2006 Vol. 30, No. 3
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A search for flavor changing neutral current (FCNC) and lepton number violation (LNV) decays of charmed D mesons is performed using 33pb－1data around Ψ(3770) collected by BESⅡ detector at BEPC. Four decay modes of D0(K0e+e－,Φe+e－,ρ0e+e－ and K*0e+e－) and six decay modes of D+(K－e+e+,K+e+e－,π－e+e+, π+e+e－,K*－e+e+ and K*+e+e－) are presented. No evidence is found for the above decays, therefore, the upper limits at 90% confidence level are set. The limits of two D+ decays modes,D+→K*－e+e+和D+→K*+e+e－ have not been reported previously.
A new symplectic Lagrangian density and Faddeev-Jackiw (FJ) generalized brackets of the gauge invariant self-dual fields interacting with gauge fields have been obtained and FJ quantization of this system has been presented. Furthermore, the FJ method is compared with Dirac method and the results indicate that the two methods are equivalent in the quantization of this system. After analizing, it can be found in this paper that the FJ method is really simpler than the Dirac method, namely, the FJ method obviates the need to distinguish primary and secondary constraints and the first- and the second-class constraints. Therefore, the FJ method is a more economical and effective method of quantization.
A calculation procedure for effective Abelian-Higgs-like action is presented via Faddeev-Niemi decomposition of SU(2) gauge field. A natural gauge fixing is explicitly identified in the decomposition and intrinsic relation between Abelian projection and the symmetry-breaking of the Yang-Mills dynamics in infrared limit is illustrated. A London like equation is derived for chromo-electronic field.
The β+/EC decay of doubly odd 176Ir has been investigated using 146Nd(35Cl, 5nγ)176Ir heavy ion fusion evaporation reaction at 210MeV bombarding energy. With the aid of a helium-jet recoil fast tape transport system, the reaction products were transported to a low-background location for measurements. Based on the data analysis, the previously published γ rays in 176Ir decay were proved, moreover, 3 new levels and 10 new γ rays were assigned to 176Ir decay. The new level scheme of 176Os with low excitation energy has been established. The time spectra of typical γ rays clearly indicate a long-lived low-spin isomer in 176Ir nuclide.
The pseudospin symmetry is systematically investigated by solving the Dirac equation with an (scalar and vector) Woods-Saxon potential. We find that the splittings of pseudospin energy and the lower component of pseudospin doublets are sensitive to the nuclear radius and the nuclear diffusivity, but to the depth of nuclear potential. The splitting of pseudospin energy with larger n or l is more sensitive to the values of the parameters. The energy level crossing is also found for some pseudospin partners with variation of the nuclear mean field. With the increasing of nuclear radius and nuclear diffusibility, the splitting of the lower component of pseudospin doublets diffuses toward the nuclear surface and reaches the largest value on the nuclear surface. The splitting of pseudospin doublets increases with increasing nuclear diffusibility but decreases with increasing nuclear radius and the depth of nuclear potential. Because the variations of the parameters R and V0are related with the number of nucleon and the characteristics of nuclear surface can be described by the parameter of diffusibility, the conclusions obtained are meaningful for analyzing nuclear properties.
One meson exchange potential of the KK system is studied.When momentum-squared terms are included, the one meson (ρ,ω,φ) exchange potential alone fails to produce any KK bound state. With the Coulomb potential, K+K－ can form atomic bound state---the kaonium. The influence of the one meson exchange potential on the ground state energy of kaonium and its decay widths to ππ and πη are evaluated.
The particle evaporation in the fission process of 100Sn is studied using a diffusion model. It is shown that the shell influences strongly the proton emission whereas its effect on neutron emission is negligible, in contrast with the case of 132Sn. It is due to the effect of the difference of neutron-to-proton ratio, N/Z,of the systems. This conclusion is further verified by comparing particle emission between 100Sn and 104Sn. Calculations indicate that high excitation energy weakens this N/Z effect.
The properties of the nuclei belonging to the newly observed nuclei starting from 288115 have been studied with the generalized liquid drop model connected with WKB approximation. The calculated results have been compared with the results of the DDM3Y theory and the experimental data. The half lives of this new alpha decay chain have been well tested from the consistence of the macroscopic, microscopic and the experimental data.
The spectral function of rho meson in hot and dense pion medium is studied within an effective model which describes the ρ-π coupling. The results from numerical calculation show that the spectral function becomes wider and the position of the peak moves towards the high invariant mass region when the temperature and the pion chemical potential increase.
