2001 Vol. 25, No. 11
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The well known Monte Carlo simulation package JETSET is developed to simulate the hadronic final states in e+e－ collision with center-of-mass energy Ecm10GeV,but not suitable for few GeV energy region. We develop a Monte Carlo program, LUARLW,which can well simulate two-body up to six-body hadronic final states at BEPC energy region. In LUARLW,the effects of all gluonic emissions are neglected. The LUARLW produces more than 14 distributions,which agree with the BES data very well. This package is used for estimating hadronic events detection efficiencies in the measurements of total cross section of hadron production at BES between 2—5 GeV.
The higher-order squeezing and antibunching effect for the odd and even generalized q-coherent states of the non-harmonic oscillator are investigated. The numerical method is used to study these effects for the two expressions of q-number[χ]. It is shown that the odd and even generalized q-coherent states of the non-harmonic oscillator present higher-order (order of odd number) squeezing effect and antibunching effect respectively,and these optical statistics properties are very different from those of the states of the harmonic oscillator.
Based on the low energy QCD Lagrangian and using the wave functions of [SUSF(6)⊙O(3)]sym.⊙SUc(3) quark model of baryon structure,the strange meson photo production off the proton is studied. Calculations on cross section for γ+p→K++Λ reaction are performed and compared with experimental data. The theoretical predictions are in good agreement with data.
From the Bargmann-Wigner equation in coordinate representation, a convenient form of field equations for arbitrary spin, which are similar to the Rarita-Schwinger equations for arbitrary half integral spin, is derived rigorously. The method used here is to expand the completely symmetric multispinor field with symmetric matrices and a tensor or tensor-spinor field. Meanwhile, the Lagrangian functions for fields with arbitrary integral and half integral spin are given respectively.
Particle particle correlation functions at small correlation angle have been measured for 40Ar+93Nb collision at E 25MeV/u. Based on three body trajectory calculation the emission time scale of light particles has been extracted from correlation function of two particles at small relative momentum. The mean emission time scale decreases with increasing sum of the kinetic energies of the particles in a correlated pair. It decreases from about 500 fm/c for low energy particles to about 50 fm/c for high energy particles. And the extracted emission time scales from larger detection angle are longer than that extracted from the data obtained at small detection angle, which can be explained as the more particles emitted from equilibrated system.
Coincidence measurements between residues and light charged particles (LCPs) have been made for the reactions 30MeV/u 40Ar+112,124Sn. The LCPs were measured by 11 semi-conduct telescopes from very forward angle to backward angle. The times of flight of the residues were measured by PPACs installed concentrically around the beam at forward angle. The excitation energy of the primary hot nuclei was obtained from the velocity of residues in the frame of incomplete fusion model. The single isotope ratios, as function of observing angle and excitation energy have been studied. The ratio of 3He/4He and 6Li/7Li increases with angle while that of 6He/4He and 8Li/7Li decreases. The calculation of statistical theory can not reproduce the curve quantitatively, implying the existence of dynamic effect. Isospin effect of the primary hot nuclei on the single isotopic ratios is demonstrated. However, the temperature extracted from double isotope ratios is target independent.
On the basis of "cone" jet algorithm, a Monte Carlo study of the properties of (mini) jets in high energy hadron hadron collsions is carried out. Using the "jetty frame", in which the momentum of jet is chosen as Z axis, the distributions of physical quantities inside jets multiplicity, pseudorapidity, azimuthal angle and transverse momentum are obtained. The pseudorapidity distribution is asymetric, concentrating in the forward direction, which means that all the particles in the jet are moving forward in the direction of the total momentum of jet. This is further proved by a particle momenta plot in the axial coordinate which shows that the jets look like sharp arrows with small forward pointing feathers at the ends. The transverse momentum distribution for the event sample with respect to the direction of incident hadrons diviates from an exponential distribution considerably, in consistent with the productuon of (mini )jets, while that inside jets with respect to the jet axis is basically an exponential. This means that the production of (mini ) jets is hard process, while the developement of jets is basically soft. These results show that "cone algorithm" is an effective method for the study of hard and semi hard processes in high energy hadron hadron and relativistic heavy ion collisions. It is found through the comparison of the distributions in jetty events and no jet events that Et=2GeV is a more reasonable cut for the "cone algorithm" in finding jets.
