraction determined by the structure-dependent mechanisms mediated by either a vector or an axial-vector current for the mass region $M_{πe e}&gt;1.05$ GeV/$c^2$ is measured to be $\mathcal{B}(τ^-\rightarrow π^- ν_τe^+ e^-)[M_{π^- e^+ e^-}&gt;1.05~{\rm GeV}/c^2] = (5.90 \pm 0.53 \pm 0.85 \pm 0.11) \times 10^{-6}$, where the first uncertainty is statistical, the second is systematic, and the third is due to the model dependence. In the full phase space, due to the different detection efficiencies for the structure-dependent mechanisms mediated by axial-vector and vector currents, the branching fraction varies from $\mathcal{B}_{A}(τ^-\rightarrow π^- ν_τe^+ e^-) = (1.46 \pm 0.13 \pm 0.21) \times 10^{-5}$ to $\mathcal{B}_{V}(τ^-\rightarrow π^- ν_τe^+ e^-) = (3.01 \pm 0.27 \pm 0.43) \times 10^{-5}$, respectively. An upper limit is set on the branching fraction of the $τ^- \rightarrow π^- ν_τμ^+ μ^-$ decay, $\mathcal{B}(τ^-\rightarrow π^- ν_τμ^+ μ^-) &lt; 1.14 \times 10^{-5}$, at the 90% confidence level.
description: 8 pages, 5 figures, accepted by PRD(RC)