2004 Vol. 28, No. 8
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We have studied a neutral top pion production process e+e-→tπ0t in the topcolor assisted technicolor(TC2)model.The studies show that the production cross section is larger than that of the process e+e-→tH both in the standard model(SM)and in the minimal supersymmetric SM.With peasonable values of the parameters in TC2 models,the cross section can reach 20fb.The neutral top pion π0t may be direct observed via this process.
In this paper,we present the realization of unitary transformation that is corresponding to symplectic transformation of coordinate on noncommunicative R2N,and give out the transformation of wave function caused by the unitary transformation,i,e.,it is the matrix unit of unitary transformation.
High spin level structure of doubly odd nucleus 140Pr has been investigated using in beam γ spectroscopy techniques by means of the 130Te(14N,4n)140Pr reaction at beam energy of 58MeV.γ-ray excitation functions,γ-ray singles and γ-γ-t coincidences were measured experimentally.The level scheme of 140Pr,including 27 new levels and 42 new γ-rays,was established for the first time up to 4717.3keV in excitation energy.Based on the measured γ-ray anisotropies,spin values were suggested to the levels in 140Pr.Several quasiparticle configurations are discussed on the basis of systematics in the neighboring odd odd nuclei,and interpreted qualitatively.
We have measured the reaction cross section σR of 17C on the carbon target at the intermediate energy of 97A MeV by using transmission method.finite-range Glauber model has been employed to investigate the density distribution of 17C by fitting the present result and the previous result of interaction cross section σI.By contrast with the result from the analysis of σI,a tail in the neutron density distribution of 17C is found necessary to interpret the present result.Considering the configuration of the valence neutron,a dominant 1d5/2(77±21%)occupancy is found,which is in agreement with results of momentum distribution measurements.
An exactly solvable mean filed plus nearest orbit proton proton and neutron neutron pairing interaction model for the unifled description of well deformed nuclei in actinide region is proposed.Binding energies,pairing excitation energies,and even odd mass differences of 227-233Th,232-239U,236-243Pu isotopes and 228Ra-229Ac-230Th-231Pa-232U,232Th-233Pa-234U-235Np-236Pu,and 236U-237Np-238Pu-239Am isotones are calculated and compared with the corresponding experimental values.
Recently,the ratio of electric form factor to magnetic form factor for the neutron GEn/GMn,which contains important pieces of information on the internal structure of nucleon,was measured at the Thomas Jefferson National Accelerator Facility(JLab).The traditional relativistic constituent quark(RCQ)model appears to be successful in explaining the two form factors for the proton GEp/GMp,however the calculation results for the neutron is much bellow the experiments.For interpreting this phenomenon,we investigate the effects of SU(6) breaking.It is shown that the calculation results gets better close to experiments.
The method of calculating IXK/Iγ(343keV)ratio and the analysis and the comparision of experimental measurement for 175Hf decay are introduced.Based on the data analysis,the emission probability of 343 keV γ-ray, Pγ(343keV)=0.869±0.004,is obtained.Absolute intensities of radiation data for 175Hf decay are calculated and recommended.
The mass number dependence and the neutron incident energy dependence of the radiative capture cross sections from various reaction mechanisms of the neutron radiative capture process have been examined in the nuclear mass region A<100.Two reaction mechanisms are considered.They are compound nucleus statistical process and two nonstatistical process,i.e.,radiative capture in compound elastic scattering channels and direct semidirect radiative capture in shape elastic scattering channels.Incident energy of neutron is chosen in the region of 0.1-20MeV.The calculated results are given and compared with the experimental values for 27Al,40Ca,63Cu and 93Nb.The variational pattern is analyzed and discussed.
Starting from the QCD potential which emerges from the effective dilaton gluon coupling,the energy levels and the widths of the leptonic decay and radiative transition are calculated for heavy mesons(c and b)and compared with that of the Cornell potenial.The better results are obtained with respective to the Cornell potential.The dilaton mass is estimated to be 57MeV.
Effects of target deformation on the capture and fusion processes of the 48Ca+238U system are investigated in the framework of extra push model.The reults of our investigation indicate that target deformation enhances the capture and fusion cross sections for heavy system forming superheavy nuclei,and broadens the spin distribution of the corresponding compound nuclei at near and sub barrier energies.
On the basis of model proposed by Blaizot et al.,we take into account the effects on J/ψ suppression in AA collisions of the number fluctuations of participants and NN collisions,and analyze the data of the NA50 Collaboration in Pb-Pb collisions at 158GeV/c.The theoretical results fit the data well.
We studied the effect of Coulomb interaction on the isospin fractionation in intermediate energy heavy ion collisions by using isospin dependence quantum molecular dynamics model (IQMD).The results show that Coulomb interaction reduces the isospin fractionation process whatever the system mass,beam energy and system neutron proton ratio are,because Coulomb interaction is repulsive for proton.The more bound protons became free under Coulomb interaction,which produces neutron poor gas phase and neutron rich liquid phase,thus isospin fractionation degree is weaken.On the contrary,the symmetry potential is repulsive for neutrons and attractive for protons in neutron rich systems.The bound neutrons more than protons became free,which produces neutron rich gas phase and neutron poor liquid phase,so the isospin fractionation degree increases.Total effects of the Coulomb interaction and symmetry potential make the isospin fractionation degree to be in between those induced by themselves individually.
