2002 Vol. 26, No. 2
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With 7.8 million produced J/ψ events collected by the BES detector at the BEPC, the decay J/ψ→Σ0Σ0 is analysed. The branching ratio is measured to be BR(J/ψ→Σ0Σ0)=(0.97±0.04±0.24)×10－3. The angular distribution is of the form dN dcosθ=N0(1+α cos2θ) with α value of －0.21±0.27±0.13.
The first observation of the color suppressed decay mode B0d→D(*)0π0 by the Belle and CLEO Collaborations makes a quantitative analysis of the isospin relations for the amplitudes of B→D(*)π possible. The strong (isospin) phase difference in B→Dπ transitions is found to be about 29° by use of the Belle data or 26° by use of the CLEO data, implying that final state interactions might not be negligible. Applying the factorization approximation to I=3/2 and I=1/2 isospin amplitudes of B→Dπ decays, we obtain the ratio of the effective Wilson coefficients a eff 1and a eff 2∶ a eff 2/ a eff 1≈0.27. A similar analysis shows that the magnitude of final state interactions in B→D*π might be comparable with that in B→Dπ, and the factorization hypothesis works consistently in both of them.
Study of in beam γ ray spectroscopy of 127I has been performed using 124Sn(7Li, 4n)127I reaction at 32 MeV beam energy. A new level scheme of 127I has been established including 25 new levels and 52 new γ transitions. Negative parity levels based on 11/2－ π h11/2 particle state have been observed up to (35/2－) extending our knowledge of decoupled structures to the heavier iodine isotope. Two ΔI=2 yrast positive-parity levels have been proposed to be associated mainly with the πg7/2 configuration due to observations of several strong inter band transitions. Two weakly populated ΔI=2 positive parity levels and a high-lying ΔI=1 cascade have been newly identified and tentatively assigned as πd5/2 one-quasiparticle and three quasiparticle bands, respectively.
With the data of recent measurements of the JACEE, RUNJOB and SOKOL experiments, and under the assumption of rigidity cut-off model, a new primary cosmic-ray energy spectrum and chemical composition in 1014—1016eV energy region are derived. EAS simulations using CORSIKA, combining QGSJET model of high energy hadronic interaction, are performed with this spectrum and another two spectra, HD and PD spectrum, respectively. It is shown that the new spectrum and HD can give very good results, compared with the experimental results obtained with thick Pb emulsion chambers (28 c.u.) at Mt. Kanbala (5500m a.s.l., Tibet, China), while PD spectrum can not.
The measurement errors of the deposited energy and position of neutral tracks in Barrel Shower Counter (BSC) of BESⅡ are investigated. The errors of energy and position of real data are determined by radiative Bhabha events, while the errors of Monte Carlo Data are determined by e+e－→γγ events. Then the corrections are tested by the selected ρπ sample, which shows better pull and Confidence Level distribution after the correction. The results are already applied to the kinematic fitting, which can improve the physics results at BESⅡ.
Based on the phase-space generating functional of Green function for a system with a singular higher-order Lagrangian, the generalized canonical Ward identities under the local and non-local transformation in phase space for such a system have been derived. Starting from the configuration-space generating functional for a gauge-invariant system, the generalized Ward identities were deduced under the local, non-local and global transformation, respectively. The applications to the non-Abelian Chern-Simons theories with higher derivatives were given. Some relationships among the proper vertices have been deduced, in which one does not need to carry out the integration over canonical momenta in phase-space generating functional. The Ward-Takahashi identities for BRS transformation are also obtained.
In this paper we found that the final state hadron multiplicities in Υ→3g fragmentation satisfy the same general mass dependence as in e+e－→q0q0 events. This indicates that the fragmentation of quarks and gluons to hadrons follows the same mechanism. The important character of increment of the baryon multiplicity in Υ→3g fragmentation is interpreted naturally without any other assumptions.
The importance of using a laser ion source in the on-line isotope separator, the principle of laser ion source, laser technique and the structure of hot capillary laser ion source and target chamber are introduced. A high repetition frequncy copper vapor laser and three dye lasers were used. The capillary is made of Nb with inside diameter of 1.7mm and effective length of 3cm. It was heated by 50—100A direct current and temperature of 1800—2700K can be achieved. The nuclear reaction channel used in the first on-line experiment is 50MeV/u 18O+natTa→167Yb(T1/2=17.5min). A joint operation of accelerator, on-line isotope separator and laser system has been realized. A total separation efficiency of 0.2% is obtained by comparison of the measured yield of 167Yb with the calculated yield of 167Yb by using production cross-section, beam intensity, collection time and the thickness of target. A element selectivity of 3.2 is deduced from the ratio of the corresponding peak areas of 167Yb and 167Lu in the γ spectra of laser on and laser off. A new high spin isomer with long half-life of 167Yb was found. The methods that may be used to improve the efficiency of laser ion source are discussed.
