1996 Vol. 20, No. 2

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Determination of J/ψ Leptonic Branching Fraction Via ψ(2S)→π+πJ/ψ
BES Collaboration
1996, 20(2): 97-106.
Two processes ψ(2S)→π+πJ/ψ,J/ψ→1+1 and J/ψ→anything are carefully studied to get the J/ψ leptonic branching fractions with the ψ(2S)data at BES/BEPC.The results are B(J/ψ→e+e)=(5.90±0.07±0.16)% and B(J/ψ→μ+μ)=(5.96 ±0.08±0.16)%,and Be/Bμ is estimated to be 0.990±0.018±0.024.Assuming Be=Bμ,the leptonic branching fraction of the J/ψ is B(J/ψ→1+1)=(5.93±0.05 ± 0. 16 )%.This result is used to estimate the QCD scale factor ∧(nf/MS) and the strong coupling constant αs.
Preequilibrium Fission
Liu Zuhua, Zhang Huanqiao, Xu Jincheng, Qian Xing, Qiao Yu, Lin Chengjian
1996, 20(2): 107-112.
It is verified experimentally that the heavy-ion-induced fusionfission reactions are entrance-channel mass asymmetry dependent.This dependence means that in some cases,the fused composite systems havenot forgot the history of it's formation.Based on the experimental observations,we have put forward a preequilibrium fission model.In framework of this model,we have successfully explained the anomalous fragment anisotropies from fusion-fission at near-andsub-barrier energies.
First Experimental Determination of Half-Life for New Nuclide 65Se
Huang Wenxue, Xu Xiaoji, Hu Zhiqiang, Ma Ruichang
1996, 20(2): 113-118.
By using experimental data obtained from the measurement of beta-delayed proton decay of 65Se produced in 40Ca(28Si,3n)reaction,the absolute detection efficiency of particle telescope for rotating radioactive source was imitatively calcu-lated.The half-life of 65Se was thus accurately determined to be 9.6-4.1+5.3 ms.The β-delayed proton energy of 65Se was 3.70±0.08MeV.The partial decay scheme of 65Se β-delayed proton decay was revised and proposed.
Calculation of Cross-Section and Distribution of Number of Wounded Nucleons in High Energy Hadron-Nucleus Inelastic Collision
Ren Jianglong, Ding Linkai
1996, 20(2): 119-123.
The inelastic cross-section and the distribution of the number of wounded nucleons in proton-Air collision have significant influence on the development of EAS caused by superhigh energy cosmic rays.Based on the data of pp crosssection from accelerator experiments,the inelastic cross-section and the distribution of the number of wounded nucleons in proton-Air collision have been calculated at superhigh energy region.
Phase Structure of U(1) Lattice Gauge Theory by Variational Study with Independent Plaquette Effective Action
Zhao Peiying, Wu Jimin
1996, 20(2): 124-130.
The average plaquette energy Ep of U(1) Lattice gauge theory in 3 dimensions with an independent plaquette effective action is calculated using the variational cumulant expansion.The E-β curve is continuous,which shows that U(1) theory has only one confine phase.Our result is consistent with Monte Carlo data.
Constrained Correlation Dynamics of QED in Canonical Form(Ⅱ)Equal Time Limit and Two-Body Correlation Dynamics
Guo Hua, Wang Shunjin
1996, 20(2): 131-137.
The equations of motion for multi-time correlation Green's functions are transformed into those for equal-time correlation Green's functions,which include the equations of motion for electron's and photon's density matrices as well as vertex functions.In two-body correlation truncation approximation,we present the explicit expressions for the equations of motion,Gauss law and Ward identities explicitly.
String Tension of Cosmic Strings
Yang Kongqing
1996, 20(2): 138-141.
Based on the thermodynamic model of ideal gas of cosmic strings,the string tension is calculated by the saddle point approximation and the expression of string tension is obtained.
ππ Bose-Einstein Correlation at AGS Energies
Feng Zhonghan, Sa Benhao, Wang Ruihong
1996, 20(2): 142-147.
