2003 Vol. 27, No. 06
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The continuum one-photon annihilation at ψ(2S) in e+e－ experiment is studied. Such contributions to the measured final states ωπ0 and π+π－ at ψ(2S) mass are estimated by phenomenological models. It is found that these contributions must be taken into account in the determination of branching ratios of ψ(2S)→ωπ0 and ψ(2S)→π+π－, as well as other electromagnetic decay modes. The study reaches the conclusion that in order to obtain the correct branching ratios on these decay modes at BES, at least 10pb－1of data below the ψ(2S) peak is needed.
Maximum likelihood method is adopted to acquire the fitting formula, which could deal with the correlations between different points and different channels in ψ(2S) scan experiment. Sampling technique is employed to avoid the difficulty of too many fitting parameters. The final error of the fitted value is the combination of all kinds of uncertainties. The approach described in this paper could effectively treat the complex correlation problem in experiment data analysis.
By substituting the color separate singlet connections for the color neutral flow connections into JETSET7.4, we select the three-jet events according to DURHAM algorithm in e+e－ annihilation at Z0 pole. We find that the ratio of the special three-jet events defined by constraining the angles between different jets is sensitive to different kinds of color connections. For these special events, different connections lead to significant differences for the charged particle multiplicity of events and properties of the gluon jet. The differences become larger as ycut getting smaller. By taking appropriate ycut, as 0.0005 in this paper, the differences between these two kinds of color connections should be discriminated by experiments.
Based on the bracnhing fractions of J/ψ→VP, γP quoted in PDG-2000, we reexamined the quark content of pseudoscalars. If there is no gluonium content in η and η′, the mixing angle θP=(－19.18±0.91)°. We also present a discussion for DOZI contribution, SU(3) breaking and scalar-meson mixing.
The system of a optical soliton can be described by a singular Lagrangian. To our knowledge, the commutation relations and quantum equations of motion are given by using corresponding principle, it's not satisfactory since the constraints are ignored. In this paper, the commutation relations and quantum equations of motion are derived based on the Dirac theory of constrained systems. The conserved energy, momentum and the number of particles for this system are discussed at the quantum level.
The projectile-like products at 5.3° in the reaction 35MeV/u 36Ar+ 124Sn were inclusively measured with good isotropic identification. With increasing kinetic energy, the average N/Z ratio of the products gradually decreases,approaching to that of the projectile. It is shown from the isospin dependent quantum mechanics(IQMD) that with the increasing of reaction time, the average kinetic energy of the projectile-like products decreases, while the N/Z ratio increases gradually. Moreover, the isotropic composition is obviously dependent on the impact parameter, and the N/Z ratio is becoming smaller with increasing collision centrality.
The Feshbach-Kerman-Koonin multistep compound theory (MSC)of the pre-equilibrium reaction is further improved and perfected. The nucleon is treated as a spin-half particle, target nucleus is allowed to a non-zero spin and the angular momentum coupling is treated rigorously. The expressions of the double-differential cross section and transition matrix elements are obtained in j-j representation. The strength function of doorway state is replaced by optical model absorption, and the escape width is replaced by decay width of Hauser-Feshbach model (HFM)in the r-space where full equilibrium has been established. A unified expression for MSC of pre-equilibrium reaction and HFM of compound nucleus reaction is presented. This formula can integrate MSC and HFM with the optical model and can give self-consistent and uniform description for nuclear reaction. Some typical data are analyzed by using the work mentioned above. The calculated results are reasonable and in good agreement with the experimental data.
The spin assignments for the superdeformed single bands in A≈190 odd nuclei are discussed by use of the method of analysis by synthesis. In this work, the I(I+1) expression is used to fit the experimental energies of γ-transition. In contrast to other procedure, the convergence process of the series expansions is put stress upon whereas how many terms to be taken exactly in the expression does not emphasized. Moreover as well as the method of fitting the physical quantity, the moment of inertia of band heads is also calculated and the method of that systematics is used for the spin assignments. In practice the systematics of the moment of inertia of band heads is more efficient than the method of fitting the physical quantity in the spin assignment. As for a few bands which spin assignment is difficult the deviation from the typical rotational bands must be considered. Finally the results of the spin assignment and the comparison with other literatures are given.
Asymptotic properties of the neutron mean potential are studied using the Skyrme-Hartree-Fock potential and Wood-Saxon potential in the stable nucleus 48Ca and the neutron-rich nucleus 60Ca . We find that the WS potential can reproduce pretty well compared to the SHF potential in the tail part as well as in the surface region for the stable nucleus 48Ca.But for 60Ca ,the WS potential shows a big difference in the tail part from the SHF potential. A corrected Wood-Saxon form is suggested to describe the neutron-halo feature in neutron-rich nuclei. We see that the potential of this form can give a good description of the long tail in 60Ca as well as the surface part.
