The Beijing Spectrometer(BESIII)Collaboration reconstructed the invariant mass of three pairs of positive and negative pions by studying the decay process of charmonium to a photon and three pairs of positive and negative pions.They discovered the resonant structures X(1840)and X(1880),which were initially found in the earlier experimental work of proton and anti-proton spectrum in J/Ψ→γ+p+(p)decay and η'π+π decay channels in J/Ψdecay by the BES Collaboration in 2003 and 2005.The experimental results of this important work further confirm the existence of new particles,which are interpreted as the predicted proton-antiproton bound states,also known as protonium.This paper briefly introduces the experimental discovery processes of these resonant structures and discusses the theoretical explorations inspired by them.The predictions proposed by these theoretical explorations offer a new perspective for studying the nature of these particles and new decay modes.For example,Yan Mulin,along with his collaborators,made significant contributions to the theoretical exploration of the X(p(p))structure direction using proton-antiproton bound states.Starting from the theoretical background of viewing protons as skyrmions,this group discussed a system composed of a skymion and an anti-skyrmion,discovering a bound state solution for the skyrmion and anti-skyrmion system,which can explain the bound state of proton and antiproton.They then constructed a phenomenological potential model for a proton and an antiproton,which can calculate the mass and width of the bound state by adjusting parameters,interpreting X(p(p))as the bound state of a proton and an antiproton,namely protonium.Additionally,based on experimental phenomena of producing multiple mesons in low-energy proton-antiproton collisions,this group explicitly predicted another decay channel of X(p(p))as a proton-antiproton bound state,decaying into 4 to 7 mesons instead of 2-3 mesons.The recent analysis by BESIII Collaboration of the decay process of charmonium to a photon and three pairs of positive and negative pions can be seen as a specific realization of proton-antiproton bound states decaying into 6 mesons.The experimental results are consistent with this theoretical prediction.Conversely,this theoretical prediction strengthens the viewpoint of interpreting the resonant states X(1840)and X(1880)discovered by BESIII as protoniums.Other theoretical work also helped the experimental analyses by the BES Collaboration.Therefore the collaborative exploration of experiments and theory plays a positive role in deepening understanding of the fundamental laws of nature.
Beijing SpectrometerBeijing Electron Positron Colliderprotoniumresonance
马伯强
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北京大学物理学院,北京 100871
Beijing Spectrometer Beijing Electron Positron Collider protonium resonance
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