The dynamical fluctuations inside jets in the p-p collisions at CERN SppS collider are studied using Monte Carlo method. The event sample is produced using the LUND Monte Carlo generator PYTHIA5.5(JETSET7.3). The jets are identified by "cone" jet algorithm. The vector sum of the momenta of all the particles inside a jet is defined as the axis of this jet. Rapidity y,transverse momentum pt and azimuzal angle φ are defined with respect to this axis. Second order factorial moments are calculated for these variables and the Hurst exponents Hij=lnλ
Hadron and string cascade model (JPCIAE),based on the hypothesis without introducing the quark gluon plasma(QGP),is employed to study the direct photon and π 0 transverse momentum distributions for central 208Pb+208Pb collisions at 158A GeV/c. The theoretical results of transverse momentum distribution for both the direct photon and the π0 particle are lower than the data of WA98 experiment. However,JPCIAE model can ever explain successfully the results of WA80 and WA93 experiments of central S+Au collisions at 200A GeV/c where there is no evidence of direct photon excess. Having considered the results of WA80 and WA93 experiments can be explained but WA98's can't,that might provide a circumstantial evidence for the possible production of QGP in the high energy central Pb+Pb collisions.
An improved Glauber theory for calculalions of the total reaction cross section at low and medium energies is proposed. The quantum effect,Coulomb effect and isospin effect of nucleon-nucleon collision inclnded in the improved Glauber theory are discussed under the assumption of the effective nuclear density distribution. It is found that quantum corrections is very important when the Glauber theory is applied to calculations of the nucleus-nucleus reaction cross. The calculated results obtained with the improved Glauber theory are in agreement with the experimental data in ten percent without any free parameters,which demonstrate the improved Glauber theory to be a pragmatic approach for calculating total nucleus nucleus reaction cross sections in the low and intermediate energy regions.
In this paper a newly developed medium-type pulsed fast neutron detector is proposed. The detector consists of front insulator,n-p converter,absorber,collector and rear insulator. The detection principle is based on the output signal from both recoil-protons of the n-p converter and secondary electrons induced by the recoil protons passing the interface between the absorber and the collector. Because of its detection of fast neutrons in the medium,unlike many trandifional fast neutron detectors which work in the vacuum environment,this detector has obvious advantages. It does not need vacuum environment and high voltage power supply. This makes it to be used easily. By choosing teflon as the absorber and by choosing graphite as the charge collector,the contribution of the secondary electrons to the output signal can be determined experimentally.
In order to study new isotopes and nuclear decay properties in the A>170 mass region, the laser ion source is needed and developed. For on line isotope separator, it is required that the capillary ionization has a speciality of low hot ionization efficiency and high ion extraction efficiency. The principle of the hot capillary ionization was described. The employment of Nb capillary reduces the temperature for forming the plasma potential and inhibitory hot ionization. The ionization tube is made of a Nb capillary of 2.2mm outside diameter, 1.7mm inside diameter and 30mm effective length. The temperature is 1600-2500K when the current is 40-100A. The target chamber is structured by Ta tube of 0.1mm wall thickness and windows of 6μm Ta foil at two ends. Its maximum temperature is 2200K with the current 300A. The test experiment with on-line conditions at isotope separator ISOLAND has been performed.167Yb(T1/2=17.5min) isotope was produced in nuclear reaction 18O(50MeV/u)+natTa→167Yb. In the condition of target chamber temperature 2130K and capillary temperature 2130K, the total efficiency is 0.2%. This target ion source system will be satisfied in laser ion source.
A preliminary design of superconducting section of proton linac for spallation neutron source is made, which includes the design and optimization of the cavity shape and the architecture design of the superconducting section. In addition, the choice of the cell number of the superconducting cavity, the value of the geometric βG, the optimization principles of cavity and the beam dynamic properties are discussed in this paper.
A vertical calibration system with the error of about ±15μm for the newly eight BPMs is described here, which has been developed for the upgrade of the injection system in NSRL phase II project. A data procession to calibrate the BPM and the error calculation methods for fitting of the electric field as well as the calculating result are also presented. A commercial available Bergoz BPM Module, which works on heterodyne receiving with up tp 75dB dynamic range and 1μm resolution, is introduced. With the calibration system and the data procession methods, we have completed the calibration and the inspection of the quality for newly developing eight BPMs.
Time gapped communication commutator is designed for normal communication in strong electromagnetic interference region. There is strong electromagnetic noise in National Synchronization Radiation Lab, which interferences with the normal communication. In order to explore the feasibility of normal communication in strong EMI region, the commutator has been cooperately developed. This article expounds the physics design, the circuit and work process, and spot communication test of the commutator. The spot test result indicates that the communication commutator has the ability of anti interference, and the commutator can normally communicate in the strong EMI region.
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