1993 Vol. 17, No. S3
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The application of the dE/dx method for e/π identification of the measurement of the mass of τ heavy lepton by Beijing Spectrometer (BES) operated at Beijing Electron Positron Collider (BEPC) is described. With additional dE/dx information, the efficiency of selecting the eμ events from τ+τ- is increased more than three-fold compared to that with traditional e/π identification by electromagnetic shower measurement alone. This results in not only reduction of the loss of the eμ events in off-line selection, but also in a 75% reduction of the amount of the time needed to run the BES/BEPC for data collection and computer CPU time for data off-line processing for selecting the same number of τ+τ- events.
The GklBa2(Cu1-xFex)3O7-δ system with x=0.005-0.01 and various oxygen concentrations was investigated by 57Fe-Mössbauer spectroscopy in the temperature range 20 K to 300 K. The spectra of the orthorhombic phase were analyzed with four quadrupole doublets. Three of them are attributed to substitutional Cu(l) sites and one (with the smallest quadrupole splitting) to the substitutional Cu(2) site. From an analysis of the temperature dependence of the relative site intensities, different local Debye temperatures for the Cu(l) sites were derived. Highly texturized absorbers were investigated to study the polarization dependence of the four quadrupole doublets. Measurements at the magic angle give evidence for a vibrational anisotropy (Goldanskii-Karyagin effect) of the Cu(l) sites. The Cu(l) site with the largest quadrupole splitting exhibits the lowest Debye temperature and the largest vibrational anisotropy.
The motion of charged particle beams in a beam optical system can be described by means of the transformations of the phase space contours and particle distribution functions. These transformations comprise several groups:the beam transport (BT) group, contour preserving (CP) group, distribution preserving (DP) group, etc. The principal problems of beam optics can be reduced to the following:the determination of the eigen phase space contour of a transformation and the determination of the transformation in which the shape of a phase space contour can be preserved.
Although the Lund model can be used to qualitatively explain enhanced baryon rates in direct γ decays, a quantitative explanation has not been given. With no additional parameters, we analyze γ three-gluon decays in the framework of the "quark production rule" and the "quark combination rule", which were successfully used in explaining e+e-→q →2 jets events, and obtain a good quantitative explanation.
In order to reduce the influence of the geometrical acceptance and improve the precision we introduce the pseudoscalar meson angular distribution of moment HJ(jm, θ). It is more sensitive than the usual projective pseudoscalar meson angular distribution WJ(θ) in determining whether the spin of the ξ(2220) is 2 or 4. We also give some moments required by the moment analysis and helicity amplitude ratios XJ and yJ represented directly by some relations of moments.
The angular distribution for the process of J/ψ→V1 + X, X→γ+ V2, V2→2P or 3P (where V1 and V2 stand for the vector mesons, P is a pseudoscalar meson) are presented. They can be used to determine the spin of the boson resonance X and its parity in some special cases.
With the aid of imaginary-time temperature field theory and fermion mass spectrum derived from Ward-Takahashi identities with composite fields, the vertex correction among fermions and σ meson is calculated beyond the leading order in 1/N expansion in 2+1 dimensional chiral Gross-Neveu model. The behavior of the vertex function with temperature and decoupling phase transition are discussed. The critical temperature of decoupling phase transition arises when the fermion mass and the π meson mass at zero temperature increase; the vertex correction resulting from thermal fluctuation will influence the fermion dynamical mass and cannot be ignored at finite temperature.
The order parameter, Polyakov line <L>, of the U/(l) gauge model on Nσ3×Nτ(Nτ=l) lattice by using the cumulant expansion is calculated to the 5-th order. Emphasis is placed on the behavior of the cumulant expansion in the intermediate coupling region. The necessity of higher order expansion is clarified from the connection between the cumulant expansion and the correlation length. The variational parameter in the n-th order calculation is determined by the requirement that corrections of the n-th order expansion to the zeroth order expansion should vanish. The agreement with the Monte Carlo simulation is obtained not only in the weak and strong coupling regions, but also in the intermediate coupling region expect in the very vicinity of the phase transition point.
In the case of central collisions, the mechanism of fragmentation is studied within the framework of Boltzmann-Uehling-Uhlenbeck theory from lOMeV to 100 MeV for 20Ne+ 20Ne collision system. The exciting energy and the problem about whether complete thermalization be attained have also been discussed.
Based on the Dyson boson expansion and the modified Jancovici-SchifF substitution, a one-one correspondence between the fermion collective pair space and interacting boson space is obtained. It is shown that one can uniquely determine the boson mappings of fermion operators and the IBM Hamiltonian takes a noii-Hermitian form. The fermion matrix elements are directly calculated in the IBM boson space. The rather complicated state projection, which is used to remove the spurious states, can also be performed there.
An n-particle transverse correlation function for analysis collective flow is proposed, which extends the study of n-particle azimuthal correlations and the estimation of collectivity to include the effects of both magnitude and angle for the n-particle transverse momentum vectors. This method is more sensitive to the collectivity of collective flow than the method based on multi-particle azimuthal correlations. Using the new method, n-particle transverse correlations are analyzed for collisions of 1.2 A GeV Ar + KC1 in the Bevalac streamer chamber, and the results have been compared with a Monte Carlo simulation, which show that the collectivity for this experiment is between 85% and 95%.
The heavy-quarkonium nuclear bound states are recalculated by solving the Klein-Gordon equations. We find that the ηc(2980) can be bound in nuclei.
By means of a generalized three-level solvable model, the self-consistent procedure for solving the Hartree-Fock (HF) equation is studied in detail. It is pointed that some attention should be paid to the multiplicity of the solution. Different criteria for choosing a proper solution are considered and discussed. The reason for the sudden jump of the HF solution in some force-parameter (FP) regions, the stability of the HF solution and the FP dependence of the solution are also investigated.
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