We present a measurement of R_{K^{*}}, the branching fraction ratio B(B→K^{*}μ^{+}μ^{-})/B(B→K^{*}e^{+}e^{-}), for both charged and neutral B mesons. The ratio for the charged case R_{K^{*+}} is the ...first measurement ever performed. In addition, we report absolute branching fractions for the individual modes in bins of the squared dilepton invariant mass q^{2}. The analysis is based on a data sample of 711 fb^{-1}, containing 772×10^{6} BBover ¯ events, recorded at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The obtained results are consistent with standard model expectations.
We present a search for the lepton flavor violating decays B^{+}→K^{+}τ^{±}ℓ^{∓}, with ℓ=(e,μ), using the full data sample of 772×10^{6} BBover ¯ pairs recorded by the Belle detector at the KEKB ...asymmetric-energy e^{+}e^{-} collider. We use events in which one B meson is fully reconstructed in a hadronic decay mode. We find no evidence for B^{±}→K^{±}τℓ decays and set upper limits on their branching fractions at the 90% confidence level in the (1-3)×10^{-5} range. The obtained limits are the world's best results.
We report on a search for a heavy Majorana neutrino in the decays τ^{-}→π^{-}ν_{h}, ν_{h}→π^{±}ℓ^{∓}, ℓ=e, μ. The results are obtained using the full data sample of 988 fb^{-1} collected with the ...Belle detector at the KEKB asymmetric energy e^{+}e^{-} collider, which contains 912×10^{6} ττ pairs. We observe no significant signal and set 95% CL upper limits on the couplings of the heavy right-handed neutrinos to the conventional standard model left-handed neutrinos in the mass range 0.2-1.6 GeV/c^{2}. This is the first study of a mixed couplings of heavy neutrinos to τ leptons and light-flavor leptons.
We report the status of a neural network regression model trained to extract new physics (NP) parameters in Monte Carlo (MC) simulation data. We utilize a new EvtGen NP MC generator to generate B → ...K*0µ+µ− events according to the deviation of the Wilson Coefficient C9 from its SM value, δC9. We train a three-dimensional ResNet regression model, using images built from the angular observables and the invariant mass of the di-muon system, to extract values of δC9 directly from the MC data samples. This work is intended for future analyses at the Belle II experiment but may also find applicability at other experiments.
Detectors for extreme luminosity: Belle II Adachi, I.; Browder, T.E.; Križan, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2018, Letnik:
907
Journal Article
Recenzirano
We describe the Belle II detector at the SuperKEKB electron–positron accelerator. SuperKEKB operates at the energy of the ϒ(4S) resonance where pairs of B mesons are produced in a coherent quantum ...mechanical state with no additional particles. Belle II, the first Super B factory detector, aims to achieve performance comparable to the original Belle and BaBar B factory experiments, which first measured the large CP violating effects in the B meson system, with much higher luminosity collisions and larger beam-induced backgrounds.
We present a measurement of angular observables and a test of lepton flavor universality in the B→K^{*}ℓ^{+}ℓ^{-} decay, where ℓ is either e or μ. The analysis is performed on a data sample ...corresponding to an integrated luminosity of 711 fb^{-1} containing 772×10^{6} BBover ¯ pairs, collected at the ϒ(4S) resonance with the Belle detector at the asymmetric-energy e^{+}e^{-} collider KEKB. The result is consistent with standard model (SM) expectations, where the largest discrepancy from a SM prediction is observed in the muon modes with a local significance of 2.6σ.
The experimental results on the ratios of branching fractions R(D)=B(Bover ¯→Dτ^{-}νover ¯_{τ})/B(Bover ¯→Dℓ^{-}νover ¯_{ℓ}) and R(D^{*})=B(Bover ¯→D^{*}τ^{-}νover ¯_{τ})/B(Bover ¯→D^{*}ℓ^{-}νover ...¯_{ℓ}), where ℓ denotes an electron or a muon, show a long-standing discrepancy with the standard model predictions, and might hint at a violation of lepton flavor universality. We report a new simultaneous measurement of R(D) and R(D^{*}), based on a data sample containing 772×10^{6} BBover ¯ events recorded at the ϒ(4S) resonance with the Belle detector at the KEKB e^{+}e^{-} collider. In this analysis the tag-side B meson is reconstructed in a semileptonic decay mode and the signal-side τ is reconstructed in a purely leptonic decay. The measured values are R(D)=0.307±0.037±0.016 and R(D^{*})=0.283±0.018±0.014, where the first uncertainties are statistical and the second are systematic. These results are in agreement with the standard model predictions within 0.2, 1.1, and 0.8 standard deviations for R(D), R(D^{*}), and their combination, respectively. This work constitutes the most precise measurements of R(D) and R(D^{*}) performed to date as well as the first result for R(D) based on a semileptonic tagging method.
With the full data sample of 772×106 BB¯ pairs recorded by the Belle detector at the KEKB electron-positron collider, the decay B¯→D*τ−ν¯τ is studied with the hadronic τ decays τ−→π−ντ and τ−→ρ−ντ. ...The τ polarization Pτ(D*) in two-body hadronic τ decays is measured, as well as the ratio of the branching fractions R(D*)=B(B¯→D*τ−ν¯τ)/B(B¯→D*ℓ−ν¯ℓ), where ℓ− denotes an electron or a muon. Our results, Pτ(D*)=−0.38±0.51(stat)−0.16+0.21(syst) and R(D*)=0.270±0.035(stat)−0.025+0.028(syst), are consistent with the theoretical predictions of the standard model. The polarization values of Pτ(D*)>+0.5 are excluded at the 90% confidence level.