Observation of a resonancelike structure in the π+-ψ′ mass distribution in exclusive B→Kπ+-ψ′ decays

A distinct peak is observed in the pi(+/-)psi' invariant mass distribution near 4.43 GeV in B -> K pi(+/-)psi' decays. A fit using a Breit-Wigner resonance shape yields a peak mass and width of M=4433 +/- 4(stat)+/- 2(syst) MeV and Gamma=45(-13)(+18)(stat)(-13)(+30)(syst) MeV. The product branching fraction is determined to be B(B(0)-> K(-/+)Z(+/-)(4430))xB(Z(+/-)(4430)->pi(+/-)psi')=(4.1 +/- 1.0(stat)+/- 1.4(syst))x10(-5), where Z(+/-)(4430) is used to denote the observed structure. The statistical significance of the observed peak is 6.5 sigma. These results are obtained from a 605 fb(-1) data sample that contains 657x10(6) B (B) over bar pairs collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e(+)e(-) collider.