Search for lepton-flavor-violating τ^- → ℓ^- K_s⁰ decays at Belle and Belle II

2025/04/22 by Belle, Collaborations, Belle II, : +419
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex)

paper · doi:10.48550/arxiv.2504.15745

Abstract

We present the results of a search for charged-lepton-flavor violating decays τ^- → ℓ^-K_S⁰, where ℓ^- is either an electron or a muon. We combine e⁺e^- data samples recorded by the Belle II experiment at the SuperKEKB collider (428 fb^-1) with samples recorded by the Belle experiment at the KEKB collider (980 fb^-1) to obtain a sample of 1.3 billion e⁺e^-→τ⁺τ^- events. We observe 0 and 1 events and set 90% confidence level upper limits of 0.8 × 10^-8 and 1.2 × 10^-8 on the branching fractions of the decay modes τ^- → e^-K_S⁰ and τ^- → μ^-K_S⁰, respectively. These are the most stringent upper limits to date.

Related

• Search for the lepton-flavor-violating τ^- → e^∓ ℓ^± ℓ^∓ decays at Belle II
• Search for lepton-flavor-violating τ^- → ℓ^-ϕ decays in 2019-2021 Belle II data
• Search for lepton flavor violating τ→ ℓ V⁰ decays at Belle
• Search for lepton flavor-violating decay modes B⁰ → K^{∗ 0}τ^±ℓ^∓ (ℓ = e,μ) with hadronic B-tagging at Belle and Belle II
• Search for lepton-flavor-violating tau decays to ℓα at Belle