2003 Vol. 27, No. 07
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Using Monte Carlo simulation,the process of J/ψ→γX→γηη′(η′→γρ0,ρ0→π+π-,η→γγ)is studied on BEPCⅡ/BESⅢ. Based on the better performance of BESⅢ and the large J/ψ data sample,it's possible to search for glueball state candidates and confirm their existence. Based on the study of this J/ψ radiative decay channel,it provides us some useful data for the selection of crystal BGO or CsI of electromagnetic calorimeter and for the selection of magnetic field intensity.
There are many models beyond the standard model predicting the existence of non-universal gauge bosons Z′,which can give rise to very rich phenomena. We calculate the contributions of the non-universal gauge bosons Z′,predicted by topcolor-assisted technicolor (TC2) models and flavor-universal TC2 models,to the lepton flavor-violation tau decays τ →l iγ and τ →l il jl k. We find that the branching ratio Br(τ →l il jl k) is larger than that of the process τ →l iγ in all of the parameter space. Over a sizable region of the parameter space,we have Br(τ →l il jl k)～10－8,which may be tested in the future experiments.
It is shown that antiburching effect is possible in the superposition state β>+e iφβ iδ>of the generalized Coherent states of the q-deformed non-harmonic oscillator.
In this paper we investigate the production of top-pion π0 t of the topcolor assisted technicolor (TC2) model with b quark pair at e+e- colliders. We find that the cross section of the process e+e－→b bπ0 t is larger than that of e+e－→b bH0 in the standard model,and is approximately the same as that of the process e+e－→b bh0(b bH0,b bA0)in the minimal supersymmetric model. With reasonable values of the parameter,the cross section can reach 10fb. The neutral top-pion π0 t may be observed directly via this process at the next linear colliders.
High-spin states in odd-odd 172Re have been investigated via the 149Sm(27Al,4nγ)172Re reaction through excitation functions, X-γ and γ-γ coincidence measurements. A level scheme consisting of three rotational bands has been identified for the first time,extending the high-spin studies of A≈170 odd-odd nuclei to the currently lightest rhenium isotope. The three bands have been assigned to be built on the πh11/2⊙νi13/2,πh9/2⊙νi13/2 and π1/2－⊙ν1/2－ configurations according to their rotational properties in quasiparticle alignments, signature splitting, in-band B(M1)/B(E2) ratios, level spacing systematics, band crossing frequencies, as well as the existing knowledge in neighboring nuclei. Low-spin signature inversion has been confirmed in the first two bands due to observation of signature crossing at high-spin states.
Cross sections for (n,2n),(n,p) and (n,n′α) reactions have been measured on Gallium isotopes at the neutron energies of 13.5-14.6MeV using activation technique. The data of the cross sections are reported for the reactions of 69Ga(n,2n)68Ga,69Ga(n,p)69mZn,71Ga(n,p)71mZn,and 71Ga(n,n′α)67Cu. The cross sections of 69Ga(n,2n)68Ga reaction are 794±31,869±35 and 986±39mb at 13.5±0.2,14.1±0.1 and 14.6± 0.2MeV incident neutron energies, respectively. The cross sections of 71Ga(n,n′α)67Cu reaction are given:1.3±0.1,1.7±0.1 and 2.5±0.1mb at 13.5±0.2, 14.1±0.1 and 14.6± 0.2MeV, respectively. The cross section of 69Ga(n,p) 69mZn reaction is 21.5±1.0mb at 14.1±0.1MeV. The cross section of 71Ga(n,p) 71mZn reaction is 12.4±0.7mb at 14.1±0.1MeV. The neutron fluences are determined by the cross sections of 93Nb(n,2n)92mNb reaction.
Within the isospin dependent Extended Brueckner-Hartree-Fock framework,the three-body force effects on the single particle potentials of a neutron and a proton in isospin asymmetric nuclear matter and their isospin denpendence have been investigated. It is shown that the contribution of the three-body force is repulsive. At low density, i.e., around and below the empirical saturation density, the effect of the three-body force is rather small, while as increasing density, it becomes more and more pronounced. It is also found that at a given density, the three-body effect increases with isospin asymmetry.
With use of the Bonn potential, a modifed relativistivic mean field model is proposed when the effects of in-medium hadron masses are considered by the Brown-Rho scaling. Then, the model is extended to investigate the equation of state of nuclear matter at finite temperature when the scaling parameter is caliberated by the properties of nuclear matter ground state.
How to calculate the γ-ray emission probability (absolute intensity) for isomeric transition decay is briefly introduced. The examples are given to illustrate their applications. The physical consistent checking and some discussions are also given.
