Observation of ${\tau }^{–}\to {\pi }^{–}{\nu }_{\tau }{e}^{+}{e}^{–}$ and search for ${\tau }^{–}\to {\pi }^{–}{\nu }_{\tau }{\mu }^{+}{\mu }^{–}$

Journal Article · 15 October 2019 · Physical Review. D.

DOI: https://doi.org/10.1103/PhysRevD.100.071101 · OSTI ID:1570499

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

We present the first measurements of branching fractions of rare tau-lepton decays, τ^– → π^–ν_τℓ⁺ℓ^– (ℓ = 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^– → π^–ν_τe⁺e^– decay is observed for the first time with 7.0σ 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_πee > 1.05 GeV/c² is measured to be B(τ^– → π^–ν_τe⁺e^–)[M_{π^–e⁺e^–} > 1.05 GeV/c²] = (5.90 ± 0.53 ± 0.85 ± 0.11) × 10^–6, where the first uncertainty is statistical, the second is systematic, and the third is due to 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 B_A(τ^– → π^–ν_τe⁺e^–) = (1.46 ± 0.13 ± 0.21) × 10^–5 to B_V(τ^– → π^–ν_τe⁺e^–) = (3.01 ± 0.27 ± 0.43) × 10^–5, respectively. An upper limit is set on the branching fraction of the τ^– → π^–ν_τμ⁺μ^– decay, B(τ^– → π^–ν_τμ⁺μ^–) < 1.14 × 10^–5, at the 90% confidence level.

• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
• Grant/Contract Number: SC0012704
• OSTI ID: 1570499
• Journal Information: Physical Review. D., Journal Name: Physical Review. D. Journal Issue: 7 Vol. 100; ISSN PRVDAQ; ISSN 2470-0010
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English