2007 Vol. 31, No. 8

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Particle and field theory
Separation of the Beam Associated Sample from Raw Data
WENG Yao, HU Hai-Ming, GUO Yi-Qing, ZHANG Bing-Xin, JIN Yi, HU Jun-Hui, GAO Yuan-Ning
2007, 31(8): 703-707.
The uncertainty of the treatment for the beam associated backgrounds is one of the dominant errors in the previous R measurement at BES/BEPC. A new method is developed to separate the beam associated sample from the raw data, and this sample is used in tuning the parameters of the hadronic generator LUARLW. This improvement can decrease the systematic error of the selection efficiency of hadronic events, and improve the precision of the R value.
Neutral Higgs Effects on Rare Decay B→Xsl+l in the T2HDM
LV Lin-Xia, XIAO Zhen-Jun
2007, 31(8): 708-714.
We calculate the new physics contributions to the branching ratios of the rare decays B→Xsl+l(l=e,μ) induced by neutral Higgs bosons loop diagrams in the top quark two-Higgs-doublet model (T2HDM). From the numerical calculations, we find that (a) the neutral Higgs boson's correction to B→Xsl+l decays interferes constructively with its standard model counterpart, but small in magnitude; (b) the neutral Higgs contributions to the branching ratio of B→Xsl+l decay can be neglected safely if their masses are larger than 100GeV and tanβ≤40.
On the Application of Gluon to Heavy Quarkonium Fragmentation Function
QI Wei, QIAO Cong-Feng, WANG Jian-Xiong
2007, 31(8): 715-718.
We analyze the uncertainties induced by different definitions of the momentum fraction z in the application of gluon to heavy quarkonium fragmentation function. We numerically calculate the initial g→J/ψ fragmentation functions by using the non-covariant definitions of z with finite gluon momentum and find that these fragmentation functions have strong dependence on the gluon momentum k. As |k|→∞, these fragmentation functions approach to the fragmentation function in the light-cone definition. We find that when |k| is small (for instance in the typical energy scale (about 4—20GeV) of the gluon production at the hadron colliders, such as Tevatron and LHC), large uncertainty remains while the in-covariant definitions of z are employed in the application of the fragmentation functions.
Nuclear and ion Physics
Research on Measurement of 182Hf with HI-13 AMS System
QIU Jiu-Zi, JIANG Shan, HE Ming, YIN Xin-Yi, DONG Ke-Jun, GUAN Yong-Jing, WU Shao-Yong
2007, 31(8): 719-723.
182Hf with half-life of about (8.90±0.09) Ma is an extinct radionuclide and can only be produced by a supernova explosion in nature. Therefore 182Hf is an ideal candidate nuclide for the study on possible supernova explosions in the vicinity of the earth within the last 100 million years. In addition, 182Hf is a long-lived radionuclide of particular interest for nuclear engineering. Accurate measurement of ultra-trace 182Hf is very important for reactor design,studies on nuclear cosmo-physics and other fields. With an accelerator mass spectrometry (AMS), it is possible to detect the trace amounts of 182Hf. In this paper, the detection method of 182Hf with HI-13 AMS system at China Institute of Atomic Energy (CIAE) and the chemical procedures to reduce 182W interference are presented. The energy and TOF two-dimension spectra of 182Hf and 183W for blank and a series of standard samples have been obtained, respectively. The 182W contribution to the counts in 182Hf peak was corrected by 183W normalization. The detection sensitivity of this AMS facility for 182Hf/180Hf ratio measurement is about 4.15±10-11 at present.
Effective Masses of Pentaquark Θ+ in Nuclear Matter
GUO Yan-Rui, LI Xi-Guo, ZHONG Xian-Hui, LIU Zi-Yu, JIN Gen-Ming
2007, 31(8): 724-730.
The properties of baryons in nuclear matter are analysed in the relativistic mean-field theory(RMF). It is found that the scalar field σ meson affects the properties of baryon at high density. A density dependent scalar coupling gσN is determined according to the idea of quark-meson coupling model and extended to RMF. It is shown that gσN affects the property of nuclear matter weakly at low density, but strongly at high density. The relation between the scalar density ρS and the nuclear density ρ and the effective mass of the pentaquark Θ+ are studied with the density dependent coupling constant. The density dependent scalar coupling obviously affects the effective masses of baryons in nuclear matter, especially at high density.
Isospin Dependence of Nuclear Charge Radii and Its Microscopic Demonstration
LEI Yi-An, ZENG Jin-Yan
2007, 31(8): 731-735.
