2000 Vol. 24, No. 10
The family events observed with iron emulsion chambers at Mt. Kanbala are analyzed and compared with the simulations by the COSMOS code and CORSIKA code respectively. A detailed study on the production of super-high energy γ-hadron families with energy concentration behavior is carried out. The preliminary conclusions are: 1) the energy concentration behavior of super-high energy γ-hadron families is the external embodiment of high energy central shower clusters contained in the families. 2) the mean lateral spread of these clusters is about 0.37cm. 3) the frequency of this phenomenon appeared under the conditions of R≤10mm and χ10≥90% is (20.5±3.1)%. 4) compared to the COSMOS code based on the phenomenological multicluster model,the simulation by the CORSIKA code that adopts SIBYLL model is closer to the analytical results of experiment.
Based on 7.8×106 J/ψ events collected by BES experiment,J/ψ radiative decay J/ψ→γγV(ρ,φ) have been studied. The η(1430) resonance has been observed in these two channels respectively. Its mass,width and branching ratio are 1431±17MeV,88±28MeV,and Br(J/ψ→γη(1430)) Br(η(1430)→γρ)=(1.1±0.5±0.3)×10－4 from J/ψ→γγρ mode,1424±15MeV,73±58MeV,and Br(J/ψ→γη(1430))Br(η(1430)→γφ)=(2.0±1.0±0.6)×10－4 from J/ψ→γγφ mode.
The Yukawa corrections from the pseudo-Goldstone bosons (PGBs) in the one generation technicolor (OGTC) model to the process γγ→b are calculated. We find the corrections from the PGBs to the cross section γγ→b are more than 10% in the certain parameter values region. The maximum of the relative corrections to the process e+e－→γγ→b may reach －51% in laser back scattering photos mode,and is only －17.9% in beamstrahlung photons mode. The corrections are greatly larger the contributions from the relevant particles in the standard model and the supersymmetric model. It can be considered as a signatures of finding the technicolor at the next-generation high energy photons collision.
A possibility to search for the isoscalar 1－+ exotic state through the J/ψ decay process J/ψ→V+X,X→a2+π at BEPC/BES is discussed in two cases of single state and two-state coupling.The results show that this possibility is existent both in J/ψ radiative decay and hadronic decay processes.
In the frame of color-octet mechanism and according to NRQCD factorization of q production,using three sets of parton distribution function of Pomeron given by L.ALvero et al.,the cross section of J/ψ in γ+p→p+J/ψ+X process is calculated and discussed with the s =200GeV,4GeV
T<10GeV. Our results show that the NRQCD matrix elements had a great influence on cross sections,but a little influence on the ratio of diffractive cross section to inclusive cross section. If the influence is eliminated,the ratio is only related to the flux factor and parton distribution functions of Pomeron.
The vacuum state of (2+1) dimensional SU(2) lattice gauge field theory is investigated. The general expressions of the parameters (μ0 and μ2) of the continuum vacuum wave function are derived.The numerical results which come from the improved Hamiltonian and the truncated eigenvalue equation method display a good scaling behavior in the deep weak coupling region.
The energy spectra of intermediate mass fragments (IMF) emitted in 30 MeV/u 40Ar+115In reaction has been measured. After analyzed the energy spectra of the same kind of IMF emitted at different angles,the dependence of emission mechanism of IMF on the emission angles has been obtained. Assumed that the speed of the moving sources and the Coulomb energies do not change with the emission angles,the moving sources fitting of the measured energy spectra have been completed by changing the intensities and the temperature parameters of the emission sources.The evolution of the portions and intensities of three different emission sources as a function of the emission angles has been discussed.
The energy spectra and angular distributions of products(Z=4-14) emitted in reaction 156.3MeV 28Si+12C were measured by using ΔE-E telescope detectors. Then Lorenz invariant cross sections of the products were presented. The most probable kinetic energy distributions El(θ) in the laboratory system and total kinetic energy Et(Z) in the center of mass system were calculated for the products with Z=4—11,which indicates that these products come mainly from binary process. The complete fusion cross section was deduced to be (980±68)mb for this reaction system. The difference between this value and that extrapolated from the cross section at low energy may attribute mainly to the binary process.
