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

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.

Figures (3)

• Figure 1: The $M^2(K\pi)$ (horizontal) vs.$M^2(\pi\psi ')$ (vertical) Dalitz-plot distribution for $B^0\rightarrow K^-\pi^+\psi '$ candidate events.
• Figure 2: The $M(\pi^+\psi ')$ distribution for events in the $M_{\rm bc}$-$\Delta E$ signal region and with the $K^*$ veto applied. The shaded histogram show the scaled results from the $\Delta E$ sideband. The solid curves show the results of the fit described in the text.
• Figure 3: The $M(K\pi)$ distribution for events within $\pm 0.03$ GeV of the 4.43 GeV peak. Here the $K^*$ veto, which excludes the regions indicated by double-sided arrows, has been removed. The shaded histogram indicates the $\Delta E$-sideband-determined non-$B$ background.