Dalitz analysis of B --> K pi psi' decays and the Z(4430)+

TL;DR

This paper presents a Dalitz plot analysis of B --> K pi psi' decays, confirming the Z(4430)+ state with precise measurements of its properties and branching fractions, using a large data sample from the Belle detector.

Contribution

It provides the first detailed Dalitz analysis confirming the Z(4430)+ state and measures its mass, width, and branching fractions with high significance.

Findings

Z(4430)+ signal with 6.4 sigma significance

Measured Z(4430)+ mass and width: 4443 MeV/c^2 and 107 MeV

Determined branching fraction of B0 --> K- Z(4430)+ and polarization of K*(892)^0

Abstract

From a Dalitz plot analysis of B --> K pi psi' decays, we find a signal for Z(4430)+ --> pi+ psi' with a mass M= (4443(+15-12)(+19-13))MeV/c^2, width Gamma= (107(+86-43)(+74-56))MeV, product branching fraction BR(B0 --> K- Z(4430)+) x BR(Z(4430)+ --> pi+ psi')= (3.2(+1.8-0.9)(+5.3-1.6)) x 10^{-5}, and significance of 6.4sigma that agrees with previous Belle measurements based on the same data sample. In addition, we determine the branching fraction BR(B^0 --> K*(892)^0 psi')= (5.52(+0.35-0.32)(+0.53-0.58)) x 10^{-4} and the fraction of K*(892)^0 mesons that are longitudinally polarized f_L= 44.8(+4.0-2.7)(+4.0-5.3)%. These results are obtained from a 605fb^{-1} data sample that contains 657 million B-anti-B pairs collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider.