Observation of a ppb mass threshoud enhancement in ψ^\prime\toπ^+π^-J/ψ(J/ψ\toγp\bar{p}) decay
The decay channel $ψ^\prime\toπ^+π^-J/ψ(J/ψ\toγp\bar{p})$ is studied using a sample of $1.06\times 10^8$ $ψ^\prime$ events collected by the BESIII experiment at BEPCII. A strong enhancement at threshold is observed in the $p\bar{p}$ invariant mass spectrum. The enhancement can be fit with an $S$-wave Breit-Wigner resonance function with a resulting peak mass of $M=1861^{+6}_{-13} {\rm (stat)}^{+7}_{-26} {\rm (syst)} {\rm MeV/}c^2$ and a narrow width that is $Γ<38 {\rm MeV/}c^2$ at the 90% confidence level. These results are consistent with published BESII results. These mass and width values do not match with those of any known meson resonance.
hep-ex↗