Observation of a near-threshold enhancement in th p pbar mass spectrum from radiative J/psi-->gamma p pbar decays

TL;DR

This paper reports the observation of a narrow enhancement near the proton-antiproton mass threshold in radiative J/psi decays, suggesting a possible new state or phenomenon.

Contribution

First observation of a near-threshold ppbar enhancement in J/psi radiative decays with detailed mass and width analysis.

Findings

Enhancement near 2mp in ppbar spectrum

Peak mass below 2mp threshold

Width less than 30 MeV

Abstract

We observe a narrow enhancement near 2mp in the invariant mass spectrum of ppbar pairs from radiative J/psi-->gamma ppbar decays. The enhancement can be fit with either an S- or P-wave Breit Wigner fuction. In the case of the S-wave fit, the peak mass is below the 2mp threshold and the full width is less than 30 MeV. These mass and width values are not consistent with the properties of any known meson resonance.