The analysis of experimental nuclear charge radii Rc indicates that Rc deviates systematically from the A1/3 law, i.e., Rc/A1/3 gradually decreases with increasing A, whereas Rc/Z1/3 remains almost a constant. This statement is also supported by the analysis of a large amount of experimental nulcear giant monopole resonance energy data Ex∝ R-1. The deviation of nuclear charge radii from the A1/3 law is basically caused by the isospin independence of A1/3 law, and the isospin dependence has been partly included in Z1/3 law. In the frame of nuclear shell model, a microscopic demonstration of the Z1/3 law is given. The difference in the harmonic oscillator potential strength between proton and neutron (ωp and ωn) can be accounted for by the Z1/3 law. Similar to Wigner's nuclear isobaric multiplet mass equation (IMME), a modified Z1/3 law for nuclear charge radii is proposed.
Time Dependence of Elliptic Flow in Ultrarelativistic Au+Au Collisions
FENG Qi-Chun, ZHANG Jing-Bo, HUO Lei, ZHANG Wei-Ning
2007, 31(8): 736-740.
The freeze-out time dependence of the elliptic flow and the transverse radius rT dependence of elliptic flow at different freeze-out time are studied for non-central Au+Au collisions at sNN=200 GeV with the Relativistic Quantum Mocular Dynamics model. We get the results that the elliptic flow decreases with the freeze-out time and the correlation between the elliptic flow and the transverse radius changes with the freeze-out time what could be explained with the pressure gradient. The transverse expansion velocity of particles emitted at the freeze-out time is adopted as a signal of the pressure gradient.
Probinhg the High Density Behavior of the Symmetry Energy by Using Proton Elliptic Flow
ZHANG Fang, ZUO Wei, YONG Gao-Chan
2007, 31(8): 741-744.
Based on the isospin- and momentum-dependent transport model IBUU04, we calculated the reaction of the 132Sn+124Sn systems in semi-central collisions at beam energies of 400/A MeV, 600/A MeV and 800/A MeV by adopting two different density dependent symmetry energies. It was found that the proton differential elliptic flow as a function of transverse momentum is quite sensitive to the density dependence of symmetry energy, especially for the considered beam energy range. Therefore the proton differential elliptic flow may be considered as a robust probe for investigating the high density behavior of symmetry energy in intermediate energy heavy ion collisions.
Detection Technology and Methods
Unbiased χ2 Estimator for Linear Function Fit Involving Correlated Data
MO Xiao-Hu
2007, 31(8): 745-749.
An unbiased factorized chi-square estimator is constructed to deal with the correlated data for linear function fit. The difference between the biased and unbiased chi-square fitting is expounded. In addition, the simplified R-value measurement is quoted to test the conclusion quantitatively.
Optimization of the HIRFL-CSR Cluster Target
CAI Xiao-Hong, SHAO Cao-Jie, LU Rong-Chun, LI Ming-Sheng, RUAN Fang-Fang, ZHAN Wen-Long
2007, 31(8): 750-754.
A new gas delivery system is designed and installed for HIRFL-CSR cluster target. The original blocked nozzle is replaced by a new one with the throat diameter of 0.12mm. New test of hydrogen and argon gases are performed. The stable jets can be obtained for these two operation gases. The attenuation of the jet caused by the collision with residual gas is studied. The maximum achievable H2 target density is 1.75×1013 atoms/cm3 with a target thickness of 6.3×1012 atoms/cm2 for HIRFL-CSR cluster target. The running stability of the cluster source is tested both for hydrogen and argon. The operation parameters for obtaining hydrogen jet are optimized. The results of long time running for H2 and Ar cluster jets look promising. The jet intensity has no essential change during the test for H2 and Ar.
The Application of Fission Fragments Chamber in Direct Measurement of Heavy Λ Hypernucear Lifetime
SONG Yu-Shou, LUO Wei, TANG Li-Guang, HU Bi-Tao
2007, 31(8): 755-759.
In this paper a new method to measure the lifetime of heavy hypernuclei is introduced, and the main device used in the measurement — fission fragment chamber (FFC) — is tested by a 252Cf spontaneous source at Thomas Jefferson National Accelerator Facility (JLab). The chamber has a single-module timing resolution of ~163ps. Based on the timing resolution tested, our computer simulation predicts that the error of the measured lifetime is about 9.6ps.
Temperature Effects of CsI(Tl) Crystal Detector with APD Readout
CHEN Ruo-Fu, FAN Rui-Rui, XU Hu-Shan, ZHAN Wen-Long, LI Song-Lin, XIAO Zhi-Gang, XIAO Guo-Qing, HU Zheng-Guo, HUANG Tian-Heng, ZHANG Xue-Heng, ZHENG Chuan, FU Fen
2007, 31(8): 760-763.
The temperature dependences of the light output of CsI(Tl) crystal grown at IMP and of the gain of the Hamamatsu S8664-1010 avalanche photodiode (APD) have been investigated systematically. The light output of the CsI(Tl) crystal increases with temperature by 0.67%/℃ in the region from -2℃ to 8℃, and by 0.33%/℃ in the region from 8℃ to 25℃, while the gain of the tested APD decreases by -3.68%/℃ (working voltage 400V) on average in the room temperature range. The best energy resolution 5.1% of the CsI(Tl) with APD was obtained for the 662keV γ ray from 137Cs radiation source.
