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Light scalar mesons in $J / psi ->$NN$meson meson$ decays in a chiral unitary approach

We study the four-body decays $J/ψ\to N {\bar N}$ {\it meson meson} using a chiral unitary approach to account for the meson meson final state interaction (FSI). The calculation of the $J/ψ\to N \bar N π^+ π^-$ process properly reproduces the experimental data after taking the FSI of mesons and the contribution of intermediate $ρ$ meson into account. The isoscalar resonances $σ$, $f_0(980)$ and the isovector resonance $a_0(980)$ are generated through the FSI of the mesons in the channels $J/ψ\to N \bar N π^0 π^0$ and $J/ψ\to N \bar N π^0 η$, respectively. We also calculate the two mesons invariant mass distribution and the partial decay width of $J/ψ\to N \bar N K^+ K^-$ and $J/ψ\to N \bar N K^0 {\bar K}^0$, on which there is still no experimental data available.