2007 Vol. 31, No. 5
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Based on the experimental data of the cross section e+e－→π+π－π+π－ measured by the BABAR collaboration, we apply the theoretical cross section deduced from the extended VMD (Vector Meson Dominance) model to fit these experimental results. It is the first time that the isovector form factor and the relevant parameters are obtained through one decay mode.
The decay of D0→K－π+ is a golden channel in the study of D0-D0 mixing at ψ(3770). The requirements of excellent K/π separation will play an essential role in the mixing search. A technique was developed to precisely extract event start time (t0) with TOF measurements in multiple charged tracks event at BESⅢ. After the t0 extracting algorithm, the time resolution of double-layer TOF reduced from ～78ps to ～64ps, the upper limit of D0-D0 mixing rate at 95% CL can be improved by a factor of 7% in 20fb－1 ψ(3770) data.
Based on the ultraviolet/infrared scale separation of the connection decomposition variables, we propose that at the classic level the strong-coupling limit of the Yang-Mills theory vacuum behaves as a black hole with regard to colors. With this idea, we prove that there exists a dual superconductor solution for the strongly-coupled Yang-Mills theory, whose vacuum is made up of a many-body system of magnetic charges at the quantum level. The classic average of the theory reproduce the dual Abelian-Higgs model. This model predicts a result which is consistent with recent lattice simulations. The vacuum of the SU(2) gluodynamics is at border between type-Ⅰ and type-Ⅱ. The dual Meissner effect of Chromo-electric field is discussed by solving the dual Abelian-Higgs model.
The neutron emission double-differential cross sections(DDXs) of n+9Be and 6,7Li were measured at incident neutron energies of 8.17 and 10.27MeV. At 10.27MeV, the influence of breakup source neutrons from D(d, np) reactions was eliminated by using the combination of abnormal and normal fast neutron TOF spectrometers. The measured TOF spectra were analyzed by detailed Monte-Carlo simulation and the DDXs were determined by comparing the measured TOF spectra with simulated ones. The cross sections were normalized to n-p(normal geometry measurement) or n-C(abnormal geometry measurement) scattering measurement. The measured results were compared with the evaluations and the other measurements. A theoretical model based on the Hauser-Feshbach and exciton model for light nuclei was used to describe the double-differential cross sections of n+6,7Li. Good agreement between theoretical calculation and measurement has been obtained.
Using six different high-threshold neutron-activation detectors, the activation reaction rates are obtained with and without the Al reflector. Measured reflectivities of high-energy neutrons from Al reflector are also obtained as the ratio of measured data and range from 1 to 1.14. For different activation detectors, the shape of the reflectivities as function of measurement angles is rather similar. The intensity of the reflected high-energy neutron field is high at large angles and smaller towards smaller angles. With increasing thresholds of the activation detectors, the reflectivities decrease. Evaluated total uncertainties of reflectivities are 3.4%—4.2%. Calculated results of reflectivities agree with the experimental results at the majority of the measuring points.
We present a theory to describe multiple scattering (MS) with an arbitrary basis. This framework allows us to select a set of new basis that exhibits better convergent properties than the usual spherical wave basis. Therefore, it enables us to perform faster and less memory-consuming calculations. Although the method outlined here is quite general, it gives a better description of the scattering properties and consequently reduces the size of the two block matrices involved in the MS calculation.
The proton elastic scatterings on 14Be, 16O and 12C at the intermediate incident energies of 200, 400 and 800MeV, are investigated within the relativistic impulse approximation (RIA). The effect of the incident energy on three observables, the differential cross section, the analyzing power and the spin rotation function, is discussed. It is shown that in the region of small scattering angle, the halo neutron effect on the observables exhibits an unchanged tendency with the variation of the incident energy of proton in the intermediate energy region.
Reactions of bombarding important target materials in the Accelerator Driven System (ADS), such as 204Pb,206Pb,207Pb,208Pb, 209Bi,196Hg,198Hg,199Hg, 200Hg,201Hg,202Hg and 204Hg etc., with protons are calculated in terms of the optical model, the intra-nuclear cascade mechanism for nucleon emission, the pre-equilibrium theory based on exciton model, the evaporation model, the pick-up mechanism and the direct reaction theory in the energy range up to 250MeV. In particular, the cross sections of the (p,kn), and (p,kpkn) reactions and the spectra of particle emissions are studied. The calculations show that the pre-equilibrium (including cascade) mechanism is much stronger than the other mechanisms in the higher energy region. The parameter DK of the exciton model and ccg1 in the single particle energy density dominate the shapes of the cross section curves of the (p,kn) and (p,kpkn) reactions and the energy spectra of emitting protons and neutrons. The pick-up mechanism plays an important role in emitting composite particles (α,D,T,3He).
