2000 Vol. 24, No. 6
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Monte Carlo simulations of extensive air shower at the “knee” region are carried out by use of four kinds interactive models according to the condition of Tibet Yangbajing ASγ hybrid experiment.The characters of shower for different interactive models are analysed,and the parameters closely related with primary particle mass are given. The BP artificial neural network(ANN)is used to select the proton events from the simulation results,and the relation between the abilith of primary particle identification and interactive models is studied. The results show that the primary proton events can be effectively identified by ANN methed from simulation data of different interactive models with similar identification capabilities.
A lot of data has been accumulated with Tibet Ⅱand HD AS array operated successfully since October of 1995 and 1996,respectivley. The preliminary results of searching for steady TeV gamma ray emissions from Crab Nebula with these data were presented in this paper. Analysis shows that the accumulative excess events of steady 3TeV gamma ray emissions from Crab Nebula was increasing stably and the statistical significance reached 3.2σ, whereas no statistical significant evidence of steady 10TeV and 30TeV gamma ray emissions was found.
Using a recently developed Monte Carlo effective Hamiltonian method,we study the low energy physics of 1+1 dimensional quantum mechanical system V(x)=μ2x2+λx4(here μ2<0,λ>0),which is similar to Higgs potential in the standard model of unified electroweak theory.Good results of the spectra,wavefunctions and thermodynamical observables are obtained.It shows that the new Monte Carlo Hamiltonian method has potential application to systems with many degrees of freedom and lattice gauge theory.
The Leznov-Saveliev algebraic analysis method and Drinfeld -Sokolov construction are applied to the supersymmetric case. In this approach, we obtained the solution of the osp(1｜4)Toda model on the base of the Lie super algebra osp(1｜4)and its highest weight by introducing chiral vectors. Therefore, we generalized this method to two rank case.
The coupling cluster method is improved to calculate μ0,μ2 of vacuum wave function in 2+1-D SU(2)lattice gauge theory.The calculated results of μ0,μ2 show better scaling behaviors than the results obtained by original method at weak coupling region.
According to Dirac's idea of the space-like consistency conditions,we define the space-like wave functions through introducing the space-like factor,which is equivalent to Bethe-Salpeter wave function in physical content. The space-like form of Bethe-Salpeter equation of both bound state and scatter state are derived in terms of the universal rearranging technology of interaction kernel. Moreover, they are extended to many particles case. We also obtain the normalization condition of the space-like function for bound state and the solution of non-homogeneous term in the space-like form of Bethe-Salpeter equation for scatter state. Consequently the formalism of the relativistic space-like equation is finally built.
Based on perturbative expansion,the contributions to quantum Wilson loop from three-connection field Green functions and from the lowest-order graviton self-energy are calculated respectively.The results show there exists excitation with localized curvature in Einstein gravity when the contributions of three-graviton vertex are considered.
In the reaction of 33.4MeV/u 17N on a target 9Be,the measured neutron spectra at different angles exhibit a complex pattern and vary regularly as a function of the detected angle. The detected neutrons probably come from the three origins:nucleon-nucleon collisions between the projectile and target,break-up of 17N and statistical evaporations from the hot nuclei. By analyzing the measured neutron angular distribution and calculating with QMD and GEMINI for the reaction concerned, 4.49,0.44 and 5.5barns were obtained for neutron emission cross sections due to the three origins mentioned above,respectively.
We study an additional effect of energy loss of the projectile nucleons in unclear Drell-Yan process. With consideration of EMC effect and the energy loss effect,we predict the DY radio on the parton evolution model.An better prediction is given.
The effect of the absorption of pion mesons in relativistic asymmetrical heavy-ion collisions on pion-source parameter is studied with two-pion interferometry at small relative momentum. The relations between the source parameters are obtained when the pion absorption is considered or not. Comparison with the experimental measurements of relativistic asymmetrical central heavy-ion collisions 1.8A GeV Ar+Pb is made.
The features of thermodynamics and particle emission during the disassembly of 129Xe are investigated as functions of temperature and freeze-out density in the framework of the lattice gas model. The calculation shows different temperature dependence of physical observables at different freeze-out density. In this case, the critical temperature at the phase transition depends strongly on the freeze-out density. However, a unique critical excitation energy is revealed in different freeze-out densities when the excitation energy is used as a variable instead of temperature. Moreover, the different behavior of particle emission with temperature stemming from different ρf vanishes when excitation energy replaces temperature. It indicates that the excitation energy can be seen as a basic and scalable quantity to control nuclear disassembly.
