Observation of a resonance-like structure in the π ±ψ' mass distribution in exclusive B → Kπ±ψ' decays
A distinct peak is observed in the π±ψ' invariant mass distribution near 4.43 GeV in B → Kπ±ψ' decays. A fit using a Breit-Wigner resonance shape yields a peak mass and width of M = 4433 ± 4 (stat) ± 2 (syst) MeV and F = 45+18 -13 (stat)+30-13 (syst) MeV. The product branching fraction is determined to be B(B0 → K±Z± (4430)) × B(Z±(4430) → π±ψ') = (4.1 ± 1.0(stat) ± 1.4(syst)) × 10-5, where Z±(4430) is used to denote the observed structure. The statistical significance of the observed peak is 6.5σ. These results are obtained from a 605 fb-1 data sample that contains 657 million B ̄B pairs collected near the γ(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider.