The close proximity to the mass of 2mp suggests the existence of nucleon-antinucleon bound states, a concept with a rich history. Even before the Quark Model was established, the idea of a nucleon-antinucleon bound state was put forth by Prof. E. Fermi and Prof. C. N. Yang.
There is a growing body of evidence pointing towards unusual behavior in the proton-antiproton system near the ppbar mass threshold. This includes observations such as J/ψ→γppabr, J/ψ→γπ+π-η’, and the proton’s form factor from e+e-→ppbar, showing a distinct peak or rapid decline around the ppbar mass threshold. These findings have sparked various speculations and reignited interest in the nucleon-antinucleon bound state.
The discovery of X(1840) in the J/ψ→γ3(π+π-) process in 2013, near the ppbar mass threshold, has opened up new avenues for exploration. To gain a deeper understanding of X(1840), the BESIII experiment conducted a detailed analysis of the 3(π+π-) mass spectrum using a significantly larger dataset of 10 billion J/ψ events, surpassing previous measurements by 45 times.
An unusual line shape of X(1840) near the ppbar mass threshold was identified for the first time. Through rigorous analysis, a model combining two Breit-Wigner parameterizations was able to accurately describe the data, revealing a novel resonance X(1880) with a statistical significance exceeding 10σ. The mass and width of X(1880) were determined to be 1882.1±1.7±0.7 MeV/c2 and 30.7±5.5±2.4 MeV/c, respectively.
2024-04-12 23:00:02
Source from phys.org