With in the frameworu of the three-dimensional Vlasov equation,the dynamical evolution of highly compressed nuclei with high thermal excitation energy has been discussed. The distributions of particles in the space are uniform, while in the momentum space are Woods-Saxon distribution. The effects of initial conditions, temperature parameter and density, on the hot decay are great. The effect of the density on the hot decay is more important than the temperature parameter. For the same initial condition,the hot nuclei is more likely to decay in the hard potential than in the soft potential.
Transition energies, incremental alignments of angular momentum, dynamic moments of inertia of triaxial superdeformed bands in rare earth nuclei have been examined systematically. It is found that the incremental alignments are nearly constant and their dynamic moments of inertia are quite similar. Therefore these triaxial superdeformed bands in rare—earth nuclei are identical bands.
In studying the properties of nuclear higher-spin states, not only is the K-mixture needed to be taken into account, but also the Coriolis interaction (the cranking term) should be introduced. The cranking term breaks the time reversal symmetry, and the projection of the single-particle angular momentum on the intrinsic symmetric axis is no longer a good quantum number. This makes the theoretical calculation somewhat complicated. However, considering some intrinsic symmetry in a nucleus, it is not very difficult to apply the angular momentum projection technique to the PNC wave functions including the cranking components (the cranked PNC wave functions). In this paper the fundamental expressions for calculating the nuclear energy spectra and the electromagnetic properties are deduced and evaluated in theory, consequently the feasibility of actualizing the present scheme is made clear.
Large Hadron Collider operation will produce high radiation background, lead tungstatecrystal is selected as scintillator of the CMS electromagnetic calorimeter To reach the pricision requirement of the energy measurement, strict requirement of the radiation hardness to PWO is needed. In this paper, we present a method for evaluating the radiation hardness and measuremen. results for several full size (23 cm length) lead tungstate crystals under Co60 γ-ray side irradiating, investgating the light yield loss and its longitudinal uniformity.
The nonlinear resonance, chaos and halo formation in space charge dominated beams have been studied. The results for the range of the nonlinear resonance versus space charge effects, and the space charge thresholds of halo formation excited by nonlinear resonance are derived. Some numerical results are also given.
A variational method is presented for computations of both monopole mode and dipole mode rf quantities in metal disk-loaded waveguides. It allows for rounding of edge of a disk hole without any approximation in shape treatment. Good agreement has been found between computed and experimental results. It has higher accuracy than those of some existing simulation programs, hence provides a good tool to calculate wakefield of the tapered disc-loaded waveguides in next generation linear colliders.
In order to calculate the electron trajectory of 200kV self-shielded electron accelerator, the electric field is calculated with a TRAJ program. In this program, following electron track mash points one by one, the electron beam trajectories are calculated. Knowing the effect of grid voltage on electron optics and gaining grid voltage focusing effect in the various energy grades, we have gained scientific basis for adjusting grid voltage, and also accumulated a wealth of experience for designing self-shielded electron accelerator or electroncurtain in future.
Self-calibration experiment of silicon photodiodes in the soft X-ray spectral region of synchrotron radiation (50—2000eV) is carried out. Because of elimination of “dead region” and adoption of very thin SiO2 layer as window of the silicon photodiode, a simple model can be used to analyze the process. Based on parameters measured by experiment, the quantum efficiency of the silicon photodiode is calculated, and the flux of incident synchrotron radiation is also obtained.
A systematic theory of the appropriate spin operators for the relativistic states is developed. This paper discusses it in particle case, i.e., the quantum mechanics problem. For a massive relativistic particle with arbitrary nonzero spin, the spin operator should be replaced with the relativistic one. In the frame of irreducible representation of Poincaré group, this spin operator, which is named as moving spin and applied to all the canonical states of the particle, is constructed. Further discussion on the concept of moving spin in the quantum field theory will be followed.
We apply the shell-model wave functions of 76Ge to calculate the nuclear matrix elements and the half-life of the 2νββ decay of 76Ge. Our result is comparable to the recent observed 2νββ decay half-life of 76Ge. Furthermore it provides the upper limit of the effective neutrino mass is about 0.4eV with the recent experimental data of the 0νββ decay half-life.
Absolute measurement of branching fractions of purely leptonic decay, semi-leptonic decay and φπ+ decay of the Ds meson at a c.m. energy of 4.03 GeV were completed from the BES experiment at the BEPC electron-positron collider. The method by using combined confidence level for pion and kaon separation, the Ds single and double tagging technology, and the maximum likelihood functions in the estimate of the Ds branching fractions are described in details. Discussion and comments on these physics results are made. Prospect for improved measurement of Ds physics in future is also given.
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