The possible neutron and proton drip line nuclei and their corresponding properties of Pr isotope chain are studied in the framework of the relativistic mean-field(RMF)theory with non-linear meson self-interactions. The pairing effect is treated by BCS method and the isospin dependent pairing strengths have been adopted.The‘blocking’method is used to deal with the last unpaired nucleon and the axially symmetric deformation is assumed.The theoretical results show that the nucleus 185Pr could be determined as the last stable nucleus with respect to the nucleon emission on the neutron rich side from various aspects,while on the proton rich side,it is difficult to determine the proton drip-line nucleus in present studies.The reason is that on the proton rich side the Fermi surface increases faster towards the continuum state than that on the neutron rich side,where the BCS method fails,and the coupling between bound and continuum states should be taken into account.
Effect of deformation on prescission particle emission was studied. The fission delay time extracted from the measured prescission light charged particle multiplicity of fission of light system 111In, produced in 10.6MeV/u 84Kr+27Al collision, is reduced to 5×10－21s from 20×10－21s, if including deformation effect, which indicates that part of the excess of prescission particle emission comes from the deformation effect contribution. The reason is that deformation of the system leads to a decrease of the barriers for proton and α particle emission even larger than the increase of their binding energies.
Isospin effect of fragmentation reaction on isotopic distribution was investigated by a modified statistical abrasion-ablation model. It is shown that the isotopic distribution shifts toward the neutron rich side for neutron rich projectile, but this isospin effect will decrease and disappear at last when (Zproj-Z)/Zproj closes to 0.5 and becomes larger than 0.5 independent of the reaction systems, where Z and Zproj are the atomic numbers of the produced isotop and projectile, respectively. It is pointed out that the disappearance of isospin effect comes mainly from the geometry effect in abrasion stage and the evaporation process later.
Damping of giant resonance in hot nuclei is investigated using time dependent twobody correlation density matrix theory (TDDM) at several finite thermal excitation energies corresponding to temperatures T =0—6MeV. The results are obtained by solving numerically the set of coupled equations of motion for the one body density matrix ρ (11′;t) and the twobody correlation function C2(12,1′2′;t), and compared with the results from different microscopic theoretical approaches. The thermodynamic properties of hot nuclei are also presented. It is shown that the TDDM can describe well the damping of giant resonance and the thermodynamic properties of hot nuclei.
Based on the concept of correlative degree, a new method of high-order collective-flow measurement is constructed in this paper, with which azimuthal correlations, correlations of final state transverse momentum magnitude and transverse correlations can be inspected respectively. Using the new method the contributions of the azimuthal correlations of particles distribution and the correlations of transverse momentum magnitude of final state particles to high-order collective-flow correlations are analyzed respectively with 4π experimental events for 1.2A GeV Ar+BaI2 collisions at the Bevalac stream chamber. Comparing with the correlations of transverse momentum magnitude, the azimuthal correlations of final state particles distribution dominate high-order collective-flow correlations in this experimental samples. The contributions of correlations of transverse momentum magnitude of final state particles not only enhance the strength of the high-order correlations of particle group, but also provide important information for the measurement of the collectivity of collective flow within the more constraint district.
Leptonic decay and radiative transition of ψ′ in medium at finite temperature and density are studied by using different quark antiquark potentials. The behaviour of ψ′ in the medium at finite temperature and density is obtained.
The production of metallic ion beam by means of many methods in high charge state ECR (Electron Cyclotron Resonance) ion source is reviewed. A small evaporation oven with external diameter 8 mm and length 70 mm was tested for metallic ion beam production. The small oven could reach more than 1300℃ with 110W electric power. 140eμA of Ca11+and 70eμA of Ca12+ beams were achieved on the 14.5 GHz ECR at 1MP ion source by using the oven. The Ca11+ beam had been provided to the IMP cyclotron for three weeks with a good stability. In order to obtain intense metallic ion beam, MIVOC (Metallic Ion from VOlatile Compound) method was tested successfully on the 14.5 GHz ECR ion source. 65eμA of Fe10+ by MIVOC method was obtained. During running of the ion source with Ca11+, the oven temperature was not controlled easily by changing the electric power because of extra heating by microwave which was already tested. So a new type of oven was designed in order to avoid this problem. MIVOC method is easy to be performed and beam intensity is high, but it is only suitable for a few metallic elements, on the other hand, the vacuum chamber of the ion source could be seriously contaminated if the ion source runs for a long time.
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