Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher.
Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?
Some links on this page may take you to non-federal websites. Their policies may differ from this site.
-
Free, publicly-accessible full text available March 1, 2025
-
Free, publicly-accessible full text available February 1, 2025
-
Free, publicly-accessible full text available December 1, 2024
-
Free, publicly-accessible full text available December 1, 2024
-
We report on a search for a resonancedecaying to a pair of muons inevents in themass range, usingof 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 ofbeyond the standard model: avector boson in themodel 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 themodel 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 themodel 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 Society 2024 Free, publicly-accessible full text available June 1, 2025 -
We report a measurement of decay-time-dependent charge-parity () asymmetries indecays. We usepairs collected at theresonance with the Belle II detector at the SuperKEKB asymmetric-energy electron-positron collider. We reconstruct 220 signal events and extract the-violating parametersandfrom a fit to the distribution of the decay-time difference between the twomesons. The resulting confidence region is consistent with previous measurements inanddecays and with predictions based on the standard model.
Published by the American Physical Society 2024 Free, publicly-accessible full text available June 1, 2025 -
We search for the rare decayin asample of electron-positron collisions at theresonance collected with the Belle II detector at the SuperKEKB collider. We use the inclusive properties of the accompanyingmeson inevents to suppress background from other decays of the signalcandidate and light-quark pair production. We validate the measurement with an auxiliary analysis based on a conventional hadronic reconstruction of the accompanyingmeson. For background suppression, we exploit distinct signal features using machine learning methods tuned with simulated data. The signal-reconstruction efficiency and background suppression are validated through various control channels. The branching fraction is extracted in a maximum likelihood fit. Our inclusive and hadronic analyses yield consistent results for thebranching fraction ofand, respectively. Combining the results, we determine the branching fraction of the decayto be, providing the first evidence for this decay at 3.5 standard deviations. The combined result is 2.7 standard deviations above the standard model expectation.
Published by the American Physical Society 2024 Free, publicly-accessible full text available June 1, 2025 -
We measure the tau-to-light-lepton ratio of inclusive-meson branching fractions, whereindicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructedmeson and a charged lepton candidate fromof 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 Society 2024 Free, publicly-accessible full text available May 1, 2025 -
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.