The passing probability of nuclear fusion and the fission rate at the saddle point is calculated by an improved scheme with test particle muti passing over the saddle point,where a strong back streaming effect around the saddle is found and considered.It is also found that the back streaming becomes stronger if the post saddle barrier gets smoother.Fusion probability and fission rate,which are simulated usually via test particle first passing over the saddle model,are decreased by the back streaming effect.
The photon detection efficiencies of Monte Carlo simulation and data are studied using three methods in the decay of J/ψ→ρπ at BESⅡ.The results show that the Monte Carlo can simulate the photon detection efficiency of data in the precision of 1%-3%.The source of discrepancy between Monte Carlo and data is also studied in this work.The sample of e+e-→γe+e- at the center of mass energy of s =3.770GeV is used to study the detection efficiencies of the photons with the energies greater than 1.4 GeV for Monte Carlo and data that are both 100%,and the difference of the photon detection efficiency between Monte Carlo and data is less than 1%.
The YBJ ARGO experiment is presently in the mounting and debugging phase at the Yangbajing High Altitude Cosmic Ray Laboratory,Tibet,China.The YBJ ARGO EAS array is composed of bakelite RPCs which operate in the streamer mode.The digital read out,performed by means of read out strips,allows measuring the secondary particle number of small size air showers.To extend the dynamic range of the secondary particle number density up to 104/m2,thus to measure the component and spectrum of primary cosmic rays at the knee region,it is necessary to implement the analog read out of the RPC,which is achieved by encapsulating each RPC with two Big PADs.This paper reports on the primary analysis of the analog read out signal of the Big PAD under different gas mixtures,including the amplitude distribution and ratio of the single streamer signal.
The Cherenkov counter used for selecting electrons of the test beam has been studied in this article.The design,manufacture,assembly and testing of the Cherenkov counter are described.And the performance of this counter is measured.The CO2 gas is used as Cherenkov radiator,the XP2020Q photomultiplier is applied for recording signals of the Cherenkov light.The (99.0±0.5)% efficiency of the electron selection has been reached.
An HPGe detector has been constructed for the direct detection of Weakly Interactive Massive Particles(WIMPs).The supersymmetric parameter space for WIMPs detection using this HPGe detector which has 100eV low energy threshold and 5g mass has been explored based on the so called Minimal Supersymmetric extension of the Standard Model(MSSM).The result shows that it will be possible to provide the most stringent upper bounds of WIMP nucleus spin independent cross section at the lower WIMPs mass region.
The precept of DC-SC photoinjector is to combine a DC photoca thode electron gun and the superconducting cavity together.This scheme is specially adequate to provide the high average beam current.In this paper,authors have described the drive laser system for the DC SC photoinjector of PKU version.This system is mainly composed of GE 100 XHP laser,a passive mode locked Nd:YVO4 laser,CLX 1100 timing controller from TBP,Switzerland,self developed high efficiency SHG and FHG and laser beam transmission system.After experimental test,the laser power of 266nm is more than 1 W,the jitter between laser pulses and the RF reference signal is less than 1 ps.By use of this laser system,we have observed more than 500μA electron current from Cs2Te cathode.
We have designed and built an emittance scanner which was installed at the beam line LECR3 of the heavy Ion Accelerator Facility in Lanzhou.The scanner measures the emittance of beams from the ECR ion source by the electric-sweep method,named as Electric-Sweep Scanner(ESS).From analyzing the measured results we found it is contrary to the behavior expected from normal theory of ECR plasma.Typical results are as follows:when the extracted voltage is 15.97kV,total current is 190μA,the horizontal and vertical emittance of O4+ are 137πmm·mrad and 120πmm·mrad respectively.
The flat top technology is widely used to improve beam quality and raise beam current in many cyclotrons.The fundamental of the flat top technology is described in this article,and the effects of the main parameters of the flat top cavity,such as the frequency,the voltage and the stability,on the longitudinal phase space is discussed too.
Periodic multilayers of W/C and Mo/Si have been developed with magnetron sputtering technology.The parameters of period and thickness are adjusted so that the first Bragg peak appears at the Brewster angle when the photon energy is in the vicinity of K edge of carbon and L edge of silicon respectively.The experiment was implemented at Beijing Synchrotron Radiation Facility(BSRF).The reflectivities of multilayer Mo/Si and W/C can reach 32.3% at 89eV and 4.18% at 214eV respectively near the Brewster angle.The feasibility of setting up polarizer with multilayers is discussed in this paper.
By using virtual photon Compton scattering,a theory of synchrotron radiation is presented.The calculation results of wavelength is consonant with experimental data.Also,the properties of emission mainly in the plane of the electron orbit and the properties of a wide spectrum could be explained.In the case of lower energy of particle,the theory of cyclotron radiation could be derived according to the theory.
Undulator is a key device of Free Electron Laser facilities.Hybrid Undulator with superimposed strong focusing is of many advantages,yet difficult to be developed.This paper describes the essential work for this kind of undulator,the magnetic design optimization of a ten period undulator.
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