The BESIII collaboration reported that an anomalous line shape was observed around the ppbar mass threshold in J/ψ→γ3(π).⁺π^—) indicates the presence of a ppbar-dependent state. The article was published online Physical Examination Letters. Mass proximity up to 2 meters_P. It suggests a nucleon-antinucleon-dependent state, an idea with a long history. Before the birth of the quark model, the nucleon-antinucleon bound state had already been proposed by Professor E. Fermi and Professor KN Young.

Evidence is accumulating for anomalous behavior in the proton-antiproton system near the ppbar threshold mass; for example, J/ψ→γppabr, J/ψ→γπ⁺π^—Effective proton form factor determined by η’ and e⁺to^— →ppbar shows a narrow peak or very sharp decline around the ppbar mass threshold; this inspired much speculation and renewed interest in the nucleon–antinucleon bound state.

X(1840) is a new structure discovered in the process J/ψ→γ3(π.⁺π^—) with a sample of subjects from the BESIII experiment in 2013, also near the ppbar mass threshold. Further investigation of the shape of the X(1840) line is important to better understand its nature. Therefore, examining the 3(π) mass spectrum in the BESIII experiment⁺π^—) with an incidence of 10 billion J/ψ, approximately 45 times the size of the subsample used in the previous measurement.

The anomalous shape of the X(1840) line near the ppbar mass threshold was observed for the first time. After many trials, it was found that a model with a consistent sum of the two Breit-Wigner parameterizations could provide a good description of the data revealing a new X(1880) resonance with statistical significance greater than 10σ and mass and width. It was determined as 1882.1±1, 7±0.7 MeV/c² and 30.7±5.5±2.4 MeV/c, respectively.