We present a measurement of the ratio Rµ = B(τ − → µ− ν̄µ ντ )/B(τ − → e− ν̄e ντ ) 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.

Adachi, I., Adamczyk, K., Aggarwal, L., Aihara, H., Akopov, N., Aloisio, A., et al. (2024). Test of light-lepton universality in τ decays with the Belle II experiment. JOURNAL OF HIGH ENERGY PHYSICS, 2024(8) [10.1007/jhep08(2024)205].

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

Branchini, P.
Membro del Collaboration Group
;
Budano, A.
Membro del Collaboration Group
;
Bussino, S.
Membro del Collaboration Group
;
De Pietro, G.
Membro del Collaboration Group
;
Laurenza, M.
Membro del Collaboration Group
;
Martellini, C.
Membro del Collaboration Group
;
Martini, A.
Membro del Collaboration Group
;
2024-01-01

Abstract

We present a measurement of the ratio Rµ = B(τ − → µ− ν̄µ ντ )/B(τ − → e− ν̄e ντ ) 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
Adachi, I., Adamczyk, K., Aggarwal, L., Aihara, H., Akopov, N., Aloisio, A., et al. (2024). Test of light-lepton universality in τ decays with the Belle II experiment. JOURNAL OF HIGH ENERGY PHYSICS, 2024(8) [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/11590/489928
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