Particle Identification and Its Efficiency for Small Angle GDH Experiment in JLab Hall-A
LV Hai-Jiang, YE Yun-Xiu, YAN Xin-Hu, JIANG Yi, ZHANG Pei, YE Qiu-Jian
2007, 31(8): 764-768.
To obtain a pure electron sample with high statistics, which is necessary for the asymmetry and cross section analysis for the small angle GDH experiment in JLab Hall-A, the information in shower and gas Cerenkov has been used in the particle identification. Due to the dependence of the kinematics, the PID cut and the corresponding efficiency have been optimized for different runs.
A Two-Dimension Beam Dynamics Simulation Code Base on PIC Method
YANG Jian-Jun, ZHANG Tian-Jue, AN Shi-Zhong, JIA Xian-Lu, LIN Yu-Zheng
2007, 31(8): 769-773.
In order to carry out an in-depth study on the negative hydrogen DC beam transport in the axial injection line of CYCIAE-100, a high intensity cyclotron under design at CIAE, the split-operator method is adopted in this paper for macro-particle dynamics simulation. In this method, the Hamiltonian is divided into two parts: external applied field and space-charge field. The former is dealt with single particle tracking and adopts first order approximation; the latter is dealt with PIC method, and FFT technique is used to solve the Poisson equation. Moreover, we developed an object-oriented code of two-dimension macro particle dynamics (CYCPIC2D) using FORTRON 95 language. This code can be applied to the transport line calculation of arbitrarily distributed beam. The simulation result for CYCIAE-100 injection line is presented, and validated by ORBIT and TRACE-3D. It indicates that the space charge effects have significant impact on the injection line, and the results given by three codes are basically accordant with each other. When the beam intensity reaches several ten milliamperes, the two PIC-based codes CYCPIC2D and ORBIT still give consistent results, while the result given by TRACE-3D shows evident difference with the other two.
Study of the Digital LLRF System for STF
GENG Zhe-Qiao, Michizono Shinichiro, Matsumoto Toshihiro
2007, 31(8): 774-777.
STF is a test facility for ILC which is under construction in KEK, Japan. The digital LLRF system is used to control the RF phase and amplitude inside the superconducting cavities. Because there is no real cavity to be controlled, a real time cavity simulator is designed to simulate the cavity response. An FPGA based cavity controller is designed to control the cavities. In the FPGA program, PI feedback and feed forward algorithm are adopted. Measurement shows that both the cavity simulator and the cavity controller work well.
Microbunch Instability in Wigglers
YANG Yu-Feng, ZHU Xiong-Wei
2007, 31(8): 778-782.
We studied the microbunch instability in wigglers induced by coherent synchrotron radiation (CSR) theoretically and numerically for the first time. This instability occurs only at very small energy spread, and reaches maximum when the energy of electrons and the peak value of the magnet field adopt specific values. Results show that the instability may slightly exist in the wiggler of Beijing Free Electron Laser (BFEL), but does not happen at all in the wigglers of the proposed China Test Facility (CTF) for the X-ray free electron laser.
Optimization Study of the 1MeV RFQ at Peking University
LIU Wei, GUO Zhi-Yu, YAN Xue-Qing, LU Yuan-Rong, ZHU Kun, GAO Shu-Li, FANG Jia-Xun, R.A.Jameson, CHEN Jia-Er
2007, 31(8): 783-786.
ISR-1000 will be used as the injector of the SFRFQ, which is under development at Peking University. The possibility to improve its transmission has been investigated. In order to get better transmission, the input beam parameters and the vane voltage have been optimized without changing the structure of the RFQ. In addition, the error study on input beam parameters of ISR-1000 has been carried out. The sensitivity of those parameters has been obtained by simulation.
Calculation of the Beam Loss in the 270° Bending Magnet System of the Medical Accelerator
LI Quan-Feng, KONG Chao-Cheng, GUO Bing-Qi, XING Qing-Zi
2007, 31(8): 787-791.
The transportation process of the electron beam in the 270° bending magnet system of the medical accelerator is studied under the one-order approximation, and the influence of the initial condition to the beam transportation and loss is analyzed for the calculation of the radiation dose. The theory of the beam transportation, combined with the Monte Carlo sampling method is applied. The simulation result shows that the energy spread is the main factor resulted in the beam loss. The data on the position, energy and direction of the lost electrons obtained through the simulation can be supplied as input to deal with the radiation problem. The result gives that the loss rate of the electron beam is 13.5%, and the direction of the main loss is toward the upside of the irradiating head of the accelerator with the radius 1mm, angle spread 5mrad, and energy spread 10% of the initial beam.
Review on the Study of Multi-quark States
2007, 31(8): 792-796.
In this short review, study of multi-quark states is briefly introduced. Theoretical study of four-quark states, pentaquark states and dibaryons is simply reviewed. Experimental signals relevant to multi-quark states are listed.