1990 Vol. 14, No. S3
Display Method: |
Using a silica aerogel sample filled with oxygen gas as a variable energy positronium source, the effect of the positronium motion in oxygen has been investigated with a time selecting energy spectrometer. The positronium state conversion in an inelastic collision between the fast positronium atom and oxygen molecule has been verified and the conversion cross sections are measured as 2.1×10-17 cm2 and 6.6×10-18 cm2 respectively at the kinetic energies of positronium near two thresholds. For the slow positronium, the conversion cross section due to the exchange of electrons in the elastic collision is found to be proportional to 1/√v, where v is the mean velocity of positronium. This process would provide a clean para-positronium source for other precise experiments.
The analysis of the data from the heavy ion experiments at SPS of CERN and at BNL indicates a strong dependence on the nuclear collision geometry. From this we develop a stochastic method to generate such a geometry by using a computer with the property that the known nuclear charge distributions, the hadronic interaction cross sections and the two nucleon correlations are accounted for in one stable framework.
The first measurement results of the characteristics of the synchrotron radiation spot from the photon beam line 4W1A, such as the size, intensity, energy spectrum and position stability are reported in this paper. The results are quite consistent with the theoretical predictions.
In this paper, we present the design and construction of the luminosity monitor of BES, its main features of the detectors and the functions of the read-out circuits and data acquisition system. In October of 1988,-the luminosity monitor provided the first colliding luminosity of Beijing Electron-Positron Collider (BEPC), and the initial luminosity was 5×1028/cm2·s. During the later colliding experimental operations, the luminosity monitor also provided the colliding luminosities, which were in agreement with those calculated with the operation parameters of the BEPC.
A (1 + 1)-dimensional lattice U(1) gauge model with fermion species doubling is solved exactly. The results show that doubling exists for meson states composed of fermions and antifermions. Furthermore we prove that Susskind fermion scheme can avoid the doubling of meson states.
The possibility of the glueball explanation for the ξ(2230) is discussed in this paper. The ratios of the helicity amplitudes are calculated. It shows that the ξ(2230) cannot be a pure S-wave (or D-wave) 2++ glueball, but it can be a D-wave 4++ glueball.
In this paper the helicity formalism of the angular distribution for processes e+e-→J/ψ→V + X, V→P1P2 and e+e-→J/ψ→V + X.X→P4P5 is given. It provides a theoretical formula for the e+e- experimental data analysis.
For the general cases where the adiabatic conditions are broken, we use the path-integration to derive a topological action related to the Berry's phase and the corresponding effective Hamiltonian, and thereby obtain the probability amplitude of the non-adiabatic transition under the first-order approximation. These discussions manifest the universality of existence of the Berry's phase and induced gauge structure. As an example, the dynamics of induced monopole associated with Bitter-Dubbers experiment is discussed.
The mixing mechanism of the three axial-vector mesons f1(1285), f1(1530) and E/f1(1420) is discussed. The results show that the main component of the E/f1(1420) is the glueball. On this basis we calculate the ratio of the helicity amplitudes and expect an experimental test for this result
The effect of the multi-pion correlations on two pion interferometry in a multi-pion event is studied. A new general two-pion interferometry method is developed, taking into consideration the effect of the multi-pion correlations. The data for 1.8 A GeV Ar + Pb central collisions at the Bevalac streamer chamber are analyzed using this new method.
The mechanism of the one-body dissipation and the influence of quantum effects on the dissipation are studied by use of a Monte Carlo simulation method. The disappearance of quantum effects with increasing amplitude or frequency of the collective oscillation is demonstrated. Finally, the wall formula with quantum effect is given analytically within a certain approximation.
The excitation functions for the 55Mn(α,n)58m,gCo, 55Mn(α,2n)57Co and 55Mn(α,α' n)54Mn reactions are measured by the activation method and stacked-foil technique for energies ranging from 10.4 to 26.5 MeV. The experimental results are compared with the theoretical calculation using the exciton model. It shows that the preequilibrium emission reaction mechanism is present in these reactions.
The variation of nuclear deformations with Z, N is studied with a two-level model with charge independent nucleon-nucleon interactions. Results obtained agree fairly well with the observed ones.
In this article, a modified statistical model is successfully used to describe the disassembly of the hot composite nucleus created in intermediate energy heavy ion collisions (12C (15--45 MeV/A) + 63Cu). The computed dependence of mass distribution of fragments on the incident energy are consistent with experimental data.
- A SCOAP3 participating journal - free Open Access publication for qualifying articles
- Average 24 days to first decision
- Fast-track publication for selected articles
- Subscriptions at over 3000 institutions worldwide
- Free English editing on all accepted articles
- The 2023 Chinese New Year-Office closure
- 2022 National holiday- office closure
- The 2022 summer holiday-Office closure
- Impact factor of Chinese Physics C is 2.944 in 2021
- The 2022 Labor Day Holiday-Office closure