Studies Of X(1840) Line Shape And η’Decays In J/ψ Radiative Decays

In the quark model hadrons consist of two or three quarks. However, the Quantum Chromodynamics (QCD), which is a field theory of strong interaction, predicts the existence of new forms of hadrons, such as glueballs, hybrids and multi-quark states. Searching for new forms of hadrons plays a crucial role to test the QCD theory, and it has been one of the most important physics goals of many experiments in high energy physics. The BESⅢ/BEPCⅡ works in an energy region of 2 to 4.6 GeV, which is designed for τ-charm physics. The J/ψ decays provide an ideal laboratory for hunting the new forms of hadrons and also testing the QCD. Based on the world’s largest sample of J/ψ events, a search for new forms of hadrons and the study of η’ decays are presented.First, based on a sample of 1.31×109 J/ψ events taken at the BESⅢ detector, the existence of X(1840) in J/ψ�'γ3(π+π-) is confirmed. Meanwhile a rapid descend near the pp mass threshold on the 3(π+π-) mass spectrum is observed for the first time. Two different methods are performed to parameterize the 3(π+π-) invariant mass spectrum. The first parameterization is the Flatte formula for describing line shape of the X(1840). A fit to data yields gpp2-/g02= 3.68±0.57(stat.), where gpp2-/g02 represents for the ratio of coupling strength of the pp channel to the sum of coupling strength of all other channels in X(1840) decays; the result shows very strong coupling between the X(1840) and pp final states. The second parameterization is performed with a sum of two coherent Breit-Wigner functions. In this case, the mass, width and the branching ratio of the X(1840) are determined to be: M = 1821.0±5.1±4.9 MeV/c2,Γ = 71.1± 12.0±13.9 MeV, B(J/ψ�'γ/X).B(X�'3(π+π-))= (1.29±0.09±0.22)×10-5 respectively. The other resonance yielding by this fit is found to be very near the pp mass threshold with M = 1877.3 ±3.4±3.0 MeV/c2, Γ= 33.4±7.3±4.5 MeV, B(J/ψ�'γ/X) · B(X�'3(π+π-)) = (0.76±0.05±0.14)× 10-5, the statistical significance of which is determined to be larger than 3σ. Both methods can provide a reasonable description of the 3(π+π-) mass spectrum and show a connection between X (1840) and the pp mass threshold with a significance larger than 3a, which implies the existence of a particle with strong coupling to proton-antiproton.With a sample of 1.31x 109 J/ψ events accumulated at the BESIII detector, the decay dynamics of η’�'γπ+π- is studied using both model-dependent and model-independent approaches. The results show that an extra contribution is needed besides the p(770) and co resonances as well as the interference taking into account between p(770) and ω. By introducing the p(1450) resonance, or the box anomaly, the model can provide a reasonable description of data. Since the tail of/9(1450) has a similar shape as the box anomaly, it is hard to distinguish the extra contribution from them. The determined mass and width of p(770) are consistent with the previous works and the model-dependent branching ratios of η’�'γπ+π- via ρ(1450) (or the box anomaly) are extracted for the first time. The shape of the di-pion invariant spectrum is also parameterized in a model-independent method by assuming the P-wave to be dominating. In contrast to the previous conclusion based on the limited statistics from the Crystal Barrel experiment, our results indicate that both the quadratic term in the expansion of P(s) and the ω contribution are necessary to yield a good description of data. The significance of the co contribution is determined to be larger than 34σ.Based on a sample of 225.3 million J/ψ events accumulated at the BESIII, the decays of η’�'γπ+π-l+l- (l = e, p) are studied via J/ψ�'γη. A clear η’ signal is observed in the π+π-e+e- mass spectrum, and the branching ratio is measured to be B(η’�'π+π-e+e-) = (2.11±0.12±0.14)×10-3, which is in good agreement with theoretical predictions and the previous measurement, but is determined with significantly improved precision. No r/signal is found in the π+π-μ+μ- mass spectrum, and the upper limit is determined to be B(η’�' π+π=μ+μ-) < 2.9 ×10-5 at the 90% confidence level.