2003 Vol. 27, No. 04
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Based on 4-prong events sample of J/ψ decay and the ψ′ data sample, a method is developed to determine J/ψ total number of two data sets which were taken from November 1999 to May 2001 at BESⅡ. The results are (27.00±1.48)×106 and (30.70±1.62)×106,respectively.
Large Nc approximation is adopted in popular e+e－ event generators where the production probability of singlet chain states is 100% and that of color separate states is 0. In the real world Nc=3, we investigate the origin and character of color and kinematics aspects in interference terms. We find that the production probability of color singlet chain states decreases from 83%, 77% to 67%, 58% for qq+2g and qq+3g system respectively after considering the interference terms. Especially, the production probability of color separate states increases to twice of that without interference terms for qq+2g. Hence when n is larger, we can expect that the production probability of singlet chain states will be far less than 1 and that of color separate states will significantly increase when n is larger.
The existence of the new class of hadronic states, glueball, hybrid mesons and hybrid baryons, is one of the important prediction of the QCD. It is an excited and attractive research preject to search for and identify these non-qq meson and non-qqq baryon states. The theoretical expectations on the mass spectrum of hybrid baryons have been carried out in the bag model, QCD sum rules and flux tube model. We might expect that J/ψ hadronic decay processes are the good place to study hybrid baryons. The J/ψ decay process J/ψ→p+X,X→Δ+π, where p and Δ are the antiproton and Δ baryon with spin parity (3/2)+, respectively, are studied in terms of the angular distribution and the generalized moment analysis methods. Precise angular distribution and moment representation of baryon resonance (including the hybrid baryon) X with spin parity (1/2)±,(3/2)±,and (5/2)± are obtained. They can be used to identify the spin of the baryon resonance state X.
A new off-shell decomposition of SU(2) gauge field without any gauge fixing is proposed. This decomposition yields, for an appropriate gauge-fixing, a Skyrme-Faddeev-like Wilsonian action and confirms the presence of high-order derivatives of a color-unit-vector at the classical level. The ′t Hooft′s conjecture that "monopole" dynamics of infrared Yang-Mills theory is projection independent is also independently demonstrated.
An analysis on the characteristics of lateral distributions of the shower particles in high energy family events with visible energies 100TeV-400TeV observed in lead emulsion chambers at Mt. Kanbala (5500m a.s.l.)is done. The experimental results are compared with those of the corresponding Monte Carlo simulation. The code CORSIKA with QGSJET as the hadronic interaction model is applied in the simulation.It shows that the lateral distributions of shower particles in the simulated family events are basically in agreement with experimental data and the whole distribution tendency of the rate of energy concentration for simulation is basically consistent with experimental data.
We apply the parametric model to fit the surface abundances of three lead rich stars (HD187861, HD196944 and HD224959) without adopting any specific stellar model. It shows that the calculated result can fit the observed data well whether the reaction branchings are taken into account or not. Besides, by the comparison of the model parameters of the three lead rich stars with those of two very metal poor stars (LP625 44 and LP706 7), we find out that the average neutron exposure of the former is larger than that of the latter, but the dredge up extent is smaller. We come to the conclusion that the parametric model is significant of constraints on the stellar model, though it is very simple.
The β-‘waiting point’nucleus 93Pd has been produced via 58Ni(40Ca,3n2p) reaction. A helium-jet fast tape transport system was used in combination with p-γ coincidence measurement to identify the β-delayed proton precursor 93 Pd, whose half-life has been measured to be 1.3±0.2s. The measured energy spectrum of β-delayed protons and relative branching ratios to the final states in the daughter nucleus 92Ru are fitted by a revised statistic model calculation, and then the ground state spin of 93Pd are assigned to be 9/2. Meanwhile, a nuclear energy-potential-surface (EPS) calculation is performed by using the Woods-Saxon Strutinsky method. The calculated result supports the ground state spin and parity of 9/2+ assignment.
High-spin states in odd-odd nuclei of 176,178Ir and 182Au have been studied experimentally using heavy-ion- induced fusion-evaporation reactions and standard in-beam γ-ray spectroscopic techniques. Rotational bands built on the πi13/2 νi13/2 configuration have been observed. In addition, on the basis of level spacing systematics, spin assignments have been proposed for the πi13/2 νi13/2 band in 184 Au,which was reported without spin assignments in previous study. It is pointed out that the πi13/2 νi13/2 bands in 176,178Ir and 182,184Au present a low-spin signature inversion. In the theoretical framework of 2-quasiparticle plus rotor model with p- n residual interaction, the signature inversion phenomenon in the πi13/2 νi13/2 bands has been discussed qualitatively. Theoretical investigations have been performed for the πh9/2 νi13/2 and πi13/2 νi13/2 bands using the cranked shell model. It is found that the signature inversions in both configurations can be well reproduced using the pairing and deformation self-consistent cranked Wood-Saxon calculations.
The track structure of low energy electrons (with minimum energy of 1eV) in water as a media has keen simulated with Monte Carlo method, taking into account inelastic processes such as ionization, excitation, attachment and auto ionization caused by super excitation, and the yield and distribution of some free radicals. The local energy deposit entities: spur, blob and short-track are obtained in any individual track yielded by our program, and radial dose distribution and range as statistical characteristics of 10,000 tracks are also presented. The role of low energy electrons in track structures is analyzed by contrasting with the characteristics of track structures with 1 and 30eV as cutoff energy.
