https://indico.ihep.ac.cn//event/9864/

Gu Shan presented the JC-103 Paper “Evidence of a Resonant Structure in the e + e − → π + D^0D^*− Cross Section between 4.05 and 4.60 GeV”.

The talk had started with the introduction:

The Y(4260) was observed only in hidden-charm processes, while its mass is close to open-charm thresholds, studies of the open-charm production cross section in e+ 𝑒− annihilation will provide important information on its properties.

The production of 𝑒+𝑒− → 𝜋𝐷𝐷bar^* is expected to be strongly enhanced above the nominal D𝐷_1 (2420) threshold and could be a key for understanding existing puzzles with these Y states.

In this Letter, we report improved measurements of the production cross section of 𝑒+𝑒− → 𝜋+𝐷^0𝐷^∗− at center-of-mass energies from 4.05 to 4.60 GeV using data samples taken at 84 energy points with the BESIII detector.

She has shown the event topology 𝑒+𝑒− → 𝜋+𝐷^0𝐷^∗− in which 𝜋+ can be reconstructed and D^0 can be traced with K+𝜋- and D^*- can be inferred from energy-momentum conservation. There will be charge conjugate modes are implied, unless otherwise noted.

She has shown the fitting to the D^*- mass inferred by the invariant mass recoiling against the D^0𝜋+ system, RM(D0𝜋+). Further, calculation of born cross-section has been shown with ISR correction factor and the correction factor from vacuum polarization. Also, dressed cross-section has been shown in the plot(see figure on page-6).

Questions:

Yuhang’s Question: In FIG2,what’s meaning of the phase-space contribution?

Answers: For each energy point, we generate MC samples of the signal process according to phase space (PHSP MC). (In dynamical system theory, a phase space is a space in which all possible states of a system are represented, with each possible state corresponding to one unique point in the phase space. For mechanical systems, the phase space usually consists of all possible values of position and momentum variables. The concept of phase space was developed in the late 19th century by Ludwig Boltzmann, Henri Poincaré, and Willard Gibbs).

Xin’s question: For the paper in equation 2, could you explain what does the “dress cross-section” mean? Answer: 𝜎𝐵𝑜𝑟𝑛 is the observed cross section, when considering the correction factor for vacuum polarization, 𝜎𝐵𝑜𝑟𝑛 ×(1/|1−𝕀|)^2, it is the so called dress crosssection, 𝜎𝑑𝑟𝑒𝑠𝑠 .

My Question: what is R1 and R2 in Fig-2?Can you please explain Fig-2 a little bit? Answer: Two enhancements obtained from the fit result of the cross section.(see page-6 for the plot).

Ryuta’s Question: could you explain about the relationship of those ?

1) Y(4260) without open charm channel decay (==dip) and DD1bar(2420) molecule interpretation

2) observation of open charm channel (𝜋+𝐷0𝐷∗−) with Y(4220)? Answer: We didn’t observe Y(4260), it is just observed in the hiddencharm processes. DD1bar(2420) molecule model is proposed as an interpretation of the Y(4260). We observed the Y(4220) in this paper. She also referred some papers:

Phys. Rev. D 90, 074039 (2014)

Phys. Rev. Lett. 111, 132003 (2013)

Phys. Rev.D 94, 054035 (2016).

Yuzhen has shown the abstract and the motivation for the next JC-104 Paper, “Technology developments and first measurements of Low Gain Avalanche Detectors (LGAD) for high energy physics applications”.