Test of light-lepton universality in τ decays with the Belle II experiment

• Published in: The journal of high energy physics Vol. 2024; no. 8; pp. 205 - 22
• Main Authors: Adachi, I., Asner, D. M., Aushev, V., Babu, V., Bahinipati, S., Bambade, P., Bansal, S., Bennett, J. V., Bernlochner, F. U., Bierwirth, L., Bilka, T., Biswas, D., Bobrov, A., Borah, J., Bussino, S., Cheon, B. G., Chilikin, K., Corona, L., Das, S., De La Motte, S. A., Dey, S., Domínguez Jiménez, I., Ecker, P., Fillinger, T., Finck, C., Finocchiaro, G., Fodor, A., Fulsom, B. G., Ganiev, E., Grammatico, T., Greenwald, D., Gu, T., Guan, Y., Han, Y., Hayasaka, K., Hayashii, H., Heredia de la Cruz, I., Higuchi, T., Horak, P., Humair, T., Ji, Q. P., Jin, Y., Junkerkalefeld, H., Kawasaki, T., Kim, C.-H., Konno, T., Krokovny, P., Kuhr, T., Kumar, M., Lange, J. S., Liptak, Z., Liu, Q. Y., Liventsev, D., Maiti, R., Mancinelli, G., Manfredi, R., Marcantonio, D., Marinas, C., Martellini, C., Matvienko, D., Mehta, R., Meier, F., Metzner, F., Moneta, S., Mussa, R., Nakazawa, Y., Natochii, A., Nazaryan, G., Pakhlov, P., Pestotnik, R., Praz, C., Reiter, S., Rout, N., Sandilya, S., Santelj, L., Schmitt, C., Schwanda, C., Shtol, D., Simon, F., Skorupa, J., Sobie, R. J., Sokolov, A., Spataro, S., Stefkova, S., Stroili, R., Takahashi, M., Takizawa, M., Tenchini, F., Tittel, O., Torassa, E., Urquijo, P., Wang, M.-Z., Watanabe, M., Watanuki, S., Wessel, C., Won, E., Xu, X. P., Yin, J. H., Yoshihara, K., Zeng, F.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 26.08.2024; Springer Nature B.V; Springer; SpringerOpen
• Subjects: Classical and Quantum Gravitation; Collaboration; Couplings; e +-e − Experiments; Electrons; Elementary Particles; High Energy Physics - Experiment; Leptons; Luminosity; Muons; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Quantum Physics; Quarks; Regular Article - Experimental Physics; Relativity Theory; Sensors; Simulation; Software; Standard model (particle physics); String Theory; Tau Physics; -; Experiments; Tau Physics; electron, momentum spectrum; BELLE; universality; statistical; branching ratio; lepton; KEK-B; GeV; muon, coupling
• ISSN: 1029-8479; 1126-6708; 1029-8479
• DOI: 10.1007/JHEP08(2024)205

A bstract We present a measurement of the ratio R μ = B τ − → μ − ν ¯ μ ν τ / B τ − → e − ν ¯ e ν τ of branching fractions B of the τ lepton decaying to muons or electrons using data collected with the Belle II detector at the SuperKEKB e + e − collider. The sample has an integrated luminosity of 362 ± 2 fb − 1 at a centre-of-mass energy of 10.58 GeV. Using an optimised event selection, a binned maximum likelihood fit is performed using the momentum spectra of the electron and muon candidates. The result, R μ = 0.9675 ± 0.0007 ± 0.0036, where the first uncertainty is statistical and the second is systematic, is the most precise to date. It provides a stringent test of the light-lepton universality, translating to a ratio of the couplings of the muon and electron to the W boson in τ decays of 0.9974 ± 0.0019, in agreement with the standard model expectation of unity.