The study of Bose-Einstein correlations between two identical particles offers a powerful probe to the space-time evolution of ultrarelativistic nucleus collisions.We calculate the correlation function of ππ due to the four space-time and four-momentum distributions of π-at freeze-out in hadronic cascade simulation of 28Si(14.6 A GeV/c)+Au reactions.The correlation function calculated by Fourier transformation method,the correlation function resulted from fullcalculation and the corresponding experimental correlation function agree each other very well.The above freeze-out configuration of π is also used to calculate the root mean square length of π source.These lengths are compared with the conventional fitted radius parameters of source.
Ground-State Properties of the Doubly-Magic Nucleus 100Sn
Wen Wanxin, Jin Genming, Zhong Jiquan
1996, 20(2): 148-152.
The groud state properties of the doubly-magic nucleus 100Sn are calculated with the Skyrme-Hatree-Fock method.There may be a proton skin in the 100Sn nucleus due to the Coulomb repulsion.
Color Screeing and Dissociation of Heavy Quarkonium
Liu Bo, Dong Yubing
1996, 20(2): 153-158.
The non-relativistic potential models with color screening are employed to discuss the binding and deconfinement of heavy quarkonium.By means of the two kinds of parametrized potentials in a thermal environment,the screened lengths r are calculated.The results show that the screened lengths rcD depend on the potential behavior in the thermal environment.
20Ne+12C System and the Double-Alpha Transfer effect for a Deep Optical Potential
Gao Chengqun, Yang Baosheng, Zhou Quanhua
1996, 20(2): 159-164.
In this paper,the basic features exhibited by 20Ne+12C system are analyzed and the excitation functions and the angular distributions of the 20Ne+12C elastic scattering are well reproduced on the basis of the nuclear molecular orbital theory.The results show that the double-alpha transfer effect for a deep optical potential is responsible for the above difference in the elastic scattering excitation functions between these two systems.
Theoretical Analysis of an Uqp(u2) Model for Ground-State Bands in Even-Even Nuclei
Zhang Xinming, Zhou Huanqiang
1996, 20(2): 165-174.
The validity of an Uqp(u2)model for the nuclear rotational spectrum is systematically analysed by investigating the Mallmann plots and fitting the experimental data for the even-even rare-earth and actinide nuclei.The results show that the theoretical values obtained from the Uqp(u2) model are in a good accordance with the experimental findings.Thus the Uqp(u2) model has some advantages over the SUq(2)model as far as energy levels are concerned. Further more,a relationship between the parameters of deformations and the nuclear softness is also established.
Study of the Effect of Polarized Sea Quark Pairs on the Spin-Dependent Structures of Nucleon
Dong Yubing
1996, 20(2): 175-181.
The various polarized sea quark pairs are examined.The effects of the sea quark pairs and anti-symmetry between the quarks on the spin-dependent structures of proton and neutron are studied.
A Microscopic Two-Parameter Nuclear Model and Its Application to the Yrast Lines of Actinide Nuclei
Wu Lianao, Ding Huiming, Jing Xiaogong
1996, 20(2): 182-184.
A two-parameter model based on the microscopic fermion dynamical symmetry model is proposed. In terms of the numerical calculation,it is shown that this model can fit the data of the yrast lines of nuclei in the actinide region in very high precision.
Structure Properties of Light Nuclei(Ⅰ)Structure of Li Isotopes
Gu Jinnan, Dai Lianrong, Zhang Changhua
1996, 20(2): 185-192.
The structure properties of Li isotopes are investigated in the framework of large-basis shell model.0hω calculation can reproduce the structure of 6,7Li, but for some states of 8,9 Li far from β-stability line the effect of(0+2)hω excitation should be taken into account for reproducing the experiment at data.For drip line nuclei,enlarging model space or changing the interaction can not reproduce the exotic properties of nucleus 11Li.The exotic properties of some states of nuclei 6—8Li are also briefly discussed.