https://indico.ihep.ac.cn//event/9242/

I have presented the paper about Electromagnetic Dalitz Decay in which psi(3686) decaying into four leptons and J/psi in the final state. In this paper, the author has observed this type of decay first time. The study of ELectromagnetic Decays has been observed many times in light-quark meson sectors however, the analogous transition in charmonium decays have not yet been studied. BESIII experiment confirms that the contributions from the higher order multipole amplitudes in psi(3686)->gamma chicj are very small and E1 contribution is dominant. Therefore, it is a great interest to measure the EM transition of ψ(3686)-> e+e-χcJ and χcJ-> e+e-J/ψ.The EM Dalitz decays in charmonium transitions, such as ψ(3686)-> e+e-χcJ or χcJ->e+e-J/ψ, have access to the EM transition form factor of these charmonium states. The q^2 dependence of charmonium transition form factors(TFFs) can provide additional information on the interactions between the charmonium states and the electromagnetic field, where q^2 is the square of the invariant mass of the e+e− pair, and serve as a sensitive probe to their internal structures. The q^2-dependent TFF can also serve as a useful probe for exotic hadron structures based on different models. The analysis uses a data sample of 4.479*10^8 ψ(3686) events taken at a centre of mass energy sqrt(s)= 3.686 GeV collected with the BESIII detector. The fit results are shown in Fig. 2 and the corresponding signal yields are summarized in Table I. For the six observed decay modes, the statistical significance of the yields are all larger than 5 standard deviations. Xin has asked the question that how can we measure the yield larger than 5 sigma. I told him that I can be calculated by the ratio of yield and it’s uncertainty. Further in the paper the author has discussed about the systematic uncertainty aand their sources. I have summarized the talk and mentioned that this experimental work will spur new theoretical development on the use of charmonium Dalitz Decays to address questions such as nature of exotic charmonium. Questions: Xin’s Question: why the “q^2-dependent TFF” can be served as a probe for exotic hadron structures based on different models? Answer: EM Dalitz decays in charmonium transitions have access to the EM transition Form Factor(TFF’s). In other words, The transition states have the access to the EM TFF’s. The q^2 dependence of charmonium TFF’s can provide additional information on the interactions between the charmonium state and electromagnetic field, where q^2 is the invariant mass of e+e- pair, and serves as a sensitive probe to their internal structures. Furthermore, the q^2 dependent TFF can possibly distinguish the transition mechanism based on the ccbar scenario and also the other soultions which alter the simple quark model picture. Hence, the author claims that the q^2-dependent TFF can also serve as a useful probe fro exotic hadron structures based on different models.In the future, the intrinsic structure of X(3872) can be well extracted by coparing the experimental measurement of q^2 dependence of TFF with different model calculation. The nature of X(3872), namely, whether it is a compact charmonium, multiquark state with quark clustering, or hadronic molecule can possibly be disentangled by the q^2 dependence of its TFF. Yuhang’s Question: On page3, it says:” The unknown modes are simulated using the LUNDCHARM model.” What’s LUNDCHARM? How to filter out unknown parts from the generated cases or LUNDCHARM can only generate unknown cases. Answer: You have the answer in your second line of the question. Yes, LUNDCHARM is an event generator for J/ψ and ψ(3686) decay.The LUNDCHARM model can generate all the cases which are theoretically known. In the paper, they have only taken the unknown cases from this generator. Suyu’s Question: Her question was about the decay processes? Answer: They are analyzing cascade decay process and both have same final state. In the first manner ψ(3686)-> e+e-χcJ or χcJ->γJ/ψ secondly ψ(3686)-> γχcJ or χcJ->e+e-J/ψ.

Special Topic 61: Kai presented a very interesting paper of N.Cabibbo of “Semileptonic Hyperon Decays and Cabibbo-Kobayashi-Maskawa Unitarity”. He mentioned that it could be a good idea for search for new physics contribution for the estimation of uncertainty condition delta. In table-I the results from V_us analysis using measured g1/f1 values and it is nearly the same values with kaon decays and larger from the previous analysis in somewhat. The larger V_us value from hyperon decays beautifully satisfies the uncertainty constraint.

Kai has introduced the next JC99 paper “First measurement of Form factor”.