2003 Vol. 27, No. 1
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The beam collision center of the BEPC has slightly shifted from geometrical origin of the BES detector and the beam bunch of the BEPC also has certain size. For these reasons, to measure Kso lifetime, primary vertex reconstruction must be carried out. After the investigation of di-muon, bhabha and hadron events, the beam collision center for each run is determined by bhabha and di-muon events. For the large branching ratio of and the existence of the resonance of KⅡ0 , this channel is chosen to provide much pure Kso signal. With the aid of M. C. tools at BES Ⅱ , existing software for secondary vertex reconstruction is adjusted and improved. A new method of secondary vertex determination is used and a better position resolution of secondary vertex is obtained. The lifetime of Ks0 is measured with channel and the inclusive Kso mass is investigated with BES Ⅱ 's 50M J/ψ data sample, which give consistent Ks0 lifetime and mass with PDG' s value within error. 1C fit on K0s mass is also studied with M. C. events. The resolution of momentum and energy of 7π+ , π- and K, is improved too.
The scale for visible jets produced in e+e－ Collisions is studied in some details using Monte Carlo method. It is demonstrated, based on the historical fact that the 3-jet events were firstly observed in e+ e- experiments at √S=17—30GeV,and the relative transverse momentum for visible jets is in the region kt,～5—10GeV/c. It is further shown, using a concrete example, that the number of jets in an event could be correctly evaluated only when kt is in this region. The dynamical fluctuations inside jets determined through different values of kt are compared carefully. It turns out that only when kt,～5—10GeV/c the dynamical fluctuations inside jets will possess the best anomalous scaling property. The relation between the scale 5-10GeV/c of visible jets and the scale 1-2GeV of perturbative QCD is discussed.
Using decomposition of the SU(2) gauge field in terms of unit vector field, we have discussed circulation condition of the spin-1/2 Bose-Einstein dendensate. For the two-component Bose-Einstein condensate,the SU/(2) symmetry of the internal states leads to a generalization of Mermin-Ho relation as a topological constrain of the superfluid velocity.
The excited odd qs-coherent state aqs+m|α〉qso and excited even qs-coherent state aqs+m|α〉qseare constructed. The q,s, and m dependences of the antibunching effect are numerically studied. It is shown that for smallr , the excited even qs-coherent state aqs+m|α〉qse exhibits strong antibunching effect but the even qs-coherent state |α〉qse exhibits strong bunching effect; When the q (q≤1) is far from 1,as r2 increase, the second-order qs-correlation function exhibits oscillating phenomenon (i.e. alternates between antibunching effect and bunching effect), whose amplitude and period increase as s and q decrease, but are approximately independent of m; When q→1, the second-order qs-correlation function also exhibits oscillating phenomenon, whose amplitude and period not only increase as 5 decreases but also are dependent on m; In general, the second-order qs -correlation function is more sensitive to s than to q.
Coherent states and the extension to the even and odd coherent states, and further to the eigenstates of the higher power of the annihilation operator are basic and important macroscopic quantum states in quantum field theory. Recently, these investigations have been extended to the aharmonic oscillator and the quantum algebra with q -deformed or qs-deformed commutation relations. In this paper,the orthogonal eigenstates of the higher order of the annihilation operator of the q-deformed aharmonic oscillator are also derived. It is pointed out that these different macroscopic quantum states have similar squeezing properties of higher order amplitude. The reason is found that the orthogonal eigenstates of the higher order of the annihilation operator of the harmonic oscillator, the q-deformed oscillator, the qs -deformed oscillator, the Enharmonic oscillator and the q-deformed anharmonic oscillator all have even and odd structure, which is similar to the simple even and odd coherent states. For other systems like the system with SU(1,1) Lie algebra or q-deformed quantum algebra also have such properties.
The high spin states of 85Zr were populated by using fusion evaporation 60Ni (28Si,2pn)85Zr reaction. The r-r coincidence and DCO ratios were measured with 10 HPGe-BGO detectors at beam energy 102 MeV. A level scheme with 43 levels and 75 r-transitions are proposed. About 25 levels and 36 r-transitions are added to the previous work. The spin is up to 49/2+ for the yrast band. The first and second bank bandings, are observed with configurations vg9/2 π(g/2) and (vg9/2) π(g9/2) . A △I= 1 Ml band built on the 17/2- is conformed. The level structure is compared with its isotones nuclei and discussed.
The cross sections for Pb(n,x)203Hg,W(n,x)l82Ta and W(n,x)183Ta reactions have been measured by the activation method. The neutron fluences were determined by the cross sections of 93Nb (n,2n)92mNb reaction. The neutron energies in the measurements were determined by the cross section ratios of Zr(n,2n)89m+gZr and Nb(n,2n)92mNb reactions.
