1990 Vol. 14, No. S2
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The design and construction of the Barrel Shower Counter (BSC) for the Beijing Spectrometer (BES) are described in detail. The BSC is a 3.85 m long cylinder with an inner diameter of 2.5 m and an outer diameter of 3.4 m, constructed on a 4.23 m long aluminum spool with a diameter of 2.5 m and a thickness of 3 cm. It is composed of 23 layers of lead (0.5 r.l. each as absorber) and 24 layers of self-quenching streamer (SQS) tubes, weighing 40 tons and with a solid angle coverage of 80% of 4π.
Radiation damage effects of several Chinese-made high-Z scintillation crystals have been studied on a 60Co irradiation unit of 100 kCi. Results on small size BGO crystals irradiated by 60Co γ-rays with various doses from 5×103 to 7.5×105 rad are presented. The non-linear decrease of the scintillation light output with the increase of the dose applied and saturation effects have been observed. The spontaneous recovery of the light output can be described by the sum of at least three exponential functions. The radiation damage effects of small size BaF2, CsI(Tl) and ZnWO4 crystals at 5×105 rad were also investigated. Serious damage to BaF2 has been found. Preliminary analyses indicate that this may be attributed to the inclusion of certain critical elements, in the crystal. CsI(Tl) after irradiation does not exhibit strong afterglow or noticeable coloration as were reported in the literature.
Based upon Monte Carlo simulation and particle tracing, the positron source of the BEPC is designed and the predicted performance is compared with the experimental measurement. It shows that they are in good agreement. Important conclusions are drawn from the study presented in this paper:the increase in the electron gun current up to 10 A is beneficial in spite of the deterioration effect on the beam spot size at the target; positron current increases with the bridge coil and solenoid current and the position of matching field peak relative to the target; the existence of two injection phases and their significance; the electrons and positrons from the target do not have to be separated and the R. F. separator is not necessary, etc. The above results are important to the tune-up and operation of the BEPC, and provide a useful reference for the future design of positron accelerators.
On the basis of the field theory at finite temperature, the dependence of π-meson and σ-meson effective masses upon temperatures at nucleon level and one π and one σ exchange potentials are discussed. The dependence of the π and σ effective masses upon temperatures is found to be in good agreement with the results given by the Nambu-Jone-Lasinia model at quark level.
By means of the coherent state effective potential method, we re-examine the Gross-Neveu (GN) model. A "nontrivial" "Autonomous" theory is obtained for any N (N is the number of the fermion fields). When N→∞, the theory is equivalent to that obtained by GN. The dynami symmetry breaking of the "Autonomous" theory will be restored at the critical temperature. The mass of the elementary excitation is temperature dependent, but independent of N.
The ratios of the yields of charmed baryons to mesons in e+e- annihilations have been calculated by using the quark production rule and the quark combination rule. The results vary with energy √ and are in agreement with the available data.
A 1 + 1 dimensional lattice U(1) gauge model is exactly solved. The results show that the lattice gauge model has a correct continuum limit.
In this paper, the structure of the wide resonance peak produced in the J/ψ radioactive decay around 1.7 GeV is studied in terms of the generalized moment analysis, and a method of testing whether there simultaneously exist the Θ/f2(1720) and G(1590) states in the peak is provided. The result shows that G(1590) really exists, and it will be a direct evidence that the G(1590) is a candidate of the 0++ glueball.
Various E1 transition rates for cc states are calculated in a QCD-motivated potential model. Relativistic corrections are found to be substantial. A good agreement between theory and experiment is achieved for the rates of ψ(2S)→YXeJ and XeJ→γψ(1S) (J=0,1,2), but the calculated rates for ψ(3770)→YXeJ are smaller by a factor of 2 than their experimental values obtained by the Mark III Collaboration. The effect of the 23Sl-13D1 mixing may be important and needs to be considered.
Two nonlinear effects in high energy heavy ion collisions-intranuclear cascade and interaction among secondary particles——are discussed. Their influence on the final-state-particle distribution and its target mass dependence are analyzed. Using the hydrodynamic model, the target mass dependence of rapidity distributions is calculated. The results agree well with the existing data.
Considering the intranuclear cascade, a model describing the distribution of the number of grey particles in high energy hadron-nucleus collisions is proposed. An agreement between the model and experimental data is obtained. It seems that the number of grey particles could reasonably be used as a measurement of the number of hadron-nucleon interactions inside the nucleus.
The inclusive momentum distributions of the projectile-like fragments produced in the reactions of 14.7 MeV/u, 19.2 MeV/u 20Ne + 58Ni are compared with the exclusive ones coincident with charged particles, detected in the forward 20 plastic scintillators. The contributions of the fragmentation and transfer processes are decomposed, and the competition between these two processes is studied at different beam energies.
The interacting Boson model and the interacting Boson-Fermion model are applied to nuclei in the rare-earth region in this paper. The Q · Q Hamiltonians are introduced to treat the deformed nuclei in this region. The energy spectra and E2 transitions of W and Os isotopes are calculated and compared with the experimental data.
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