Two independent measurements of excitation functions in the dissipative collisions of 19F+93Nb have been performed at incident energies from 100 to 108 MeV in steps of 250 keV. The two measurements differed by the thickness of the target foils, 70μg/cm2 and 71μg/cm2, respectively. All the other experimental conditions, the accelerator, the incident energies and steps, the scattering chamber, the detection system, the electronics, the acquisition system and all the parameters selected in the two measurements, were kept to be identical in both experiments. The data indicate non-reproducibility of the non-self averaging oscillating yields in the two independent measurements. The indication of the non-reproducibility of the cross sections is discussed.
Calculation methods of internal conversion electron energies and their absolute intensities are briefly introduced on the basis of electronic binding energies of different shells, gamma-ray energies, internal conversion coefficients of different shells, total internal conversion coefficient and gamma-ray intensity. The application is also given by using 232Th decay as example in the text.
A self-affine analysis is performed on the jets (minijets) produced in proton-antiproton collisions at CERN SpS collider energy. The jets are identified by the "Cone algorithm". The Hurst exponents are obtained through the study on the 1-D factorial moments. A 3-D self affine analysis is performed according to these Hurst exponents. The results provide further evidence that ,the dynamical fluctuations inside jets are anisotropic in the longitudinal-transverse planes and isotropic in the transverse plane, which mimics the dynamical fluctuations in SPS fixed-target hadron-hadron collisions.
The dynamical fluctuations inside a single jet in the 2 jet events produced in e+e－ collisions at 91.2GeV have been studied using Monte Carlo method. The results show that,the anisotropy of dynamical fluctuations inside a single jet changes remarkably with the variation of the cut parameter ycut. A transition point (γpt=γφ≠γy) exists, where the dynamical fluctuations are anisotropic in the longitudinal transverse plan and isotropic in the transverse planes. It indicates that the ycut corresponding to the transition point is a physically reasonable cutting parameter for selecting jets and, meanwhile,the relative transverse momentum kt at the transition point is the scale for the determination of physical jets. This conclusion is in good agreement with the experimental fact that the third jet (gluon jet) was historically first discovered in the energy region 17—30GeV in e+e－ collisions.
Using the particle-number conserving method for treating the cranked shell model,the microscopic mechanism of the variation of the kinematic moments of inertia with rotational frequency ω for the rare-earth deformed nuclei 172,174Hf is investigated. The observed J(1) and angular momentum alignment are reproduced satisfactorily in the PNC calculation,in which no free parameters are involved. The PNC analysis shows that the difference between the variations of J(1) with ω for the high K multi-quasiparticle bands and for ground state band is mainly due to the Pauli blocking effect of high j intruder orbitals near the Fermi surface.
The trigger process of L3+Cosmics experiment at CERN is introduced briefly. Also we checked whether the settings of L3+Cosmics trigger system by simulation are correct or not and introduced a method on trigger efficiency calculation. To get trigger efficiency for μ spectrum measurement, an experimental data sample, which includes events passing the trigger set to measure the μ spectrum and not passing, is needed. Then L?3+C trigger process is simulated with these events in this sample to know how many events should pass the trigger. By checking a trigger bit recorded in the experimental data, one can know how many events passed the trigger in hardware in these simulated events. The ratio then determines the trigger efficiency for μ spectrum measurement. And the systematic error is analyzed. The results on trigger efficiency have been used to the measurement of μ spectrum.
The cavity mode method presented in this paper is used for analysis of the dispersion curves in periodical accelerating structures. At first,we computed the electromagnetic fields in a single cavity with the finite element method and construct the normalized orthogonalized short and open modes. Then it is assumed that the fields in the whole structure can be expanded linearly with these modes. Considering the Maxwell equations and the periodical boundary conditions,we get the relationship between the frequencies and the phase shifts. The parameters in the equation can be computed with the short and open modes. For the example of the disk loaded waveguide shown in this paper,it is very easy to obtain the single passband dispersion curves. The accuracy can reach 10－6. The method can also be used to compute the high order modes that meet the requirement of the single passband.
Solenoidal lenses are usually used to focus charged particle beams moving in inductive accelerators,electron linear accelerators,proton linear accelerators,low energy beam transport systems as well as some cathode ray tubes. To understand the nonlinear optical properties of solenoidal lenses,Lie algebraic methods are used in the analysis of particle trajectories in this kind of lenses,and the results of third order approximation are obtained. Because of the existence of fringing fields,one should divide the fringing field into several small segments,and apply the Lie map to each of the segments.
To take advantages of positron emission tomography(PET) in studies of physiological functions of plants,a γ-ray imaging system composed of two block detectors facing each other is under developing. The block detector consists of 10×10 lutetium oxyorthosilicate(LSO) crystals and a position sensitive photomultiplier tube(PSPMT),Hamamatsu R5900 C12,where the element size of the LSO is 1.8mm×1.8mm×10mm. The performance of LSO detector was evaluated in terms of applicability to PET. All the detector elements are clearly visualized in the position map. Energy resolution ranges from 14.5% to 22% FWHM at 511keV. Coincidence timing resolution is improved as the supply voltage of the PSPMT is increased. These measurements indicate that the LSO detector is applicable for high resolution dual block detector imaging system.
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