2001 Vol. 25, No. 7

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Particle and field theory
BESⅡ Error Matrix Correction on Charged Channel
HONG Tao, LV Feng, ZHANG Chang-Chun, TONG Guo-Liang, SHEN Xiao-Yan, MAO Ze-Pu, LI Wei-Guo, SUN Liang-Feng, BIAN Jian-Guo, WANG Jun, YU Guo-Wei, YUAN Jian-Ming
2001, 25(7): 607-616.
The error matrix correction for charged track parameters of BESⅡ detector is carefully studied. The proper MDC wire spatial resolution (σ=250μm) and Q correction are incorporated into BESⅡ data reconstruction program. The BESⅡ effective material passed through by tracks from interaction point to MDC is taken into account in the kinematics fitting package TELESIS,to correct the multiple scattering and dE/dX energy loss effects. By analyzing the J/ψ→μ+μ data sample,the RUN by RUN error matrix calibration is completed for BESⅡ 24×106 J/ψ events. After these corrections of the error matrix,TELESIS can be applied to BESⅡ J/ψ data analysis with fairly good accuracy.
Calculation of the Vacuum Wave Function for (2+1) Dimensional Lattice QCD
LI Jie-Ming, JIANG Jun-Qin
2001, 25(7): 617-620.
Using the improved lattice Hamiltonian and the truncated eigenvalue equation method,we compute the vacuum wave function of (2+1)-dimensional QCD. The numerical results display good scaling behavior
Color-Octet Contributions in High Energy π-p Collision Process
WANG Xiu-Lian, DUAN Chun-Gui, WANG Hong-Min, HE Ming-Zhong
2001, 25(7): 621-627.
In this paper, using the color-octet mechanism of Q, the cross section of high Energy π-p Collision process is calculated. We found that the color-octet contributions can not be neglected and are even larger than color-singlet contributions at high PT. Compared with the future experiments, the parton distribution functions that we have used and QQ color-octet mechanism can be examined.
Coefficient Algebra of the Minimal Representation of the Elliptic Quantum Group
SHI Kang-Jie, FAN Heng, YUE Rui-Hong, ZHAO Shao-You, HOU Bo-Yu
2001, 25(7): 628-635.
The algebra of the coefficients in the minimal representation of the An-1 quantum group, discussed by Felder and Varchenko, is given in this paper. Those coefficients are associated with the Boltzmann weights of A(1)n-1 interaction-round-a-face model. We show that the algebra satisfies the Yang-Baxter equation. The PBW base for this algebra is also given.
Nuclear and ion Physics
Investigation of Nuclear Deformation in Excited 213Fr
ZHANG Bao-Guo, WANG Su-Fang, DUAN Li-Min, WEN Wan-Xin, JIN Gen-Ming, LI Zu-Yu, HE Zhi-Yong, WANG Hong-Wei, XIAO Zhi-Gang, ZHENG Ji-Wen, WU He-Yu, WEI Zhi-Yong
2001, 25(7): 636-642.
Angular correlations between γ rays and fission fragments were measured for the reaction 16O+197Au at 132MeV. The probability of giant dipole resonance γ rays emission relative to the spin axis of the compound system was extracted by using the correlations,which give direct information about nuclear deformation. Large anisotropy observed in the γ rays energy region of the compound nucleus giant dipole resonance demonstrates unambiguously a deformed shape of the 213Fr compound system at excitation energies of 92MeV. The fission coincidence γ ray spectra were fitted consistently in terms of the statistical γ ray decay of the compound system and excited fission fragments. The giant dipole resonance parameters obtained from the fits were then used to compute the γ ray angular distributions with respect to the compound nucleus spin axis for prolate and oblate shapes. The comparation between the calculation and the experimental results at excitation of 92MeV show that the 213Fr nucleus is in the transition from a collective prolate to a noncollective oblate shape.
Isospin Effect on the Slope Temperature at Backward Angles in the Reactions 30MeV/u 40Ar+112,124Sn
XIAO Zhi-Gang, WU He-Yu, WANG Hong-Wei, LI Zu-Yu, JIN Gen-Ming, DUAN Li-Min, ZHANG Bao-Guo, HU Rong-Jiang, WEI Zhi-Yong, LIU Yong-Ying, WANG Su-Fang, LU Zhao-Hui, ZHU Yong-Tai, ZHU Hai-Dong
2001, 25(7): 643-650.
The coincidence measurements between residues and light particles have been carried out for the reactions 30MeV/u 40Ar+112,124Sn. The times of flight of the residues are measured by PPACs installed concentrically around the beam at forward angle. The spectra of 3He,α and 6He detected at backward angle in coincidence with residues having different average velocities are analyzed with moving source fit. The average excitation energy of hot nuclei is obtained in the incomplete fusion frame. It is shown that the slope temperature extracted from 3He(6He) spectra is higher (lower) in the neutron-rich system 40Ar+ 124Sn than that in the neutron-deficient system 40Ar+112Sn. For α particle. there is almost no difference between the two reaction systems. The possible causality of these systematic behaviors is discussed from the selectivity of the emitting particles along the decay chain of hot nuclei. The calculation of GEMINI can not repsoduce the experimental observations.
Investigation of the Production of Slow Particles in 60 A GeV 16O Induced Nuclear Emulsion Reaction
ZHANG Dong-Hai, SUN Han-Cheng
2001, 25(7): 651-657.
The multiplicity distributions and correlations of grey track producing particles(Ng), black track producing particles(Nb) and heavy track producing particles(Nh) have been studied in 60 A GeV 16O induced nuclear emulsion reaction. The multiplicity distributions of grey particles,black particles and heavy track producing particles can be reproduced by FRITIOF(version 1.7) taking cascade mechanism into account and DTUNUC 2.0 with an incident energy of 200 A GeV. The mean multiplicity of black particles b> increases with the number of grey particle Ng up to 10 and then exhibits a saturation for peripheral,central and mini-bias events;the average values of grey particles g>(heavy track producing particlesh>)inerease with increasing values of black particle Nb(grey particle Ng).
The Effective DBHF Method for Finite Nuclei
LIU Ling, CAO Li-Gang, MA Zhong-Yu
2001, 25(7): 658-667.
A density dependent effective interaction in the relativistic Mean-Field (RMF) theory was adopted to reproduce the Dirac-Brueckner-Hartree-Fock (DBHF) results and applied to study the ground state properties of finite nuclei for both stable and unstable nuclei, especially Ca and Pb isotope chains. The coupling constants of σ and ω mesons are density dependent and parameterized by reproducing the scalar and vector potentials of the DBHF results at each density in the RMF approximation. In this way the RMF approach is equivalent to the relativistic DBHF method, which is usually called the density dependent RMF approach (DDRMF). Rearrangement self energies in the DDRMF were obtained by a variational derivatives of the vertices in the effective Lagrangian. It was found that the rearrangement terms in the DDRMF provide a repulsive potential in the Dirac equation. The single particle energy levels become less bound and the nuclear radius is expanded. In contrast the proper total binding energy was obtained by subtracting the rearrangement energy, which compensates the weak binding of the single particle states. As a result, the total binding energy is slightly increased. The ground state properties of stable nuclei, such as 16O,40Ca,48Ca,90Zr, and 208Pb were studied. An improvement of including rearrangement term and good agreement with the experimental data were obtained. The similar effects were also found in the isotopes of Ca and Pb. It may conclude that the DDRHF is equivalent to the DBHF and an efficient method in the studying of finite nuclear properties. It can be used to describe very well the ground state properties not only stable, but also unstable nuclei without any free parameters.
On Isospin Excitation Energy
LI Wen-Fei, ZHANG Feng-Shou, CHEN Lie-Wen
2001, 25(7): 668-673.
Within the framework of Hartree-Fock theory using the extended Skyrme effective interaction, the isospin excitation energy as a function of relative neutron excess δ was investigated at different temperatures and densities. It was found that the isospin excitation energy decreased with the increment of temperature and/or the decrement of density. We pointed out that the decrement of isospin excitation energy was resulted from the weakening of quantum effect with increment of temperature and/or decrement of density. Meanwhile, the relationship between the isospin excitation energy and the symmetry energy was discussed and found that the symmetry energy was just a part of the isospin excitation energy. With increasing temperature and decreasing density, the contribution of the symmetry energy to the isospin excitation energy becomes more and more important. The isospin excitation energy as a function of relative neutron excess was also investigated using different potential parameters. The result shows that the isospin excitation energy is almost independent of the incompressibility and the effective mass, but strongly depends on the symmetry energy strength coefficient, which indicates that it is possible to extract the symmetry energy of the nuclear equation of state by investigating the isospin excitation energy in experiments.
Effects of the Space Charge Forces and the Beam Halo in a Cyclotron
2001, 25(7): 674-679.
With the space charge forces considered, simulations of the evolution of the beam bunch in the K70 AVF cyclotron, which is an injector of the K540 RIKEN Ring Cyclotron (RRC), are carried out. The result shows that the deformation of the bunch and the formation of beam halo also take place in a cyclotron. But the mechanism of the formation of the beam halo in a cyclotron is different from that in a linear accelerator.
Shunt Impedance and Power of the BEPC DC Separator
DAI Jian-Ping, CHAI Xue-Dong, ZHAO Zhen-Tang
2001, 25(7): 680-683.
During the operation of BEPC, the cable isolation layer near the high voltage connector of the DC separator is often melted, which is probably caused by the power of the resonant modes. This paper presents the measurement of the shunt impedance and the calculation of the power dissipated in the separator and through the connector.
Study of Matching between HIRFL and CSR
TANG Jing-Yu, LI Hao-Hu, YUAN You-Jin
2001, 25(7): 684-688.
HIRFL-CSR Cooler Storage Ring' makes use of existing HIRFL as its pre-accelerator. In order to take the full capability of HIRFL, we have studied in detailed the matching modes between HIRFL and CSR. It is proposed to use two matching modes: direct matching between SFC (HIRFL injector cyclotron) and CSRm (CSR main ring); three-cascade matching of SFC, SSC (HIRFL main cyclotron) and CSRm. With these combinations, better beam transmission efficiency, better beam utilization efficiency of HIRFL-CSR accelerator complex and better operation efficiency of HIRFL can be obtained. In the first case, SSC can be used simultaneously in other purposes, either to accelerate medium energy heavy ions or to accelerate protons combined with another small cyclotron.
Diagnosis of Individual Cell Frequencies in a Coupled Cavity Chain by Genetic Algorithms
NI Yi, TONG De-Chun, LIN Yu-Zheng
2001, 25(7): 689-695.
Genetic algorithms (GAs) is used to diagnose individual call frequencies in a coupled cavity chain with no need of any probe insertion. The cell frequencies and couplings between the cells are determined in terms of the measured pass-band performance. It will simplify the tuning processes and make the tuning of the sealed cavity possible. The solution is cast as an optimization problem and GAs is used as a function optimizer to solve this problem. Moreover, in order to expedite the convergence, nonlinear least squares method is added as one kind of mutation into GAs, which makes GAs converge faster and improves the precision of the solution. The effectiveness of the new technique has been demonstrated through some numerical examples, and the results have also been compared with those of the conventional GAs.
Design Studies of a Photocathode RF Gun for Short-Wavelength FELs
ZHAO Qiang, LI Yong-Gui
2001, 25(7): 696-700.
Low emittance and high intensity electron beams are needed for the high gain, short wavelength FELs. To meet the requirements of the proposed DUV FEL facility in Shanghai, we designed a 1.5-cell, S-band photocathode RF gun using the emittance compensation techniques. Based on the simulation codes of POISSON, SUPERFISH and PARMELA, this design aims at producing a beam of εn,rms=2.3π·mm·mrad, Q=2nC/bunch, Ek=4.8 MeV at the gun exit with the field gradient of 100MV/m on the cathode. In this paper, we present the design considerations and the simulation results.