Search For The Radiative Transitions And Invisible Decays Of CharMonia

Charmonium spectrum and decays are an ideal place for studying the strong in-teraction dynamics in the interplay of perturbative and non-perturbative QCD regime. In the past decades there have been significant progresses made on the measuremen-t of charmonium spectrum and their decays, which provide important constraints on phenomenological approaches.The ?(3770) resonance, as the lightest charmonium state lying above the open charm threshold, is generally assigned to be a dominant 13D1 momentum eigenstate with a small 2351 admixture. It has been thought almost entirely to decay to pure DD final states until BES Collaboration observed the first hadronic non-DD decay mod-Searching for other non-DD decays of the ?(3770) has been one of the most interesting topics in the decades. The intermediate meson loop (IML) model predicts keV, both of which have large uncertainties and need con-straints from experimental measurements. Recently, totally 2.92 fb-1 data has been accumulated at (?)s= 3.773 GeV with the BESIII detector at BEPCII, which of-fers us great opportunities to observe the radiative transitions between ?(3770) and ?c(?c(2S)).The decay mode ? is chosen as the first try to search for ?c(?)c(2S)) in ?(3770) radiative transition at BESIII considering the decay rate of ?c(?c(2S)) and background level. No significant excess of signal events above back-ground is observed. We set upper limits at a 90% confidence level for the product branching fractions to be < 5.6 x 106. Combining our re-sult with world-average values of we find the branching at a 90% confidence level. The measured upper limits are within the range of the theoretical predictions but cannot chanllenge them. In this analysis, we also mea-sure the branching fraction of E1 transition ?(3770)-?xc1 using the decay mode and the branching fraction of hadronic decay using the process e+e??ISRJ/?, which give the results (2.33±0.65± 0.43)×10-3 and B{ respectively. The measured branching fraction for ?(3770)??7Xc1 is consistent with the CLEO result in one standard deviation (1?), while the one for at odds with the value of Particle Data Group (PDG) in 1?.Invisible decays of quarkonium states such as J/1?, T, etc., and other mesons provide a window on physics beyond the standard model (SM). This is because the only allowed invisible decay of quarkonium states in the SM is the decay to vv via annihilation into a virtual Z0 boson. The SM predicts ). However, new physics beyond the SM might enhance the branching fraction of J/? invisible decays. One possibility is the decay into light dark matter (LDM) particles mediated by a new, electrically neutral spin-1 gauge boson U, which could significantly increase the invisible decay rate. This motivates the search for invisible decays of the J/?.At BES?, we do so by looking for evidence of the decay of the J/? into unde-tectable final states recoiling against the di-pion system in using a sample of (106.41±0.86) ×106 ?(2S) mesons. We also exclusively reconstruct the events from the process ?(2S) which is used to calculate the ratio of invisible J/? decays to to cancel some common uncertain-ties. After subtracting the background, we find no evidence for J/??invisible and set an upper limit on the ratio at 3.6 x 10-3 at the 90% C.L.. This limit is almost an order of magnitude closer to the SM prediction than the best previous limit from BES?, due to the improvements of statistics and analysis method.