With the first three terms of Harris formula included and Mottelson's method followed,a new ralation of the parameters of Bohr-Mottelson rotational spectra formula is brought forward. Superdeformed bands of even-even nuclei and normal deformed bands of nuclei in actinide and rare-earth are fitted with four-parameter Bohr-Mottelson rotational spectra formula.The ralations of the parameters A,B,C,D are studied.The result show,for normal deformed bands,the new relation approach the experiment value in the same degree as the relation deduced from ab formula,but for super-deformed bands,the new relation is closer to the experiment than the relation deduced from ab formula.Three-parameter Harris formula may have better convergence than two-parameter Harris formula.
From QGP kinetic equations with collision integrals,by using the realaxation time approximation,we calculate the distribution functions to the second order correction. We obtain the distribution functions for quarks (and anti-quarks) and gluons under the perturbation of the fluctuation of the color field.Then in the high-temperature-low-density area,we discuss the characteristics of the distribution functions,and use them to get the net baryon density and the energy density.
The performance of BESⅡ Barrel Shower Counter (BSC) was carefully studied. Calibration and reconstruction of BSC were improved. Better determination of z coordinate,better resolutions on z coordinate and angle were achieved. A method to determine correct shower developping direction was given.
The luminescence and point defects of pure lead tungstate crystals (PbWO4) and Bismuth (Bi) doping crystal (PbWO4:Bi)grown by modified Bridgman method are studied. It is found that irradiation results in the great change of the transmission and X-ray excited emission after γ-ray irradiation about 4 Mrad dose. The defects in PbWO4 crystal have been studied by means of positron annihilation lifetime and X-ray photoelectron spectra. The results show that Bi dopant suppresses the concentrations of positron capture centers and low-valent oxygen ions.After γ-ray irradiation,in the pure crystal the concentration of lead vacancy (VPb) is decreased and that of low-valent oxygen increased; on the contrary,in Bi dopant crystal the concentrations of positron capture centers increased and that of low-valent oxygen ions suppressed. It is tentatively proposed that Bi3+ dopants would mainly occupy the sites of lead vacancies resulted from Pb volatilization. And irradiation changes the chemical valence of Bi element,which is Bi3+→Bi5+.The Bi5+ will replace the lattice W6+ ions and it will cause some (WO4)2－ replaced by (BiO3+VO)－.
The trimming coils embedded in poles of magnet are applied in the C-dipole prototypes of CSR. They are used to adjust the uniformity of magnetic fields through reducing outside magnetic field and augmenting inside. The impact of trimming currents on the uniformity of field and multipole components is carefully investigated by using the two kinds of magnetic measurements,hall sensor and long coil,respectively. It is proved that the uniformity which is better than ±1.0×10 -3 can be reached easily. At the same time,the quadrupole and sextupole components of fields have decreased to a low level through optimizing the trimming currents,but,unfortunately,the octupole and dodecapole will increase correspondingly. Finally,the two measured and calculated results are compared. There is very small difference between the results of the two measuring methods. However,all of the measured results are alien to the calculated one because of the insufficiency of the TOSCA calculation.
The geometry of the solid target for the accelerator-driven system was optimized. The yield and spectrum of leaked neutrons, and the energy deposition in the target were studied. A target assembly consisting of tungsten diskes and water layers was proposed in the present work. The problem of large energy deposition in soild target was solved without decreasing the leakage neutron production.
A newly manufactured X-band transit-time tube oscillator is introduced. The major advantages of this oscillator include: 1) simple structure, 2) high conversion efficiency, and 3) RF output frequency almost independent of electron beam voltage. On the accelerator sinus-700, its output power's dependences on system parameters are experimentally investigeted. The experiment results are in excellent agreement with the theoretical predicts, and the design specifications of 9.18GHz microwave frequency, 26ns pulse width and 31% conversion efficiency are reached. At higher powers, the pulse shortening develops. It's presumably because of reflected electrons, which will be traped by a strong magnetic filed, and then disturb the ongoing electron's interaction with microwave.
The beam dynamics in micro-pulse electron guns (MPG) is studied using simulation methods in this paper. Based on the working principle of MPGs and the characteristics of its beam dynamics, a multi-particle trace simulation about the three-dimensional movement of the electrons in a MPG cavity is given by a program SEEG (Secondary Electron Emission Gun) written in VC++. The paper includes the principles of simulation and the stability tests of the program SEEG. A specific MPG is simulated using the program SEEG and the simulated beam dynamic results are given.
Tuning and measuring on a 3-meter aluminum RFQ cold model with three resonantly coupled segments is carried out, RF electric field distribution with flatness better than 4 percent is obtained. The reason for the formation of RF electric distribution steps at the location of coupling cells is described, and the relation of the step size and the local resonant frequency difference between the two sides of coupling cell is also given. With this relation, the RF electric field distribution steps at the location of coupling cells can be removed in one tuning operation. The best tuning procedure is finally determined. Following this procedure, the tuning of RFQ with several resonantly coupled segments is easy and fast.
Photoionization cross-sections of Ar under several pressure values are measured in the energy region from 180eV to 270eV by using monochromatic X-ray produced by the 3W1B beamline of Beijing Synchrotron Radiation Facility (BSRF). The experimental result indicates that the photoionization cross-section of Ar is obviously affected by the pressure of Ar in the vicinity of the edge of L-absorption of Ar: the higher the pressure, the smaller the photoionization cross-section.
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