2004 Vol. 28, No. 3
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based on a sample of 7.8×10 6 besi j/ψ events, the decay of j/ψ→ωπ +π – is studied. a low mass enhancement in the π +π – invariant mass spectrum recoiling against ω particle is clearly seen which does not come from the phase space effect and the background. according to PWa analysis, this low mass enhancement is a broad 0 ++ resonance, the σ particle. if a baeit–Winger function of constant width is used to fit the σ signal, its mass and width are 384±66 mev and 458±100 mev respectively, which correspond to the pole position at (434±78)–i(202±43) mev.
Taking the thermodynamics potential for cold dense QCD in perturbation theory to the first order in coupling constant account, we calculate the bulk viscosity of strange quark matter(SQM), and find that the result is approximately 10 2 times than that of the ideal quark gas. In comparison with quasi-particle description model, we have the same result in order of magnitude. It is useful to improve the theory prediction that to apply the result to the calculation of the rotation speed limit, which is favorable for the explanation of the observation.
Electron Cloud Instability (ECI) may take place in positron storage ring when the machine is operated with multi-bunch positron beam. According to the actual shape of the vacuum chamber in the BEPCⅡ, a program has been developed. With the code, we can calculate the electron density in the chamber with different length of antechamber and the different secondary electron yield respectively. By the simulation, the possibility to put clearing electrodes in the chamber to reduce the electron density in the central region of the chamber is investigated. The simulation provides meaningful and important results for the BEPCⅡ project and electron cloud instability research.
Synchrotron Radiation (SR) photons are generated when beam particles of BEPCⅡ undergo the acceleration in magnetic fields of dipoles and quadrupoles. Three programs, SRGEN, SRSIM and EGS are used to simulate the SR spectra, power deposition and the background of SR in detectors of BESⅢ due to the interaction of SR with the material of beam pipe etc.
A Monte Carlo simulation on production characteristics of high energy family events observed with Mt. Kanbala emulsion chambers is made based on hadronic interaction models QGSJET and DPMJET with program CORSIKA which is commonly used in the simulations of EAS experiments. The production efficiency of family events for different primary particles and its relationship with primary energies are given. The distributions of lateral spreads, numbers of showers, total visible energies of the family events and their corresponding average values got from simulations are systematically compared with those of the experiment. It shows that their results are consistent basically. Additionally, family events from both simulations and experiment have the similar tendency of energy concentration.
We study ρ-ω interference by analyzing J/ψ→π+π-π0π0. PDG-2002 data on J/ψ decays into PP and PV (P denotes pseudoscalar mesons; V, vector mesons) are used to fit a generic model which describes the J/ψ decays. From the fits, we obtain anomalously large branching ratio Br(ρ0→π+π-π0)≈10－3－10－2. A theoretical analysis for it is also provided, and the prediction is in good agreement with the anomalously large Br(ρ0→π+π-π0). By the fit, we also get the η-η′ mixing angle θ= -19.68°±1.49° and the constituent quark mass ratio mu/ms≈0.6 which are all reasonable.
In this paper, we investigate the instanton effects to the mass of 0++ glueball by QCD sum rule approach. The instantons are assummed to be free from each other and be with definite density varying with their sizes. We find the upper bound of mass of the 0 ++ glueball is 1.3GeV and very possibly the mass can be as low as 1GeV. Besides, the instanton effects greatly improve the stability of the sum rule and overtake the contribution of quarks and gluons condensate. The centre size of instantons at 1/3fm can give the stablest sum rule.
In this paper gives a general expression of matter density ρ that is relative to cosmological different inflations, and a new general solution of the cosmological scale factor is derived out. We find that the cosmological scale factor has a composite function form of exponent inflation if the cosmological constant is positive, and the factor is a composite function of cosine if the cosmological constant is negative. The cosmological scale factor returns to the usual solved solutions when the parameters in the general density function are taken as some special values. Furthermore, a new dynamical parameter C that affects the inflation of the cosmology is found.
