Search For Invisible Decays Of η/η’ And Electromagnetic Transitions J/ψ�'Pl+l-

Recently,the excess of electrons and positions measured by PAMELA,PPBBETS, ATIC and other experiments can be explained as interaction between a new light bo-son and dark matter.The measurements of INTERGRAL telescope,DAMA/NaI and DAMA/LIBRA experiments are suggestive of annihilation of light(?)(1～100)MeV dark matter and dark matter-nucleus inelastic scattering with dark matter mass splitting. Theoretically,a new U boson is proposed,which has a kinetic mixing with Standard Model electromagnetic propagator photon.U boson is a bridge between Standard Mod-el particles and dark matter,therefore existence of U should be searched with process: two standard model fermions annihilate to U boson,then U decays to two light dark matter particles.Since interaction between dark matter or neutrino and detector can not be detected by BESIII,measurement of invisible decay of quarkonium is feasible and decay rate of quarkonium to neutrino and antineutrino can also studied.About225M J/ψdata have been collected by BESIII,which are used to study invisible decay ofη/η1andη/η1�'γγ.η/η1�'γγ.1comes from two-body decayJ/ψ�'φ(K+K-)η/η.The ratio of branching fraction obtained at90％C.L.is(?)<3.37×10-4/2.39×10-2,the corresponding branching fraction of η/η1invisible decay is:Br(η/η1�'invisible)<1.32×10-4/5.31×10-4.These results are more improvement than ones from BESII:Br(η/η1�'invisible)<6.0×10-4/1.4×10-3. But these results do not reach the order of theoretical prediction:η/η1�'vv～10-11, η/η1�'XX～1.4×10-5/8.1×10-7.These values are the best results in the world.The electromagnetic(EM)Dalitz decay V�'Pl+l-of light vector mesons have been studied by NA60,SND,KLOE-2and other experiments.The ratios of EM Dalitz decays to the corresponding radiative decays of vector mesons are suppressed by two orders of magnitude,and are modified by form factor of EM transition V�'P.The measurements of form factor show that pole mass obtained by some experiment de-viates from theoretical value,if form factor is parameterized with pole approximation based on Vector Dominance Model(VDM).So study of EM Dalitz decays of charmo-nium J/ψ�'pl+l-will provide useful information to understand interaction between charmonium state and EM field.Moreover, the invariant mass spectrum of lepton pair l+l-could be used to search for U/Z"boson with mass less than300MeV.Theoretically,angular distribution q2-dependent decay rates are obtained. With usual pole approximation of form factor,the corresponding Dalitz decay rate are: Br(J/ψ�'πoe+e-)=(3.89(?))×10-7,Br(J/ψ�'πoμ+μ-)=(?)×10-7； Br(J/ψ�'πe+e-)=(1.21±0.04)×10-7,Br(J/ψ�'ημ+μ-)=(0.30±0.01)×10-5；Br((J/ψ�'η1e+e-)=(5.66±0.16)×10-5,Br((J/ψ�'η1μ+μ-)=(1.31±0.04)×10-5.Experimentally,with225M J/ψdata three decay channels are preliminarily mea-sured for the first time in the world:J/ψ�'e+e-η1(γρ),J/ψ�'e+e-η(πoπ+π-),J/ψ ψ�'e+e-η1(η(γγ)π+π-)。We measured the branching fractions of these channels pre-liminarily:Br(J/ψ�'πe+e-η1)=(4.99±0.58)×10-5,Br(J/ψ�'e+e-η)(0.94±0.18)×10-5,which are consistent with theoretical results.