No abstract

We report a measurement of the process γγ * → π 0 with a 759 fb −1 data sample recorded with the Belle detector at the KEKB asymmetric-energy e + e − collider. The pion transition form factor, F (Q 2 ), is measured for the kinematical region 4 GeVGeV 2 , where −Q 2 is the invariant mass squared of a virtual photon. The measured values of Q 2 |F (Q 2 )| agree well with the previous measurements below Q 2 ≃ 9 GeV 2 but do not exhibit the rapid growth in the higher Q 2 region seen in another recent measurement, which exceeds the asymptotic QCD expectation by as much as 50%.

We report the observation of two narrow structures in the mass spectra of the π(±)Υ(nS) (n=1, 2, 3) and π(±)h(b)(mP) (m=1, 2) pairs that are produced in association with a single charged pion in Υ(5S) decays. The measured masses and widths of the two structures averaged over the five final states are M(1)=(10,607.2±2.0)  MeV/c2, Γ(1)=(18.4±2.4)  MeV, and M(2)=(10,652.2±1.5)  MeV/c2, Γ(2)=(11.5±2.2)  MeV. The results are obtained with a 121.4  fb(-1) data sample collected with the Belle detector in the vicinity of the Υ(5S) resonance at the KEKB asymmetric-energy e+ e- collider.

We report the results of a study of the exclusive semileptonic decays B − → π 0 ℓ −ν ℓ ,B 0 → π + ℓ −ν ℓ , B − → ρ 0 ℓ −ν ℓ ,B 0 → ρ + ℓ −ν ℓ and B − → ωℓ −ν ℓ , where ℓ represents an electron or a muon. The events are tagged by fully reconstructing a second B meson in the event in a hadronic decay mode. The measured branching fractions are B(B − → π 0 ℓ −ν ℓ) = (0.80 ± 0.08 ± 0.04) × 10 −4 , B(B 0 → π + ℓ −ν ℓ) = (1.49 ± 0.09 ± 0.07) × 10 −4 , B(B − → ρ 0 ℓ −ν ℓ) = (1.83 ± 0.10 ± 0.10) × 10 −4 , B(B 0 → ρ + ℓ −ν ℓ) = (3.22 ± 0.27 ± 0.24) × 10 −4 , and B(B − → ωℓ −ν ℓ) = (1.07 ± 0.16 ± 0.07) × 10 −4 , where the first error is statistical and the second one is systematic. The obtained branching fractions are inclusive of soft photon emission. We also determine the branching fractions as a function of the 4-momentum transfer squared to the leptonic system q 2 = (p ℓ + p ν) 2 , where p ℓ and p ν are the lepton and neutrino 4-momenta, respectively. Using the pion modes, a recent LCSR calculation, lattice QCD results and a model-independent description of the hadronic form factor, a value of the CKM matrix element |V ub | = (3.52 ± 0.29) × 10 −3 is extracted. For the first time, a charmless state with invariant mass greater than 1 GeV/c 2 , which might be dominated by the decay B − → f 2 ℓ −ν ℓ , is observed. These results are obtained from a 711 fb −1 data sample that contains 772 × 10 6 BB pairs, collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider.

We report on a search for heavy neutrinos in B-meson decays. The results are obtained using a data sample that contains 772 × 10 6 B B pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. No signal is observed and upper limits are set on mixing of heavy neutrinos with left-handed neutrinos of the Standard Model in the mass range 0.5 GeV/c 2 − 5.0 GeV/c 2 .