The pseudospin symmetry and its approximation in real nuclei are discussed. When the sum of the vector and scalar potentials is a constant, there will be an exact pseudospin degeneracy and even the usual intruder orbits will have degenerate partners. For real nuclei, the pseudospin symmetry is approximate, and the partners of the usual intruder orbits will disappear. The reason behind this is the contribution of the pseudo spin orbit potential.
Taking medium effects into account, we calculate the bulk viscosity of strange quark matter in high temperature approximation using a consistent thermodynamics method in quasi particle description. We find that medium effects have great influence to the bulk viscosity of strange quark matter, which leads to the result that two flavor superconductivity (2SC) is not excluded by pulsar data, unlike Madsen's result.
The properties of the spin polarized isospin symmetric nuclear matter and neutron matter as well as their equations of state are investigated by employing the Skyrme effective interaction with four sets of parameters SKM*, SⅢ, SLy230a and SLy230b. Whichever Skyrme parameter is used, the ferromagnetic phase transitions are predicted in both the isospin symmetric nuclear matter and neutron matter. Above the critical density, the polarized matter becomes more stable than the unpolarized one. Consequently such a phase transition is one of the possible explanations of the strong magnetic field in neutron stars. In addition the magnetic susceptibility χ is also evaluated and the ratio χ/χF is obtained as a function of the density. The existence of an infinite discontinuity confirms the occurrence of a ferromagnetic phase transition once more.
The electromagnetic field in nuclear Fermi gas and nuclei has been studied. Because in the nuclear Fermi gas the expectation value of the electric charge density operator is not zero, different from that in vacuum, the U(1) local gauge symmetry of electric charge is spontaneously broken in the nuclear Fermi gas, and consequently, the photon gains an effective mass. Perturbation calculation of the photon self-energy shows that the effective mass of photon is about 5 42MeV in the symmetric nuclear Fermi gas at the saturation density ρ0=0.16fm－3 and about 2.0MeV at the surface of 238U. Furthermore, it is concluded that it is just the two body decay of a massive photon that causes the discovery of sharp lines of electron positron pairs in low energy 238U+232Th heavy ion collisions experiments.
In nuclear decay process, internal conversion electron emission and electron capture leave vacancies in atomic shells. The vacancies in atomic shells give rise to rearrangements in the shells which are accompanied by the emission of X-ray and the ejection of Auger electrons. The energies of X-ray and Auger electron can be calculated on the basis of atomic electron binding energies in different atomic shells. The intensities of X-ray and Auger electron can be also calculated from vacancy number, X-ray fluorescence yield and vacancy transfer coefficient of different atomic shells. The calculation methods of energies and absolute intensities of X-ray and Auger electron arising from nuclear decay are introduced briefly. The calculation codes and flow chart are presented. The application is also given by using some nuclear decays as an example.
A new mixing event method is developed in the analysis of relativistic heavy ion collision experiments with a relatively complicated background by using RQMD (Relativistic Quantum Molecular Dynamics) as input data sample. The proposed method is then applied to the study of invariant mass distribution of Δ++ resonance as an example. A new iterative algorithm is also proven by providing the invariant mass spectra of Δ++'s using different algorithms for the combinatorial background subtraction.
A photon detector is composed of CeF3 (Cerium Fluoride) scintiplator and high current photomultipler tube (PMT). The experiment results indicate that the sensitivity of this detector is about 0.6 and 0.1 with respect to that of usual plastic scintillator ST 401, for 60Co γ and pulse DT neutron radiation, respectively. The biggest linear current of this detector is above 1.5 A, dark current is lower than 10nA. This kind of detectors is gamma pulse radiation detectors insensitive to neutron radiation with large dynamic range.
In the BEPC electron positron storage ring, the bunch length and its lengthening are quite important characters. It determines the efficiency of getting physical events and the luminosities achievable, and it plays a key role in the upgrade of BEPC. Because of advantages of precision and visualisation, streak camera is commonly used to measure the beam length in accelerators. In this paper we describe the operation principle, the features and the basic system configuration of the streak camera. The systematic and random errors in the measurement are analysed. Some typical results of measurement in recent years are presented.
Axial field produced by an axially magnetized permanent ring was studied. For two permanent magnet rings, if they are magnetized in the same direction, a nearly uniform axial field can be produced; if they are magnetized in opposite direction, an axial gradient field can be produced in the region between the two permanent rings, with the field strength changing from-B0 to B0. A high gradient axial magnetic field has been built by using two axially magnetized permanent rings, the measured field results agree with the PANDIRA calculation very well. It is desirable that the field gradient can be varied to match various requirements. A method to produce the variable gradient field is presented. Axial gradient field can also be used as a beam focusing facility for linear accelerator if axial periodic field can be produced. Its magnetic field is similar to that of a solenoid, in which, large stray field will leak to the outside environment. A method for shielding the outside stray field is discussed.
Nano-sized semiconductors ZnO were synthesized with an upgraded reverse micelles by using DDAB (Didodecyldimethyl-ammounium bromide) as capped surfactants. The main advantage of this procedure is that the water needed to form micro reactors comes directly from intra molecule of Zn salt. The radius of nano-sized ZnO can be controlled by changing the concentration ratio of Zn salt and DDAB in organic solvent, and monitored by TEM images. XAFS spectroscopy is then used to recognize the distortion and the recombination on the surface of nanomaterial.
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