We study the action of volume operator on spin network states with n-valent vertices. In particular, the recoupling matrices are re-derived by means of a graphic formulation.
n-and 2n-transfer reaction products 10Be and 11Be at large c.m. angles were measued in a specially designed set-up for the bombardment of 9Be by 6He at 150MeV. In total 371 10Be and 511Be events, corresponding to 1n-and 2n-transfer respectively were identified. The experimental differential cross-sections obtained are 0.11±0.02mb/sr(θcm≈137.4°) and 1.0±0.7μb/sr(θcm≈133.4°) for 1n- and 2n-transfer, respectively. Such results indicate that the differential cross-section of 1n-transfer is about 100 times higher than that of 2n-transfer at large c.m. angle in the reaction studied. Calculation using zero range Distorted Wave Born Approximation(DWBA) for 6He under 5He-n and α-2n two-cluster models are performed and discussed.
Excited states of 134Ba, populated up to medium and high spins via the heavy-ion induced 128Te(10B,1p3n)134Ba reaction at 46 MeV beam energy, have been studied using in-beam γ-ray spectroscopy techniques. Nine anti-Compton HPGe detectors were employed for the measurements of γ-γ-t coincidences. Based on the results of the γ-γ coincidence relationships, relative intensities and ADO ratios, a level scheme of 134Ba has been established. Comparing with the systemic features of the negative bands of N=78 isotones, the 11－ state at the excitation energy of 4142keV, is analogous to the one in 136Ce.
Several mechanisms have been proposed for the signature inversion in the structure of A≈80 odd-odd nuclei, but the theoretical calculations have not been conclusive. In this work, the angular momentum projected shell model (PSM) is applied to the nuclei 80,82Rb. The results of theoretical calculations about the positive-parity yrast band with configuration πg9/2⊙νg9/2 and the negative-parity yrast band with configuration π(p1/2 or p3/2 or f5/2)⊙νg9/2 are compared with experimental data, especially, the mechanism of the signature inversion in the positive-parity yrast band is discussed. The interpretation within the projected shell model shows that the signature inversion displayed in the positive-parity yrast band in these nuclei is a signal of a substantial quadrupole shape change with increasing spin where the nucleus evolves from a prolate shape at low spin through a triaxial shape to an oblate shape at high spin. In addition, we also specify the nuclear shape for these two bands in these two unclei, respectively.
The E0 transitions in the even-even 102—110Pd isotopes are studied in the U(5)-SU(3) and the U(5)-O(6) transition in the framework of the interacting boson model respectively. It is found that the structure of the isotopes can be better described by the U(5)-SU(3).
Within the spin-dependent Brueckner-Hartree-Fock framework, the equation of state of the spin-polarized nuclear matter has been investigated by adopting the realistic nucleon-nucleon interaction AV18 supplemented with a microscopic three-body force. The related physical quantities such as the Landau parameters G0 in spin channel and G′0 in spin-isospin channel, have been calculated. The three-body force effects have been studied and stressed with a special attention. It is shown that in the Brueckner-Hartree-Fock framework the predicted energy per particle of spin-polarized nuclear matter versus the neutron and proton spin-polarization parameters fulfills a quadratic law in the whole range of spin-polarization. At the empirical saturation density, the calculated Landau parameter G′0 is 1.22 and 1.28 respectively for the two-cases with and without including the three-body force, both are in agreement with its experimental value. Both the Landau parameters G0 and G′0 are positive in the density region up to ρ=0.5fm－3 and increase monotonically as increasing density so that no any evidence is found for a spontaneous transition to a ferromagnetic state in nuclear matter. The three-body force effect is to strongly increase the Landau parameters G0 and G′0 at high densities, making the nuclear matter at high densities more stable against spin and spin-isospin fluctuations. The obtained Landau parameters G0 and G′0 together with their density dependences may serve as constraints on the spin-spin parts and spin-isospin dependent parts of the phenomenological Skyrme and Skyrme-like interactions.
In this paper, we presented a nuclear density empicical formula of the nucleus, where we have established the connection between the nuclear density and the mean binding energy in nucleus. By using the formula, we can get the nuclear density for various nuclei with A≥12. By means of the nuclear density model, we calculate the nuclear effect function RA1/A2(x,Q2). The calculated results are in good agreement with NMC experimental data.
