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Free, publicly-accessible full text available February 1, 2025
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A bstract We report a search for the charged-lepton flavor violation in Υ(2
S ) →ℓ ∓τ ± (ℓ =e, μ ) decays using a 25 fb− 1Υ(2S ) sample collected by the Belle detector at the KEKBe +e − asymmetric-energy collider. We find no evidence for a signal and set upper limits on the branching fractions ( ) at 90% confidence level. We obtain the most stringent upper limits:$$ \mathcal{B} $$ (Υ(2$$ \mathcal{B} $$ S )→ μ ∓τ ± )< 0. 23× 10− 6and (Υ(2$$ \mathcal{B} $$ S )→ e ∓τ ± )< 1. 12× 10− 6.Free, publicly-accessible full text available February 1, 2025 -
Free, publicly-accessible full text available December 1, 2024
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Free, publicly-accessible full text available December 1, 2024
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Free, publicly-accessible full text available December 1, 2024
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A bstract We measure the cross section of
e +e − →η c J/ψ at the Υ(nS )(n = 1–5) on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected by the Belle detector with an integrated luminosity of 955 fb− 1. We also search for double charmonium production ine +e − →η c J/ψ via initial state radiation near theη c J/ψ threshold. No evident signal of the double charmonium state is found, but evidence for thee +e − → η c J/ψ process is found with a statistical significance greater than 3. 3σ near theη c J/ψ threshold. The average cross section near the threshold is measured and upper limits of cross sections are set for other regions.