Partial wave analysis of J/\psi \to \gamma \phi \phi

TL;DR

This study analyzes the decay of J/psi particles into a photon and phi mesons, revealing a new structure near 2.24 GeV/c^2 dominated by an eta(2225) state, using a large dataset from BESII.

Contribution

First partial wave analysis of J/psi to gamma phi phi decay, identifying the eta(2225) resonance with specific mass, width, and branching fraction.

Findings

Observed near-threshold enhancement in phi phi invariant mass.

Identified eta(2225) as the dominant state with precise mass and width.

Measured the product branching fraction of the decay process.

Abstract

Using $5.8 \times 10^7 J/\psi$ events collected in the BESII detector, the radiative decay $J/\psi \to \gamma \phi \phi \to \gamma K^+ K^- K^0_S K^0_L$ is studied. The $\phi\phi$ invariant mass distribution exhibits a near-threshold enhancement that peaks around 2.24 GeV/$c^{2}$. A partial wave analysis shows that the structure is dominated by a $0^{-+}$ state ($\eta(2225)$) with a mass of $2.24^{+0.03}_{-0.02}{}^{+0.03}_{-0.02}$ GeV/$c^{2}$ and a width of $0.19 \pm 0.03^{+0.06}_{-0.04}$ GeV/$c^{2}$. The product branching fraction is: $Br(J/\psi \to \gamma \eta(2225))\cdot Br(\eta(2225)\to \phi\phi) = (4.4 \pm 0.4 \pm 0.8)\times 10^{-4}$.