Observation of a Near-Threshold Enhancement in thepp¯Mass Spectrum from RadiativeJ/ψ→γpp¯

Abstract

We observe a narrow enhancement near 2m(p) in the invariant mass spectrum of pp pairs from radiative J/psi-->gammapp decays. No similar structure is seen in J/psi-->pi(0)pp decays. The results are based on an analysis of a 58 x 10(6) event sample of J/psi decays accumulated with the BESII detector at the Beijing electron-positron collider. The enhancement can be fit with either an S- or P-wave Breit-Wigner resonance function. In the case of the S-wave fit, the peak mass is below 2m(p) at M=1859(+3)(-10) (stat)+5-25(syst) MeV/c(2) and the total width is Gamma<30 MeV/c(2) at the 90% confidence level. These mass and width values are not consistent with the properties of any known particle.

The hidden-charm pentaquark and tetraquark states

“…• In 2003, the X(1835) was observed by the BESII Collaboration in the pp mass spectrum of the J/ψ → γpp radiative decay [193], with mass M = (1859 +3 −10…”

Status of X(1835) and pp¯ Interaction from Chiral Symmetry

“…[19]), a good description of BES data was obtained [20], where C is fitted to data as a free parameter. BES also measured J/ψ → π pp decay but did not observe the strong threshold enhancement [1]. In this channel, the pp occurs in isospin-1 3 S 1 , i.e., I = 1, S = 1, the interaction considered in Ref.…”

“…Data are taken from Refs. [1,39,40] and normalized to the one given by BES2012 [40]. Figure from Ref.…”

“…With a large accumulation of J/ψ data, a prominent pp-threshold enhancement is reported by BES collaboration [1].…”

“…Concerning its nature, it is still quite controversial so far. In the analysis of BES themselves, they used a new resonance (BW form) [1] to describe the peak observed around nucleon antinucleon (NN) threshold, which is 1877 MeV [2]. Due to the proximity of the NN threshold, the common conjecture will be naturally whether it has something to do with NN interaction, or more interestingly, NN bound state (baryonium).…”