Evidence of $\kappa$ particle in $J/\psi \to \bar{K}^*(892)^0 K^+ \pi^-$

TL;DR

This paper reports evidence for a broad $K$ resonance in $J/\psi$ decay, observed as a low mass enhancement in the $K^+\pi^-$ spectrum, supported by partial wave analysis.

Contribution

It provides experimental evidence for the $K$ particle as a broad resonance in $J/\psi$ decay, with measured mass and width, using BESI data.

Findings

Observation of a low mass enhancement in $K^+\pi^-$ spectrum.

Partial wave analysis supports the enhancement as a broad $0^{+}$ resonance.

Measured mass and width of the $K$ resonance.

Abstract

Based on a $J/\psi$ data sample of $7.8 \times 10^6$ events at BESI, the decay of $ J/\psi \to \bar{K}^*(892)^0 K^+ \pi^-$ is studied and a low mass enhancement, which is believed not coming from the phase space effect or background, is visible in the $K^+ \pi^-$ invariant mass spectrum recoiling against $\bar{K}^*(892)^0$. Partial wave analysis of this channel favors this low mass enhancement being a broad $0^{+}$ resonance with the mass and width of $771^{+164}_{-221}\pm 55$ MeV/c$^2$ and $220^{+225}_{-169} \pm 97$ MeV/c$^2$, respectively.