The β-NMR and β-NQR spectrometer has been established for the first time in China. The lifetime, magnetic moment and polarization of 12B were measured with it. The experimental results show the reliability of this newly established β-NMR and β-NQR spectrometer.
The 3D distribution of electric field in GEM (Gas Electron Multiplier) electrode is calculated based on the finite element method. The transmissivity of electric field lines in four types of GEM are obtained, these are 33.12%,34 85%,40.70%, and 16.70% for double-conical, cylindrical, single-conical and inverse-conical electrodes respectively. The three dimensional calculation of electric field in GEM agrees with the experimental data better than the two dimensional calculation.
For the use of narrow E-beam lithography, the Cockcroft-Walton accelerator is often required. Electrons from the gun will be accelerated by a high voltage and reached a target via electric focusing lenses and bends. To have a high quality narrow E-beam, the noise suppression for the accelerating voltage is one of the key issues. It is verified by our experiments on SDS-3 e-beam lithography machine. The system supplies analog current to the accelerator's tuning circuit, which is proportional to the input voltage. The compensation amplifier consists of main amplifier and an auxiliary one. The auxiliary amplifier reduces input offset drift on output of the main one. The general design project of a combined regulation type for the Cockcroft-Walton accelerator was described. The key technical measures for obtaining a high accelerating stability were introduced. By filtering the noise from the final output of the machine, an output voltage with high stability was obtained, and hence the pattern quality and the line resolution of the mask were improved.
This paper addresses the output characteristics of real electron bunches accelerated with ultra-intense laser pulse in vacuum by the capture and acceleration scenario (CAS) scheme. It shows that there exist three kinds of electrons' trajectories after the interaction between electron bunch and laser pulse, namely pass-by, inelastic scattering and CAS. Normally, as the size of an electron bunch is much larger than that of a tightly focused and compressed laser pulse, only those electrons located in the central region of the incident bunch can be accelerated to high energy. For a high intensity laser (～1021W/cm2) and an electron bunch (～108 electrons), the maximum electron energy gain from the laser field can be more than 450MeV, and the number of CAS electrons can reach to 104-105. These results demonstrate that CAS is promising to become a novel mechanism of vacuum laser accelerators.
In order to get some experience to build a new modulator for DESY TESLA Test Facility (TTF), a 150V direct switch long pulse modulator has been designed. Compared to the modulator solution currently used at TTF, the new proposed one has some advantages. Part of the simulation calculation of the 150V direct switch modulator is given in this paper. At the same time, a 150V modulator model was constructed and measured. The test results show that the output voltage flat-top ripple is only ±0.53%.
To investigate the higher order mode (HOM) damping in the BEPCⅡ superconducting cavity (SC) when using HOM absorbers, simulations have been done for changing the position and the length as well as the thickness of ferrite of HOM damper, and for different positions and angles of taper. The optimized values under which the HOM impedance of the BEPCⅡ SC cavity will be trapped in the impedance threshold of the BEPCⅡ collider have been found. For verifying the simulation result mentioned above, HOM measurements on the BEPCⅡ model cavity have been made, and the satisfied results for HOM damping are obtained. The distribution and magnitude of some potentially dangerous higher order modes have been found, which are basically consistent with the simulations.
B9B is a soft X-ray beamline in Beijing Synchrotron Radiation Laboratory, the photon energy range is 10-1000eV, photon energy of the low energy branch is from 10-60eV, mainly for angle resolved photoemission spectrum. Within years operation, some experiments were limited by the poor coumt-rate. This article analyzed the shortcomings on the design of the low energy branch, introduced a new scheme of beamline upgrade which need to change two focusing mirrors, meanwhile the mirror parameters was calculated and tracing results of the new beamline was presented. During SR beam time, performance of the beamline was tested after the improvement work, which shows a much more smaller focused image on sample position, and meanwhile the count-rate of experiments with upgraded are increased by more than one order. The beamline is put into use after the upgrade.
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