Nuclear matter incompressibility is discussed by the monopole compression modes in nuclei in the framework of a fully consistent relativistic random phase approximation, based on effective Lagrangians with a mixed isoscalar-isovector nonlinear coupling term. A predicted value of the matter incompressibility coefficient is given by comparison between experimental and calculated energies of the isoscalar giant monopole resonance (ISGMR) in nuclei 208Pb, 144Sm, 116Sn and 90Zr. The new isoscalar-isovector nonlinear coupling softens the nuclear matter symmetry energy without ruining the agreement with experimentally existing ground state properties. The effect of the softening of the symmetry energy on the ISGMR is discussed.
TPC is widely used as a tracking detector in many colliding beam experiments. A GEM-based TPC is under construction and the working gases are to be considered. The paper summarizes the transport properties of ionization electrons generated in gas mixtures that are suitable to work in TPC with GEM as its endcap detector. The lifetime of electrons, the drift velocity and diffusion are simulated and investigated, with the help of Garfield. With a theoretical analysis, a gas mixture of Argon, CH4 and CF4 is proposed. The performance of GEM with the proposed gas is excellent with regard to the gas gain and energy resolution, which makes it a promising candidate for the future GEM-based TPC.
This article is about the study of two kinds of EMI 8" PMTs, D642KB and 9350KA. Several characteristics including relative quantum efficiency(QE), linearity, gain, dark current, afterpulse ratio and incident angle effect have been tested. Specially, dedicated systems have been set up for the measurements of relative quantum efficiency and incident angle effect. The performances of the two kinds of EMI PMTs are described here.
The correction formulas of simple, more complex and universal decay schemes about gamma-rays cascade radiation coincidence summing were deduced based on basal concepts. And then using them calculated the correction coefficient of γ-rays cascade radiation coincidence summing of 133Ba and 60Co. At the same time, it was pointed out that the correction formulas given in some literatures is improper.
Due to the change of the hardware and high voltage during the small angle GDH experiment data-takeing, the CO2 gas threshold Cherenkov detector on HRS at Hall-A in Jefferson Jlab(JLab) was calibrated for seven times. The ADC signals of the single photo-electron peak for all ten PMTs were scaled to two hundred. The electrons could be separated from π by the detector after the calibration correction.
Based on the experimental results of the complex DC-SC photocathode injector (DC gun and 1+1/2cell superconducting cavity) at Peking University, an improved injector design is proposed. The new injector can provide high average current electron beams with bunch charge of 100 pc, cw operation, low transverse emittance and short bunch length. The optimization of the DC gun and superconducting cavity of the upgraded injector, structure design of the injector are presented in this paper.
We have derived the global band gaps for general two-dimensional (2D) photonic crystal microwave accelerating structures formed by square or triangular arrays of metal posts. A coordinate-space, finite-difference code was used to calculate the complete dispersion curves for the lattices. The fundamental and higher frequency global photonic band gaps were determined numerically. The structure formed by triangular arrays of metal posts with a missing rod at the center has advantages of higher-order-modes (HOM) suppression and main mode restriction under the condition of a/b<0.2. The relationship between the RF properties and the geometrical parameters have been studied for the 9.37GHz photonic crystal accelerating structure. The RS, Q,RS/Q of the new structure may be comparable to the disk-loaded accelerating structure.
We are developing a high specificity detector for detecting the increased metabolic rate of breast tumors. Positron emission mammography (PEM) provides a highly efficient, high spatial resolution positron imaging system. PMT plays a very important role in PEM detectors, because most of the systems consist of scintillator arrays coupled with PMT. Our detector is composed of 20×20 arrays of 2mm×2mm×20mm of Bi4Ge3O12 (BGO) scintillators and a novel flat panel position-sensitive PMT (FP-PS-PMT) -Hamamatsu R8400-00-M256. Spatial resolutions of 2.0mm FWHM and energy resolutions of 23% FWHM are achieved.
We investigate dynamics of the multipartite entanglement in the Heisenberg model and give analytical expressions of the average concurrence 〈C〉 and the multipartite entanglement measure Q. It is found that both 〈C〉 and Q initially increase with the increase of the scaled time t, and finally reach a plateau, oscillating irregularly around a steady value. And for the case of N〈C〉, this steady value is nearly independent of the length of the chain, and only determined by the NNN coupling constant J.
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