Triangle mechanism in the decay process $J/\psi \to K^- K^+ a_1(1260)$

TL;DR

This paper investigates how the triangle mechanism influences the decay of J/psi into K- K+ a1(1260), revealing a triangle singularity and sizable branching ratios that can be tested experimentally to learn about the a1(1260) resonance.

Contribution

It introduces the role of the triangle mechanism in J/psi decay, showing how it generates a triangle singularity and predicts measurable branching ratios for experimental verification.

Findings

Triangle singularity around 1920 MeV in the decay process.

Predicted branching ratios: 1.210 x 10^-5 and 3.501 x 10^-5.

Potential for experimental observation at BESIII, LHCb, and Belle-II.

Abstract

The role of triangle mechanism in the decay process $J/\psi \to K^- K^+ a_1(1260)$ is probed. In this mechanism, a close-up resonance with mass $1823$ MeV and width $122$ MeV decays into $K^* \phi, K^* \to K \pi$ and then $K^* \bar{K}$ fuses into the $a_1(1260)$ resonance. We find that this mechanism leads to a triangle singularity around $M_{\rm inv}(K^- a_1(1260))\approx 1920$ MeV, where the axial-vector meson $a_1(1260)$ is considered as a dynamically generated resonance. With the help of the triangle mechanism we find sizable branching ratios $\text{Br}(J/\psi \to K^- K^+ a_1(1260),a_1 \to \pi \rho)=1.210 \times 10^{-5}$ and $\text{Br}(J/\psi \to K^- K^+ a_1(1260))=3.501 \times 10^{-5}$. Such a effect from triangle mechanism of the decay process could be investigated by such as BESIII, LHCb and Belle-II experiments. This potential investigation can help us obtain the information of the axial-vector meson $a_1(1260)$.