Within the isospin dependent Extended Brueckner-Hartree-Fock framework, the Hugenholtz-Van Hove theorem in isospin asymmetric nuclear matter has been investigated and discussed for different orders of approximation made according to the truncation levels in the hole-line expansion of mass operator. The neutron and proton Fermi energies have been calculated. It is found that both the rearrangement contributions and renormalized corrections in the hole-line expansions of the neutron and proton mass operators are necessary for getting a satisfactory fulfillment of the Hugenholtz-Van Hove theorem, indicating the importance of ground state correlations to the single particle properties of asymmetric nuclear matter.
Assuming a single-particle 2p structure of 13C, we study proton-13C elastic scattering at the incident energy of 1 GeV in the Glauber multiple scattering theory. A good agreement between theoretical prediction and corresponding experimental data is obtained. The result evidently indicates a possible halo-like neutron skin of 13C.
Base on Brohm's Statistic-Ablation-Abrasion (SAA) model, the modified SAA model was developed via introducing the isospin dependence of nucleon distribution in nucleus and parameterized formulas for nucleon-nucleon cross section in nuclear matter. It can simulate well the isotopic distribution at both high and intermediate energies. By the improvement of computational method, the range of calculation of isotopic distribution can be increased from three order magnitude to eight order magnitude (even higher) . It can reproduce experimental data and predict the isotopic distribution for very far from stability line which is very important from experimental viewpoint.
The possible reasons for the discrepancy between calculation results based on the statistical evaporation model and experimental data of giant dipole resonance of very hot nuclei are discussed. Both of simulations with the standard CASCADE code and the code coupling complex particle emission are carried out. It is shown that the complex particle emission affects the properties of giant dipole resonance of very hot nuclei.
The experimental measurements have provided the evidence that the suppression of fusion cross-section caused by quasi-fission is very important for the synthesis of super-heavy nuclei by heavy ion collisions. The potential energy surface due to the nucleon transfer in the collision process is the driven potential, which governs the nucleon transfer, so that governs the competition between the fusion and quasi-fission. The dinuclear system potential energy surface also gives the information about the optimum projectile-target combination, as well as the optimum excitation energy for the synthesis of super-heavy nuclei by heavy ion collisions.
The transverse flow in heavy ion collisions can be characterized by the azimuthal anisotropy of the final state particles. A clear signature of the azimuthal correlation between directed and elliptic flow is evidenced in the model calculations . It is found that the azimuthal correlation is sensitive to the type of elliptic flow. The collective transverse expansion in coordinate space affects the azimuthal distributions of the final state particles in momentum space and the space-momentum correlation would develop. The study indicates that the behaviour of elliptic flow in different events depends on the evaluation of event-by-event dynamical fluctuations.
Based on the kinetic theory, the distribution function for fermions in quasi-equilibrium QGP, which is perturbed by the fluctuation of the color field, has been obtained. Furthermore, the physical bases that decide the departure factor are analyzed. The characteristics of the departure factor in high-temperature-low-density and low-temperature-high-density are also discussed.
We briefly review the kinetic equations obeyed by classical non-Abelian plasmas. We get analytical effective mass including the effects of temperature and chemical potential when the contributions of both quark and anti-quark are considered. We derive the "Hard Thermal Loop" self-energy by solving these equations after the mass value is given. Our result is completely the same with the one from field theory.
Monte Carlo method is used to simulate the process of avalanching and signal collection of the Multi-gap Resistive Plate Chambers (MRPC) . The result is compared with experimental data to probe the detection efficiency and signal amplitude of MRPC. The effect of different conditions is also discussed.
The two-dimensional position sensitive silicon detector has been tested using Tu a source and ion beams provided by HIRFL + RIBLL. The operation conditions have been studied carefully for best energy resolution, position resolution and position linearity. Various problems are discussed according to some qualitative analysis.
The nonlinear transport of intense pulsed beams is analyzed with the Lie algebraic method in the case of K-V distribution , and the particle trajectories of second order approximation in the 6-D phase space (x,x′,y, y′, τ, pτ) are obtained. The beams could be axial-symmetrical or non-axial-symmetrical in the transverse direction. In the analysis, the effective fields of lens are divided into several small intervals. Each interval is treated as a uniform accelerating field and each dividing point is considered as a thin lens. Let the Lie map act on each uniform accelerating field and thin lens, the nonlinear particle trajectories can be obtained.
A theoretical analysis for energy resolution of Johann monochromator is made, and several estimation formulae corresponding to various geometry conditions are given. Comparing to some other conventional formulae, the formulae given in this paper show a better agreement with SHADOW ray tracing results.
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