We present a measurement of the ratio Rμ=Bτ−→μ−ν¯μντ/Bτ−→e−ν¯eντ 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, Rμ = 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.

Test of light-lepton universality in τ decays with the Belle II experiment / Adachi, I., Adamczyk, K., Aggarwal, L., Aihara, H., Akopov, N., Aloisio, A., Anh Ky, N., Asner, D.M., Atmacan, H., Aushev, V., Aversano, M., Ayad, R., Babu, V., Bae, H., Bahinipati, S., Bambade, P., Banerjee, S., Bansal, S., Barrett, M., Baudot, J., et al.. - In: JOURNAL OF HIGH ENERGY PHYSICS. - ISSN 1029-8479. - 2024:8(2024). [10.1007/JHEP08(2024)205]

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

Aloisio A.;Campajola M.;De Nardo G.;Di Capua F.;Gaudino G.;Giordano R.;Merola M.;Mirra M.;Pardi S.;Russo Guido;
2024

Abstract

We present a measurement of the ratio Rμ=Bτ−→μ−ν¯μντ/Bτ−→e−ν¯eντ 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, Rμ = 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.
2024
Test of light-lepton universality in τ decays with the Belle II experiment / Adachi, I., Adamczyk, K., Aggarwal, L., Aihara, H., Akopov, N., Aloisio, A., Anh Ky, N., Asner, D.M., Atmacan, H., Aushev, V., Aversano, M., Ayad, R., Babu, V., Bae, H., Bahinipati, S., Bambade, P., Banerjee, S., Bansal, S., Barrett, M., Baudot, J., et al.. - In: JOURNAL OF HIGH ENERGY PHYSICS. - ISSN 1029-8479. - 2024:8(2024). [10.1007/JHEP08(2024)205]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/985081
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