Observation of a Resonancelike Structure in the π

Abstract

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 Γ= 45\begin+18\-13\end(stat)\begin+30\-13\end(syst)MeV.The product branching fraction is determined to be B(B^0→ K^∓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 ×10^6 B\bar{B} pairs collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric energy e^+e^- collider.journal articl