Search For ?'???? At BES?

The Beijing Spectrometer III(BES?),operating at the Beijing Electron Positron Collider?(BEPCII),is a general purpose detector,which is designed for(?)-charm physics.At present,a sample of 1.31×109J/?events was accumulated at the BESIII detector,and with the advantages of low background,simple topology of final states and high detection efficiency,the world's largest samples of J/? events offer a unique opportunity to study light meson spectroscopy and light meson decays via charmonium decays.The ?' meson provides a unique place for understanding the distinct symmetry-breaking meehanisms in low-cnergy Quantum Cnrodynamics(QCD)and its decays play an important role in exploring the effective theory of QCD at low energy.Based on the frameworks of the chiral-loop,Liner ? Model(L?)and the Vector Meson Dominance(VMD)model,the branch-ing fraction of decays ?'???? was predicted to be 2.6×10-4,and the dominant contribution is from the VMD.The branching fraction of J/????'(5.15±0.16)×10-3,is quite large.At present,a sample of 1.31×109 J/? events was collected with the BESIII detector,corresponding to 6.75×106?'events,which offers an opportunity to explore the vU rare decays.In this thesis,we performed a search for ?'???? via J/????'for the first time.No evident ?' signal is observed in the ??? invariant mass spectrum.Using the Bayesian approach,the upper limit on the branching fraction of ?'???? is determined to be 1.18×10-4 at the 90%confidence level.Of interest is the upper limit is lower than the theoretical prediction by a factor of 2.Most recently another sample of 3.7×109 J/? events was collected at the BESIII detector,which allows us to make a further investigation on the decay of?'????.The new result is then expected to have a strong constraint on the theoretical models.