2003 Vol. 27, No. 3
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The radiation background of BES detector depends on the radiation level in the BES experimental hall. The way to reduce radiation level of experimental hall is very important for suppression of radiation background of BES and improvement of detection efficiency. The radiation level, the source and distinguishing feature of radiation background have been studied. The way to reduce the radiation has been discussed.
In this paper one loop SUSY QCD radiative correction to gb→tH－cross section is calculated in the context of Minimal Supersymmetric Standard Model. We found that non decoupling effects of SUSY QCD will occur if the gluino mass and the SUSY soft breaking parameter μ or At,Ab are at the same order and get large. The non decoupling contribution can be enhanced by large tan β and therefore large corrections to the hadronic production rates at the Tevatron and LHC are expected in the large tan β limit. The fundamental reason for such non decoupling behavior is found to be some couplings in the loops being proportional to SUSY mass parameters.
The squeezing property of the excited odd qs coherent state a+m qs α> o qs and excited even qs coherent state a+m qs α>e qs is numerically studied. It is shown that: (1) When the q(q≤1) or s is far from 1, the state a+m qs α> o qs and state a+m qs α> e qs exhibit strong qs squeezing, and as r2 increases the qs squeezing function Δe1(Δo1) exhibits the oscillating phenomenon of increasing-amplitude and increasing period. As m increases and s decreases, the amplitude of Δe1(Δo1) increases greatly. As s decreases, the period of Δe1(Δo1) increases but is independent of m. The m can be regard as the third parameter for controling the qs squeezing. (2) In general, the qs squeezing function Δe1(Δo1) is more sensitive to s than to q. That is, it is more resultful to control the qs squeezing by adjusting the parameter s than by adjusting the parameter q.
The influences of temperature on the constitutes, equations of state and masses of neutron star are studied in the frame work of the relativistic mean field theory for an interacting nucleons, hyperons, and mesons system. It is found that the appearing density of hyperons becomes smaller with temperature increasing. At higher hadron densities, the core of the neutron star is dominated by hyperons, in another words a neutron star transits into a hyperon star. The effects of temperature on the transition of a neutron star to a hyperon star are also investigated. The higher the temperature is, the smaller the transition density is. And it is also found that the equations of state for hadronic matter in the core region of a neutron star are approximately the same at different temperature. The calculated maximum masses of neutron stars are about 1.8M⊙, which are in consistence with the observation.
Energy and angular distributions of α fragments produced in 25Mev/u 6He+9Be break-up reaction were measured. We calculated double differential cross section and angle distribution of 4He fragment for 6He breakup reaction in terms of direct process theory including nuclear diffraction dissociation and stripping process based on Serber model. The influence of the diffraction dissociation and abrasion process to the break-up reaction is investigated by the Serber model. The theoretical analysis indicates that the large breakup cross section of 6He comes mainly from the low two-neutron separation energy, but the difference of radius size between 6He and 6Li has small influence on the results.
High spin states of 90Mo have been populated by the reaction 59Co(35Cl,2p2n)90Mo at beam energy of 116 MeV. A detector array consisting of 10 anti-Compton HPGe detectors was used for γ-γ coincidence measurements. Lifetimes of high spin states in 90Mo are determined by analysing the Doppler-broadened line shapes. Enhanced M1 transitions are observed in the positive-parity decay sequence and oblate deformation is suggested above 13+ state. A appreciable staggering of E2 transition rates associated with large B(E2) values is found in the high spin states with negative-parity. Transitions between positive- and negative-parity states exhibit enhanced B (E1) values, looking like existence of octupole correlation. However,90Mo does not lie in the mass regions of nuclei possessing octupole deformation predicted by theories.
The newly developed single trajectory quadrature method is applied to solve central potentials. First, based on the series expansion method an exact analytic solution of the ground state for Hulthen potential and an approximate solution for Yukawa potential are obtained respectively. Second, the newly developed iterative method based on Green function defined by quadratures along the single trajectory is applied to solve Yukawa potential using the Coulomb solution and Hulthen solution as the trial functions respectively. The results show that a more proper choice of the trial function will give a better convergence. To further improve the convergence the iterative method is combined with the variational method to solve the ground state wave function for Yukawa potential, using variational solutions of the Coulomb and Hulthen potentials as the trial functions. The results give much better convergence. Finally, the obtained critical screen coefficient is applied to discuss the dissociate temperature of J/ψ in high temperature QGP.
In the light of derivative coupling models, we argue that the zero point energy of the vacuum could not be simply thrown away at high temperature. So here the finite contribution which is temperature dependent has been separated from it and the influence of this correction on effective nucleon mass in nuclear matter has been studied.
The spin assignments of the signature partner bands in odd-A superdeformed nuclei in A≈190 region are discussed and the results are gived. To consider the decoupling effect in strong coupling limit of the particle-rotator model, in addition to using the ordinary I(I +1)expression to fit the experimental data of the energies of γ-transition in a single band, the double-bands method of analysis is used to fit the data in signature partner bands simultaneously. In the work, the convergence process of the series expansions is put stress upon, whereas taking how many terms exactly in the expression does not emphasized. Moreover, as well as the method fitting the physical quantity, by use of these series expansions the moments of inertia of the band heads are also calculated and the systematics is used for the spin assignments. In spite of the double-bands fitting method is more reasonable in physics, the practical calculation manifests that the single fitting method is equally effective and even more effective than the double-bands fitting method. It shows that the decoupling effect is small and the strong coupling limit is a good approximation in the A≈190 odd-A nuclei region.
Excitation functions of neutron, proton and α-particle emission prior to scission measured in the reactions 28Si+ 164,167,170Er→192,195,198Pb are studied using an extensive fission diffusion model and it is found that the model can well describe the trend of particle multiplicities of Pb isotopes measured experimentally as a function of the bombarding energy,which indicates the existence of isotope effects in prescission particle emission. Moreover, the dependencies of isotope effect on asymmetric fission and fissioning system size are also studied within the framework of a statistical model modified to include the effects of dissipation in fission by systematically investigating prescission particle evaporation of a light In isotope chain and a medium heavy Er isotope chain. Calculations show that in these regions the isotope effect exists,meaning that the isotope effect of prescission particle emission is a general effect. Furthermore this effect appears also in the case of asymmetric fission and it will be enhanced with increasing fission delay time. A new finding is that as the neutron-to-proton ratio of fissioning nuclei increases to a certain extent the prescission proton and α-particle emissions are no longer sensitive to the fission delay time scales. This means that for those neutron-rich fissioning systems proton and α-particle multiplicities will not be good probes for the study of nuclear friction in the fission of hot nuclei.
An algebraic routine for the evaluation of analytical expressions of multiplicity-free reduced coefficients of SfSf－1 is formulated based on the linear equation method and the analytical continuation of the rank f.As examples, ISFs of SfSf－1 for the coupling [f－1,1]·[f－1,1] and [f－1,1]·[f－2,1,1] are tabulated. It is obvious that the number of ISF tables is greatly reduced in comparison with numerical results calculated by using other methods.
Using distance dependent tight-binding molecular dynamics model (DDTB MD), the relative rotation processes in the sodium cluster collisions have been studied at the different incident energies and different impact parameters. It shows that for a given energy, there is a critical impact parameter. Under this impact parameter, the rotational energy increases rapidly with the increasing of the impact parameter, while above this parameter, the rotational energy decreases when increasing impact parameters. At lower energy, the relaxation time of the relative rotation is longer than that at higher energies.
The transverse anisotropy of particle emission is studied and a clear signature of the multipartiple azimuthal correlation is evidenced in Au+Au collisions at 600 A MeV within the Quantum Molecular Dynamics (QMD) model. The study indicates that the behaviour of elliptic flow in different events reflects the spatial anisotropy and the extent of particle rescatterings in the collisions.
Commodity hardware running the open source operating system Linux is playing various important roles in the field of high energy physics. This paper describes the PC-Linux-based Data Acquisition System of STAR TOFp detector. It is based on the conventional solutions with front-end electronics made of NIM and CAMAC modules controlled by a PC running Linux. The system had been commissioned into the STAR DAQ system, and worked successfully in the second year of STAR physics runs.
Scintillating fiber has the performance of high detecting efficiency and short response time. Scintillating fiber tracking combines the speed and efficiency of a scintillation detector with the flexibility and hermeticity. We study and test the performance of two kinds of scintillating fiber, Kuraray SCSF 81 of Japan and Bicron BCF10 of American. A set of experiment device testing single scintillating fiber performance is introduced. The experiment methods and measurement results of light yield, attenuation length, time resolution and spatial resolution are presented. The performance comparison for the two kinds of scintillating fiber is also given.
The physics design of BEPCⅡ storage ring requires that the kicker magnets must have properties of wide uniform field region with high field uniformity and low beam impedance. In order to satisfy these requirements, a new slotted pipe kicker magnet is proposed. The results from theoretical analysis and OPERA program simulation show that the kicker magnet satisfies all requirements of BEPCⅡ storage ring. In the range of Δx=±20mm, the field uniformity is ±0.6% in the central plane, ±0.7% in the y=5mm plane and ±2.9% in the y=10mm plane. The simulated results of MAFIA program also show that the beam impedance of the kicker magnet is lower than 0.022Ω, and it is less than the required value of 0.025Ω.
Mode coupling theory successfully explains the microwave instability, and the Vlasov equation is the basic of the theory. Fokker-Planck equation describes the distribution of the particles in bunch, which includes damping effect and the quantum excitation effect. We compare the Fokker-Planck equation with the Vlasov equation in the aspects of the origin, physics meaning, solution, and also introduce the method of polynomial expansion to solve the equation.
The paper presents the study of feasibility on the trace element analysis with high-energy resolution by PSS at synchrotron radiation as an exciting source. Results are that the absolute value of ～10－10g has been measured for elements of Ti and Cu in thin sample, the detection limit is about 1—10ppm order of magnitude for Cr in the substance of light base, and a well-proportional relation exists between the counts of net integrated area and the concentration of Cr in the samples of homogenized solution. These show that the PSS is feasible as a useful tool to analyze element with high-energy resolution.
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