1990 Vol. 14, No. 3
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The spin-parity analysis of the J/ψ radiative decay products into two pseudoscalars usually uses the angular distribution calculated by the helicity amplitude formalism.This paper investigated the sensitivity of this method and pointed out the followings; 1) there really exists some insensitive area; 2).unfortunately,θ(1720) falls into the insensitive area of 2+-0+ distinction; so the spin of θ(1720) has not been finally established yet; 3).according to the Mark-3 data,for the newly observed very narrow peak ξ(2230),the spin 0+ assignment can be ruled out.
A 6×6BGO array as a prototype of precise fully active electromagnetic calorimeter has been constructed.It consists of 36 Chinese-made BGO crystals,each being 20mm by 20mm in cross section and 200mm in depth,equipped with photomultiplier readout.To obtain linearity over a wide dynamic range,both the anode signal and a dynode signal were digitized.The array has been tested with monochromatic photons produced via (p,γ) reactions at the IHEP Van de Graaff accelerator in the energy range up to 21MeV.The response for photons has shown to the linear in this energy range.The FWHM energy resolution obtained follows a E－1/2 dependence and is superior to that of BGO arrays reported in the literature.
Through Monte Carlo method major factors of the system error in LEP/L3 Luminosity measurement and methods to reduce them are discussed.
We calculate the vacuum expectation values of 6-link SU(2) Wilson loop by using cumulant expansion and Monte Carlo simulation respectively.Their results are consistent.
On the basis of the field theory at finite temperature,the temperature dependences of effective masses of π and σ meson at the nucleon level are discussed.The character change of nucleon-nucleon interaction at low temperature T(T≤200MeV) are also investigated.The temperature dependences of effective masses of π and σ meson are in good agreemet with the results obtained from the Nambu-Jonal-Lasinio model at the 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 dynamical symmetry of the autonomous phase will be restored at the critical temperature.The mass of the elementary excitation is N independent but temperature dependent.
In this paper,we discussed the vacuum gap of Dirac particle in the interior of a atomic nucleus and of a hadron.Results of the calculating showed that the vacuum gap is as a potential well,whether in de Sitter metric for the case of strong gravity,or in Reissner-Nordstrom metric for the case of yukawa field.
In this paper,we discuss two non-linear effects in high energy heavy ion collisions,intranuclear cascade and interaction between the secondaries.Their influence on the distributions of final state particles,especially on the target mass dependence of these distributions is analysed.Using hydrodynamical model,we calculated the distributions and compared their target mass dependence with existing data.
Collective state space truncation causes a difference between particle and hole representations.By taking the midshell 120Xe as an example,the problem as well as the dependence of the difference on parameters are studied within the framework of microscopic approach based on boson expansion and the MJS substitution.The phase transition in the energy spectrum structure from vibrational mode to γ——unstable mode for Xe isotopes is also studied.
The inclusive α-particles ade measured with different kinds of telescopes.The energy spectra,angular distribution,the contour plot of d2σ/dEdΩ in the E-Θ plane and of d2σ/PCdEdΩ in velocity plane are obtained.The α-particles coming from the evaporation of compound nucleus are distinguished from the ones of direct mechanism.With a calculation of Exciton of Exciton Model,the contributions from the preequilibrium and equilibrium α-emission are determined respectively.A small contribution comes from other reaction mechanisms.
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.
The systematics of (n,2n) and (n,3n) cross sections has been studied by means of the evaporation model including the preequilibrium emission.A set of the empirical parameters have been extracted on the bases of analysing and fitting the measured data.The (n,2n) and (n,3n) cross sections of some nuclei have been predicted,and good agreement with the measured data have been obtained.
The nucleon densities ρq of 40Ca and 208Pb determined by finite temperature self-consistent semiclassical calculation are utilized together with nuclear matter approach and local density approximation to evaluate the nucleon-nucleus optical potentials at finite temperature.The self-consistency and the temperature effect have been better taken care of by the present approach.
The expansion dynamical process of a hot nuclear system for energetic heavy ion collision has been calculated and discussed in the frame of the Vlasov equation.It shows that the compression effects are more effective than the thermal excitation for the fragmentation process.
A(1+1)-dimensional lattice U(1) gauge model is solved exactly and the result shows that this model has correct continuum limit.
In this paper by using the generalized moment analysis we have studied the structure of the wide resonance peak at about 1.7GeV produced in J/ψ radiative decay.It provides a method to test whether there exist the θf2(1720) and the G(1590) states simultaneously in the peak.If the G(1590) exists indeed it is a direct check for G(1590) as the 0++ glueball candidate.
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