Study J/ψâ†'γπ~+Ï€~-Ï€~+Ï€~-Ï€~+Ï€~-Decay At BESâ…¢

Within the quark model, hadron is either a meson which composed of one quark andone anti-quark or a baryon which composed of three quarks. Within the framework of QCD,because of existence of gluon self-coupling, in addition to conventional messon and baryonstates, there may exist bound states such as glueball (composed of gluons), hybrid states(composed of quarks and gluons) and multi-quark states (more than three quarks). But inexperiment, the existence of these new hadrons are not confirmed.The J/ψ particle has always been regarded as the ideal laboratory to study the lighthadron spectroscopy and search for new hadrons since it was discovered in1974. X(1835)was observed at BESII in2005and immediately aroused the attention of the hight energyphysicists. Some scientists regarded X(1835) as a proton anti-proton bound state, the sixquarks station. And at BESâ…¢ the X(1835) was confirmed and tow new resonances X(2120)and X(2370) were observed. To search for the new decay modes of these resonances, westudy the mode of J/ψâ†'γπ⁺Ï€^-Ï€⁺Ï€^-Ï€⁺Ï€^-.With a sample of225million J/ψ taken at the BESâ…¢ detector, the decay ofJ/ψâ†'γπ⁺Ï€^-Ï€⁺Ï€^-Ï€⁺Ï€^-is analyzed. A resonance around1.84GeV/c²with statisticalsignificance of7.6σ is observed in the Ï€⁺Ï€^-Ï€⁺Ï€^-Ï€⁺Ï€^-invariant mass spectrum. A fit witha simple Breit-Wigner convoluted with a Gaussian function yields M=1842.2±4.2+6.8-1.0MeV/c2and Γ=83±14+910MeV/c2. Its mass is consistent with that of X(1835)within one standard deviation, while the width is much smaller than that of X(1835)measured at BESâ…¢. The product branching fraction is determined to be B(J/ψâ†'γX(1840))B(X(1840)â†'Ï€⁺Ï€^-Ï€⁺Ï€^-Ï€⁺Ï€^-)=(2.40±0.35+0.4350.72)×10^-5. No η' signal wasobserved in theÏ€⁺Ï€^-Ï€⁺Ï€^-Ï€⁺Ï€^-invariant mass spectrum and the branching fraction upperlimit of η'â†'Ï€⁺Ï€^-Ï€⁺Ï€^-Ï€⁺Ï€^-is B(η'â†'Ï€⁺Ï€^-Ï€⁺Ï€^-Ï€⁺Ï€^-)<3×10^-5 at90%confidencelevel.