A new gamma-ray detecting device called ICI detector has been developed and tested. Like vacuum Compton diode(VCD) and dielectric Compton diode(DCD) generally used in pulsed gamma-ray measurements, ICI detector operates by utilization of the Compton effect and has low sensitivity to gamma-ray fluxes, very fast time response, large linearity and wide dynamic range, it is desired for using the device to measure intense and rapidly changing gamma-ray fluxes. Compared to the existing VCDs and DCDs, the detector requires no vacuum in operation and the active volume is only 2mm thick.
With an excellent time resolution, the Multi-gap Resistive Plate Chamber (MRPC) has been applied as TOF detector in particle physics experiments. We constructed more than 30 MRPC modules that were set up on the tray of RICH-STAR successfully. By the program of Magboltz, the parameters of working gases in MRPC were calculated. Based on the detector physics the relation between MRPC performance and working gas was analyzed,which is helpful to optimize the proportion of gas mixtures for RPC and MRPC.
For the Phase 2 of HLS (Hefei Light Source)Project, many sextupoles and octupoles have been installed in the machine to improve the operation condition. These nonlinear elements will introduce nonlinear effects to the beam dynamics. In this paper, we apply Frequency Map Analysis to the HLS ring. By analyzing the resonance lines on the tune map, we find that the calculated lattice of GPLS mode lies on the weak chaotic zone, and the operating mode is better.
To eliminate the higher order modes (HOMs) in superconducting cavity, an improvement study on HOM coupler has been done. With Code HFSS,the HOM coupler for 1+1/2 Cell superconducting cavity of the Peking University has been designed and optimized. The improved HOM coupler can absorb main HOMs out to －15dB from －40dB, which proves this HOM coupler to be effective.
For the sake of acquiring the shorter beam bunch length a 500MHz RF system will be adopted in Beijing Electron-Positron Collider Upgrade (BEPCⅡ) project to replace the existing 200MHz RF system. The designed beam current of BEPCⅡ is 0.91A which put forward high requirements to the parameters of RF power source. According to the BEPCⅡ general goals and the related requirements with RF system we completed the BEPCⅡ RF power source layout and all technical designs including the parameters for the transmitters and the circulators, completed the designs of all auxiliary systems. Based on these designs, the first BEPCⅡ RF power source including the transmitter and the circulator as well as the auxiliary systems have been established and passed the acceptance test.
When charged particle beams traverse in an accelerating structure, the excited wake fields may dilute the beam energy spread and emittance. In order to estimate the wake field effects on the beam dynamics properly, it is very important to calculate the wake fields precisely. In this paper, the calculation methods of the short range, middle long range and super long range wake fields in constant gradient structures are systematically studied, and the expression of the super long range longitudinal wake field is first given. In addition, the wake fields for the BEPCⅡ Linac's disk-loaded structures are calculated by using analytical methods and various computer codes, the consistency and some deviations of the results obtained by different calculation methods are also discussed.
Electron cloud instability (ECI) may take place in a storage ring when the machine is operated with a multi-bunch positively charged beam. Transverse blowup due to electron cloud has been observed in some machines and is considered to be a major limit factor in the development of high current and high luminosity electron positron colliders. With a streak camera, the transverse blowup along the bunch train was first observed in an experiment at the Beijing Electron-Positron Collider (BEPC) and the simulation results were used to compare with the observation.
A depth of interaction (DOI) detector for γ-rays has been developed for a high-resolution positron emission tomography (PET) system dedicated to small animal studies. It is well known that different surface treatment on the crystals influences the total light output, and consequently affects the performance of the detectors. In order to optimize the performance of the new proposed DOI detector, we have focused on the comparison of the detectors consisting of narrow LSO crystals with different surface conditions. We observed a significant improvement in crystal identification, energy resolution, time resolution and detector response resolution for constructing detectors using polished crystals compared to those using roughened LSO crystals. The results of this study can provide useful information for LSO detectors to be used in practical PET systems.
It is investigated experimentally how the thermal properties of some specimens of thermal control coatings change with irradiation fluence ranging from 1.0×1011p/cm2 to 1.0×1017p/cm2 with 110keV proton beam. It is shown the thermal properties of all the 6 specimens examined nearly do not change at exposure of 1.0×1011p/cm2. The solar absorptance of some specimens of thermal control coating of low absorptance increases at first and decreases whereafter as the proton fluence rises from 1.0×1012p/cm2 to 1.0×1016p/cm2. This indicates that the irradiation method may be used to promote the thermal properties of some thermal control coatings of low solar absorptance.
Based on our previous work, the phase state and phase operator introduced by Pegg and Barnett are generalized to two-mode q-deformed circumstances. With the aid of numerical method, the phase probability distributions of q-deformed pair coherent state are investigated.It is shown that these probability distributions of the state are regulated by the parameters of phase, the q-number and the magnitude of │ξ│.Therefore, the q-deformed pair coherent state exhibits different quantum interference properties.
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