We have carried out a study of A～50 isotopes in the framework of axially deformed relativistic mean-field theory. The ground-state properties of Ti(N22-32), Cr(N20-34) and Fe(N22-36) isotopic chains have been obtained. The separation energies of 45Cr, 46Cr,49Fe,50Fe,53Ni and 54Ni are given, from which we have investigated the stability of the nuclei. We concluded that there is little possibility to reach the high-spin states of 45Cr and 49Fe.
Nuclear lifetime shift of charged atom, due to lack of internal conversion (isomer) or electron capture transition (β decay), is analyzed. Theoretical predict is given, that electron density of inner shell at nuclear surface decreases and energy level also decreases with increasing of charge state, nuclear lifetime increases slightly with previous reason but increases with a jump when energy level drops to a critical value. The shifts of halflife are compared for internal conversion with different nuclear decay energy and different type of transitions. A common used computer code of this calculation created by ourselves, and the calculation results are compared with experiment one.
Time-dependent fission rate is calculated numerically by simulating a set of Langevin equations. The results show that in the stationary limit the fission rate does not approach to those based on both Kramers formula with constant mass and modified Kramers formula, whenever the temperature is higher than a half of the fission barrier. Considering coordinate-dependent mass plays an important role in the fission rate, we proposed an effective potential, thus an improved Kramers formula is obtained, which is still valid when the temperature is increased to the same as the barrier height. The present results are in good agreement with the fission rate determined in the scission point by using Langevin simulation.
We developed a new kind of material, which is used to construct the prototype of a large area resistive plate chamber (RPC). In this paper, the structure of RPC, the curves of efficiency, counting rate, dark current, multiple hit and signal amplitude versus high voltage measured using cosmic ray are presented. It shows that the RPC efficiency is close to 98%, counting rate and dark current are superior to currently operating detectors worldwide. Its performances well satisfy the requirements of high energy physics experiments.
A time correlated single-photon counting technique of emission time measurement for plastic scintillating fibers is given. The time response of the test system is studied and calibrated with Cherenkov radiations. The emission time properties for two different kinds of plastic scintillating fibers, Kuraray-SCSF81 and Bicro-BCF10, are obtained.
The methods for calculating the electrical field strength in gas detectors have been introduced in this paper. The process to calculate the electrical field in gas detectors with complex electrode structure based on ANSYS has been presented and the electrical field calculation of MSGC detector has been given as an example. The effect of electrical field on the performance of gas detector has also been discussed.
A method based on the transverse particle motion equation is described for the calculation of beam acceptance for RFQ accelerators. The result is given for a four-vane type RFQ accelerator with specific structure parameters. The system acceptance for proton beam is 0.0153 cm·rad in x-x′ phase space, and 0.0114 cm·rad in y-y′ phase space. The method can also be applied for the calculation of acceptance for other RF accelerators with known structures and linear transverse electric fields.
The method which used the spark gap switch to sharpen the output of the modulator accelerator was presented. Through experiments on the pulse modulator accelerator, a rectangular-like waveform with voltage 500kV, pulse width 900ns, rising edge 80ns, trailing edge 100ns is obtained, and repetitive reliable operation is performed at the frequency of 1Hz.
The characteristic and performance of ripple feedback loop for output sub-harmonic suppression in BEPC main magnet power supply were studied, the limits of the loop effect are analysed and explained. The experimental studies on active filters to attenuate the power supply output ripple are described, the structure and design of the filter are also introduced in this paper.
For the beam transport system in storage ring, linear coupling is mainly caused by skew quadrupole and longitudinal solenoid field. It leads to emittance exchange and beam envelope augment. By using betatron motion of single particle in the presence of skew quadrupole and longitudinal solenoid field, the effect of the beam linear coupling is preliminarily investigated. Beam emittance variation due to skew quadrupole is obtained too.
With Lie algebraic methods, we analysed the nonlinear transport of particle motions in electrostatic quadrupoles up to third order. The procedures are: first, set up the Hamiltonian for the electrostatic quadrupoles, then expand the Hamiltonian into a sum of homogeneous polynomials of different degrees, finally, calculate the particle's nonlinear trajectories up to third order. Higher orders could be obtained if necessary.
The voids in α-Al2O3 irradiated by 85 MeV 19F ions of 5.28×1016cm－2 have been observed during the post-annealing by a positron annihilation lifetime technique for the first time. The voids start to appear at 450℃. The void radius keeps nearly constant at ～0.29nm and the number of voids increases with increasing the annealing temperature from 550℃ to 750℃. Afterwards, the radius of voids increases rapidly with the annealing temperature and reaches 1.10nm at 1050℃.
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