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A<sc>bstract</sc> We report a search for the charged-lepton flavor violation in Υ(2S) →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 ($$ \mathcal{B} $$ ) at 90% confidence level. We obtain the most stringent upper limits:$$ \mathcal{B} $$ (Υ(2S)→ μ∓τ±)<0.23×10−6and$$ \mathcal{B} $$ (Υ(2S)→ e∓τ±)<1.12×10−6.more » « less
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We measure the branching fraction of the decay using data collected with the Belle II detector. The data contain 387 million pairs produced in collisions at the resonance. We reconstruct decays from an analysis of the distributions of the energy and the helicity angle. We determine the branching fraction to be , in agreement with previous results. Our measurement improves the relative precision of the world average by more than a factor of two. Published by the American Physical Society2024more » « lessFree, publicly-accessible full text available June 1, 2025
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We report on a search for a resonance decaying to a pair of muons in events in the mass range, using of data collected by the Belle II experiment at the SuperKEKB collider at a center of mass energy of 10.58 GeV. The analysis probes two different models of beyond the standard model: a vector boson in the model and a muonphilic scalar. We observe no evidence for a signal and set exclusion limits at the 90% confidence level on the products of cross section and branching fraction for these processes, ranging from 0.046 fb to 0.97 fb for the model and from 0.055 fb to 1.3 fb for the muonphilic scalar model. For masses below , the corresponding constraints on the couplings of these processes to the standard model range from 0.0008 to 0.039 for the model and from 0.0018 to 0.040 for the muonphilic scalar model. These are the first constraints on the muonphilic scalar from a dedicated search. Published by the American Physical Society2024more » « lessFree, publicly-accessible full text available June 1, 2025
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Free, publicly-accessible full text available January 1, 2026
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A search is presented for an extended Higgs sector with two new particles, and , in the process . Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at collected with the CMS detector, corresponding to an integrated luminosity of . No evidence of such resonances is seen. Upper limits are set on the production cross section for between 300 and 3000 GeV and between 0.5% and 2.5%, representing the most sensitive search in this channel. © 2025 CERN, for the CMS Collaboration2025CERNmore » « lessFree, publicly-accessible full text available January 1, 2026
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We measure the tau-to-light-lepton ratio of inclusive -meson branching fractions , where indicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed meson and a charged lepton candidate from of electron-positron collision data collected with the Belle II detector. We find , in agreement with standard-model expectations. This is the first direct measurement of . Published by the American Physical Society2024more » « less
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A<sc>bstract</sc> We present a search for the lepton-flavor-violating decays$$ {B}_s^0 $$ →ℓ∓τ±, whereℓ=e, μ, using the full data sample of 121 fb−1collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energye+e−collider. We use$$ {B}_s^0{\overline{B}}_s^0 $$ events in which one$$ {B}_s^0 $$ meson is reconstructed in a semileptonic decay mode and the other in the signal mode. We find no evidence for$$ {B}_s^0 $$ → ℓ∓τ±decays and set upper limits on their branching fractions at 90% confidence level as$$ \mathcal{B} $$ ($$ {B}_s^0 $$ → e∓τ±)<14×10−4and$$ \mathcal{B} $$ ($$ {B}_s^0 $$ → μ∓τ±)<7.3×10−4. Our result represents the first upper limit on the$$ {B}_s^0 $$ → e∓τ±decay rate.more » « less