The charmonium spectroscopy is of great importance to understand the quantum chromo-dynamic (QCD) theory in perturbative and non-perturbative calculation. The charmonium states below the threshold are well measured, and all these measured states are in good agreement with the theoretical predications of relativistic potential model . However, it is still desirable to investigate the decay properties of these charmonium states. With the high statistics collected for and decays, the first observations or more precise results could be achieved. In this proceeding, the study of and decay to and , improved measurements of , observation of and evidence of , and Dalitz decay to and Dalitz decay to are presented.
The BESIII experiment is operated at the Beijing electron positron collider II (BEPCII) with a peak luminosity of at a center-of-mass energy of 3773 MeV. The BESIII experiment aims to study the multiple-purpose physics in the region based the world's largest charmonium data sample at on-threshold production. A detailed description of the detector can be found in Ref. .
2. The study of and decay to and 
The study of and (denoted as ) decays plays an important role in the test of perturbative QCD (pQCD) calculation. Since the discovery of puzzle which violates the rule, more decay channels are required to further investigate the rule and give information for the development of the future theories.
In this analysis, the branching fractions (BFs) of decay to and are measured with the improved precision based on 1.3 billion and 448 million decays. Both baryon and anti-baryon are tagged by their subsequent decay products. The left panel of Fig. figlamesults shows the distributions of invariant masses of ( ) and ( ) for the decay to and , respectively. The production yields are extracted from the fits to these distributions. The polar angle distributions of baryons in the reference frame can be interpreted as , and they are measured in the right panel of Fig. figlamesults. The fitted values and the measured BFs are listed in Table. tablamres. Note that the value for decay is negative, which is contradictory with the existing theories. The possible explanation for this negative value could be the re-scattering effect  of baryon and anti-baryon in the final states. The rule is observed to be violated since the ratios and are calculated to be ( )% and ( )%, respectively.
3. Improved measurements of 
The electro-magnetic (EM) decay is an important decay mode since the decay is very sensitive to the inner structure of the charmonium state. Based on the data set of 106 M decays collected in the year 2009, the precision on the BF of decay is improved. This improvement is quite necessary in the determination of BFs of decays.
In this analysis, the inclusive decays of where represents all the possible final states are used to determine the BF of the decay . To constrain the signal shape, a clear spectrum from , decays to two or four charged particles is used. Figure figchicjesults shows the reconstructed spectrum for the inclusive and exclusive decays, respectively. Simultaneous fit is used to extract the BF of the decay . The five peaks from left to right in the left panel of Fig. figchicjesults correspond to the decay , , , and and to . The BFs of are determined to be ( )%, ( )% and ( )%, respectively.
4. Observation of and evidence of 
The knowledge on the decay is quite limited since only two decay modes are observed before this study, the radiative decay with a BF of about 50% and the hadronic decay with a BF of about 2%. Search for more decay modes are desirable to understand the properties of the particle.
Based on the data sample of 448 M decays, we present the first observation and the evidence for the radiative decay of and , respectively. The particle in the decay channel is reconstructed from the decay , and , while the particle in the decay channel is reconstructed from the decay and . Figure figgetapresults shows the distributions of invariant masses of ( ) and ( ), respectively. Production yields of the decay and are extracted from the fits to these mass distributions. The BFs of the decay and are calculated to be and with a statistical significance of and , respectively. With these two values, the ratio between the BF of and is calculated to be %, from where the mixing angle can be extracted to test the SU(3) flavor symmetry.
5. Dalitz decay to and Dalitz decay to 
The investigation of EM Dalitz transition plays an essential role in the understanding of the internal structure of hadrons and the interaction between the photons and hadrons. Such transition has not been observed in the charmonium decays before this analysis. The Dalitz decay of and can have access to the EM transition form factor (TFF) of these charmonium states by studying the square of invariance mass of pair ( ) dependence.
Based on the data sample of 448 M decays, we present the first observation of the Dalitz decay of and , where the in the former and latter decay channel is reconstructed by and , , respectively. Figure figepemresults shows the distributions of invariant masses of ( ) and ( ), respectively. The BFs are measured to be , , and , , , respectively. Figure figcmp_polar shows the consistency of distribution between the data and Monte Carlo (MC) simulation, where MC simulated sample is generated according to the model based on the assumption of a point-like meson described in Ref. .