33 research outputs found
Measurement of branching fractions of , , , and
International audienceWe report branching fraction measurements of four decay modes of the Λc+ baryon, each of which includes an η meson and a Λ baryon in the final state, and all of which are measured relative to the Λc+→pK-π+ decay mode. The results are based on a 980 fb-1 data sample collected by the Belle detector at the KEKB asymmetric-energy e+e- collider. Two decays, Λc+→ηΣ0π+ and Λ(1670)π+, are observed for the first time, while the measurements of the other decay modes, Λc+→ηΛπ+ and ηΣ(1385)+, are more precise than those made previously. We obtain relative branching fractions of B(Λc+→ηΛπ+)/B(Λc+→pK-π+)=0.293±0.003±0.014, B(Λc+→ηΣ0π+)/B(Λc+→pK-π+)=0.120±0.006±0.010, B(Λc+→Λ(1670)π+)×B(Λ(1670)→ηΛ)/B(Λc+→pK-π+)=(5.54±0.29±0.73)×10-2, and B(Λc+→ηΣ(1385)+)/B(Λc+→pK-π+)=0.192±0.006±0.016. The mass and width of the Λ(1670) are also precisely determined to be 1674.3±0.8±4.9 MeV/c2 and 36.1±2.4±4.8 MeV, respectively, where the uncertainties are statistical and systematic, respectively
Measurement of and with a semileptonic tagging method
We report a measurement of the ratios of branching fractions and , where denotes an electron or a muon. The results are based on a data sample containing events recorded at the resonance with the Belle detector at the KEKB collider. The analysis utilizes a method where the tag-side meson is reconstructed in a semileptonic decay mode, and the signal-side is reconstructed in a purely leptonic decay. The measured values are and , where the first uncertainties are statistical and the second are systematic. These results are in agreement with the Standard Model predictions within and standard deviations, respectively, while their combination agrees with the Standard Model predictions within standard deviations
Test of lepton flavor universality in decays at Belle
We present a measurement of , the ratio of the branching fractions and , for both charged and neutral mesons. The ratio for charged mesons, , is the first measurement ever performed. The analysis is based on a data sample of , containing events, recorded at the resonance with the Belle detector at the KEKB asymmetric-energy collider
Test of lepton flavor universality and search for lepton flavor violation in decays
International audienceWe present measurements of the branching fractions for the decays B → Kμμ and B → Kee, and their ratio (R), using a data sample of 711 fb that contains 772 × 10 events. The data were collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy ee collider. The ratio R is measured in five bins of dilepton invariant-mass-squared (q): q ∈ (0.1, 4.0), (4.00, 8.12), (1.0, 6.0), (10.2, 12.8) and (> 14.18) GeV/c, along with the whole q region. The R value for q ∈ (1.0, 6.0) GeV/c is ± 0.01. The first and second uncertainties listed are statistical and systematic, respectively. All results for R are consistent with Standard Model predictions. We also measure CP-averaged isospin asymmetries in the same q bins. The results are consistent with a null asymmetry, with the largest difference of 2.6 standard deviations occurring for the q ∈ (1.0, 6.0) GeV/c bin in the mode with muon final states. The measured differential branching fractions, /dq, are consistent with theoretical predictions for charged B decays, while the corresponding values are below the expectations for neutral B decays. We have also searched for lepton-flavor-violating B → Kμe decays and set 90% confidence-level upper limits on the branching fraction in the range of 10 for B → Kμe, and B → Kμe modes.[graphic not available: see fulltext