Observation of a resonance-like structure in the pi^+- psi' mass distribution in exclusive B-->K pi^+- psi' decays

TL;DR

This paper reports the observation of a resonance-like structure, Z(4430), in the pi^+/- psi' mass distribution from B decays, with a significance of 6.5 sigma, indicating a possible new exotic state.

Contribution

First observation of a resonance-like structure Z(4430) in B decays with detailed mass, width, and branching fraction measurements.

Findings

Resonance mass near 4433 MeV

Width of approximately 45 MeV

Statistical significance of 6.5 sigma

Abstract

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 4433+-4(stat)+-2(syst) MeV and Gamma = 45^+18_-13(stat) ^+30_-13 MeV. The product branching fraction is determined to be Bf(B-->KZ(4430))xBf(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 6.5sigma. These results are obtained from a 605 fb-1 data sample that contains 657 million BBbar pairs collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider.