2007 Vol. 31, No. 11

Particle and field theory
Non-leptonic Weak Interaction with Quark Matter in Magnetic Field
ZHOU Xia, ZHENG Xiao-Ping
2007, 31(11): 1003-1009.
We investigate the non-leptonic weak interaction in magnetic field and discuss the improvement of the previous method to analytically work out the rate for weak field case. Our result easily goes over to the field-free limit. Then we calculate the reaction rate in strong magnetic field where the charged particles are confined to the lowest Landau level. A strong magnetic field strongly suppress the rate, which will be foreseen to affect viscous dynamics in SQM. We also derive a few approximation formulae under given conditions that can be conveniently applied.
Probing Top Quark Polarization Effects in Topcolor-Assisted Technicolor Model
GU Qin-Zhong, JIANG Feng-Chun, WANG Xue-Lei, YANG Hua
2007, 31(11): 1010-1015.
We study the polarization effects of the top-quark on the tt production cross sections at hadron colliders in the topcolor-assisted technicolor model. The MRS set A′ parton distributions and the helicity projection operators methods are used in the calculation. It is shown that the polarization effects of the top quark are too small to produce enough identified signals at the Tevatron while they can be large enough to be detected at the LHC with reasonable values of the parameters. The polarization effects at the LHC can reach 16%, therefore, they provide feasible tests of the topcolor-assisted technicolor model.
particle and nuclear astrophysics and cosmology
Accelerated Direct Demodulation Imaging Method
SHEN Zong-Jun, ZHOU Jian-Feng
2007, 31(11): 1016-1021.
The most popular iteration method used in Direct Demodulation Method (DD) is Richardson-Lucy (RL) Iteration. The formula of RL iteration can be rewritten in matrix form. There are two matrix multiplications which contain the main computation cost. They can be transformed into convolution if the system is shift-invariant. As is well known, convolution can be computed by Fast Fourier Transform much faster than computed directly. This paper introduces the details of the above procedure, which is called accelerated direct demodulation method (ADD), and applies the procedure to image restorations of Hard X-ray Modulation Telescope data. This paper also compares the computation cost between the original DD and ADD.
Nuclear and ion Physics
Monte-Carlo Simulation and Study of Sideward Flow for 238U238U Collisions at CSR Energy Area
WU Ke-Jun, LIU Feng
2007, 31(11): 1022-1026.
The ART(a Relativistic Transport) Model is applied for studying the UU collisions at a beam kinetic energy about 0.52GeV/nucleon. We discuss the time evolution and the centrality dependence for sideward flow of nucleons and pions at two extreme orientation UU collisions. It is found that the collective (side) flow is developed in the high density region and has a saturation in the expansion phase, so it is a sensitive probe for the reaction dynamics in the high density region. A distinct transition from pion flow to antiflow, which is relative to nucleons flow, occurs at the impact parameters of about 8fm and 2fm in tip-tip and body-body UU collisions, respectively. The pion flow is a result of the competition between the collective flow of baryon resonances and the shadowing of spectators through rescatterings and reabsorptions.
Exact Bound Solution of the Klein-Gordon Equation and the Dirac Equation with Rosen-MorseⅡ Potential
ZHANG Ai-Ping, QIANG Wen-Chao
2007, 31(11): 1027-1031.
In this paper, the relativistic Rosen-Morse II potential is investigated by solving the Klein-Gordon and the Dirac equations with equal attractive scalar s(r) and repulsive vector v(r) potentials. The exact energy equations of the bound state are obtained by the method of supersymmetric and shape invariance. Finally, a kind of special potential about Rosen-MorseⅡ potential is discussed.
Study on Charge Form Factors of the Exotic Nuclei 6,8He
WANG Zai-Jun, REN Zhong-Zhou
2007, 31(11): 1032-1039.
Charge radius and charge form factors of different charge density distributions for 6,8He are calculated with the relativistic Eikonal approximation. Detailed comparisons and discussions are presented. It is found that the charge form factors curves of 6,8He are much lower than the experimental ones of 4He. This is, in principle, consistent with the experimental fact. Whereas detailed comparison among the charge form factors which correspond to different charge distributions show significant deviations. This indicates that the effects of the correlations between the halo neutrons and the α-core in 6,8He with different charge density distributions are quite different. This result would provide a useful reference for the possible experiments on the next-generation electron-nucleus collider and for the tests of different theoretical models for the exotic nuclei 6,8He.
Initial-State Nuclear Effects in High Energy p-A Drell-Yan Process
WANG Hong-Min, SUN Xian-Jing, HOU Zhao-Yu
2007, 31(11): 1040-1044.
Nuclear shadowing and energy loss effects are two important initial-state nuclear effects in hadron-nucleus collisions. In this paper, by means of the nuclear parton distributions extracted only from lepton deep-inelastic scattering experimental data, the energy loss effect in Drell-Yan dimuon production process is studied in the color string model. By a χ2 analysis of the experimental data given by FNAL E772 and E866, we found the rate of quark energy loss per unit path length: -dE/dz=2.06GeV/fm, which is almost the same as the result expected by the model -dE/dz≈2GeV/fm. The calculated results are compared with the E772 and E866 data. It is shown that the theoretical results considered the energy loss effect are in good agreement with the experimental data.
Detection Technology and Methods
Simulation of Micromegas Detector by Garfield Program
ZHANG Xiao-Dong, CHEN Xu-Tao, ZHANG Yi, YANG He-Run, XU Hu-Shan, DUAN Li-Min, LI Chun-Yan, LI Zu-Yu
2007, 31(11): 1045-1049.
In this paper, a batch file which describes the detailed structure and the corresponding physical process of Micro-Mesh Gaseous Structure (Micromegas) detector, the macro commands and the control structures based on the Garfield program has been developed. And using the Garfield program controlled by this batch file, the detector's gain and spatial resolution have been investigated under different conditions. These results obtained by the simulation program not only exhibit the influences of the mesh and drift voltage, the mixture gas proportion, the distance between the mesh cathode and the printed circuit board readout anode, and the Lines Per Inch of the mesh cathode on the gain and spatial resolution of the detector, but also are very important to optimize the design, shorten the experimental period, and save cost during the detector development. Additionally, they also indicate that the Garfield program is a powerful tool for the Micromegas detector design and optimization.
Muon Identification Using the Efficiencies Ratio Method at BESⅡ
GUO Yun-Jun, HE Kang-Lin
2007, 31(11): 1050-1055.
The momentum and polar angle depended position resolution and hit efficiency in each layer of BES(Ⅱ) muon detector are calibrated by using cosmic ray and hadron samples. Based on the calibration results, the efficiencies ratio function is constructed to separate μ/π effectively and applied in physics analysis.
Performance Study of Monitored Drift Tube Chambers with Cosmic Rays
XIE Wan, OUYANG Qun, XIE Yi-Gang, ZHENG Shu-Cheng, HAN Hong-Guang, CHENG Shao-Chen, YANG Yi
2007, 31(11): 1056-1061.
The performances of monitored drift tube chambers for the ATLAS experiment are studied with cosmic rays. The main features of the chamber and the test facilities are described briefly. The criteria and test procedures for the BEE chambers are presented, including the dark current, the noise level, the drift time spectra, the charge distribution and the relative efficiency. The results are within the specifications required by ATLAS.
A Digital Control Scheme of Power Supply System for RCS/CSNS
HU Wei, ZHANG Jing, QI Xin
2007, 31(11): 1062-1066.
A 1.6GeV proton rapid cycle synchrotron (RCS) was designed in the Chinese Spallation Neutron Source (CSNS) Project. The magnet power supply system of the synchrotron drives nine sets of independent 25Hz White Circuit. The output currents of the nine sets of magnet power supply are the DC-biased AC source. The currents (magnetic fields) must meet the requirements of the phase and amplitude accuracy during the accelerator repetition cycle. Because of the advantages of the digital control technique such as reliability, temperature drift rejection, and high integration and so on, it has been adopted more and more widely in the equipment design. To achieve the rigorous goals such as stability and THD (Total Harmonic Distortion) in the RCS/CSNS magnet power supply system, a digital control scheme will be implemented which will be presented in this paper.
Studies on the Beam Orbit and Energy Instabilities at the BEPCⅡ Linac
WANG Shu-Hong, PEI Guo-Xi, LIU Wei-Bin, CHEN Yan-Wei, YE Qiang, GENG Zhe-Qiao
2007, 31(11): 1067-1070.
During the commissioning and early operation of the upgraded BEPCⅡ injector linac, some beam instabilities were appeared, and have been studied by both experimental and analytical ways. This paper describes the observed beam orbit instabilities, beam energy jitter, and the beam emittance jitter. The ways to cure these instabilities are also presented.
Synchrotron radiation,applications of nuclear techniquees,etc
A Measurement of the Residual Radioactivity with NaI Survey Meter and Its MC Simulation
WANG Qing-Bin, Kazuyoshi Masumoto, Hideo Hirayama, Tokushi Shibata
2007, 31(11): 1071-1075.
The present study shows how Monte Carlo method using EGS4 code can be useful for evaluating the residual radioactivity induced in shielding concrete of accelerator facilities. By using EGS4 code, the response of NaI survey meter concerning the shielding concrete block radius and thickness are calculated. It is found that the surface dose rate is saturated when the shielding concrete radius and thickness reach 40cm and 30cm respectively. Under the above-mentioned conditions, the surface dose rates at position north-8 and south-9 of SF cyclotron in University of Tokyo, are investigated, and compared with the experimental results obtained by NaI survey meter. It is shown that the calculation results are in good agreement with the experiments. In addition, the conversion factor of the surface dose rate to urface residual radioactivity is obtained to be 0.90(Bq·g-1)·(μSv·h-1)-1 for 60Co and 1.26(Bq·g-1)·(μSv·h-1)-1 for 152Eu. By using this conversion factor, we can easily evaluate the radioactivity induced in shielding concrete of accelerator facilities from the experimental results of NaI survey meter.
Material Discrimination by High-Energy X-Ray Dual-Energy Imaging
WANG Xue-Wu, LI Jian-Min, KANG Ke-Jun, TANG Chuan-Xiang, ZHANG Li, CHEN Zhi-Qiang, LI Yuan-Jing, ZHONG Hua-Qiang
2007, 31(11): 1076-1081.
Material discrimination by high-energy (1—10MeV) X-ray dual-energy imaging is investigated in this paper, and an approximately linear model is also proposed. The sensitivity of material discrimination is defined to evaluate the effect of material discrimination. The energy ranges of dual-energy X-ray are optimized by analyzing the X-ray attenuation coefficients after the X-ray penetrate the materials. The sensitivity of material discrimination can be improved by modulating the X-ray energy spectrum with filters. A prototype emitting alternating dual-energy X-ray with 9MeV {\&} 6MeV boundary energies is designed. It can present us the tinctorial images with the material discrimination information. Finally, the experimental results we made agree with the theoretical simulation.
Impurity Entanglement in Spin-1 Heisenberg XX Chain
TIAN Dong-Ping, QIN Meng, TAO Ying-Juan, HU Ming-Liang
2007, 31(11): 1082-1085.
We investigate the impurity entanglement of the ground states and the thermal states at finite temperature for a three-qutrit system of the Heisenberg XX model in the presence of a uniform magnetic field. As a measure of the entanglement, negativity of the state is analyzed in detail as a function of the impurity parameter, temperature and magnetic fields. Magnetic fields are mainly to reduce entanglement. Impurity parameter plays an important role in enhancing the entanglement and improving the critical temperature. We can use them to control entanglement.
Bell Inequalities in High Energy Physics
DING Yi-Bing, LI Jun-Li, QIAO Cong-Feng
2007, 31(11): 1086-1097.
We review in this paper the research status on testing the completeness of Quantum mechanics in High Energy Physics, especially on the Bell Inequalities. We briefly introduce the basic idea of Einstein, Podolsky, and Rosen paradox and the results obtained in photon experiments. In the content of testing the Bell inequalities in high energy physics, the early attempts of using spin correlations in particle decays and later on the mixing of neutral mesons used to form the quasi-spin entangled states are covered. The related experimental results in K0 and B0 systems are presented and discussed. We introduce the new scheme, which is based on the non-maximally entangled state and proposed to implement in φ factory, in testing the Local Hidden Variable Theory. And, we also discuss about the possibility of realising it to the tau charm factory.