2004 Vol. 28, No. 04
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Evidence of ψ(3770) decays to a non-DD final state is observed. A total of 6.8±3.0 ψ(3770)→J/ψ→π+π— events are obtained from a data sample of 8.0±0.5 pb-1 taken at center-of-mass energies around 3.773GeV using the BES-Ⅱ detector at the BEPC. The branching fraction is determined to be BF(ψ(3770)→J/ψ→π+π—)=(0.59±0.26±0.16)%, corresponding to the partial width of Γ(ψ(3770)→J/ψπ+π—)=(139±61±41)keV.
BAI Jing-Zhi. First Evidence of ψ(3770) Hadronic Transition to J/ψπ+π—[J]. Chinese Physics C, 2004, 28(04): 325-331.
New isotope 265Bh(Z=107) was produced in bombardment of an 243Am target with 135MeV 26Mg ions at HIRFL. Identification was made by observation of correlated α particle decays between the new isotope 265Bh and its 261Db and 257Lr daughters with four pairs of detectors. A total of 8 correlated decay events of 265Bh and 4 decay events of 264Bh were identified. 265Bh decays with a 0.94+0.70-0.31s half-life by emission of α particle with an average energy of (9.24±0.05)MeV.
In the process of design and research of BES Ⅲ crystal calorimeter, we made a detailed Monte Carlo study for the performance of BES Ⅲ CsI crystal calorimeter on the basis of the detection cell of 7×7 CsI matrix. Results are presented on incoherent noise, on energy linearity, on uniformity of the crystal light output, on position dependence. Those results show that the energy resolution of the 5×5 matrix sum is about 2.1% for 1 GeV photon and the best energy resolution of the lower energy photon is obtained with the energy threshold of 2.5 σnoise. The energy deposit in the matrix decreases by about 1% and the energy resolution degrades by about 0.3% when 800MeV photons are injected in the gap region between two crystals. The average position resolution is about 6.3 mm at 800 MeV.
We improve O(p4) calculation in U(2)L×U(2)R chiral theory of mesons by resummation calculation for vector mesons physics and restudy decay ρ→ππ. We obtain a complete and compact expression for fρππ(p2) (up to O(p∞)), from which an important non-perturbative conclusion is drawn from convergence and unitarity consideration.
We consider the rare top quark decays in the framework of topcolorassisted technicolor (TC2) model. We find that the contributions of top-pions and top-Higgs predicted by the TC2 model can enhance the SM branching ratios by as much as 6—9 orders of magnitude. i.e., in the most case, the orders of magnitude of branching ratios are Br(t→cg)～10－5, Br(t→cZ)～10－5, Br(t→cγ)～10－7. With the reasonable values of the parameters in TC2 model, such rare top quark decays may be testable in the future experiments. So, rare top quark decays provide us a unique way to test TC2 model.
J/ψ and ψ′ radiative decays to mesons are a good place to look for glueballs, hybrids and for extracting gg-q couplings. Abundant J/ψ and ψ′ events have been collected at the Beijing Electron Positron Collider (BEPC). More data will be collected at upgraded BEPC and CLEO-c. Here we first provide explicit formulae for the angular distribution of photon of the ψ radiative decays in the covariant tensor formalism. Then we discuss helicity formalism of the angular distribution of the ψ radiative decays to two pseudoscalar mesons, and its relation to the covariant tensor formalism.
In this paper, we construct the Lax pair of classical Lie algebra Dr according to the characteristic of its root system, and get a family of integrable generalizations of Toda mechanics (labeled by a pair of ordered integers (m,n), m,n denote the order of positive and negative roots respectively). We aiso provide the explicit equations of motion, the Hamiltonian and the Poission brackets corresponding to the case of m,n≤3.
The superposition states, which are composed of the generalized q-coherent states of the non-harmonic oscillator, are presented. The quantum statistical properties of these states are studied. Then the influence of the superposition phase δ and the deformation parameter q on these nonclassical properties are discussed. It is shown that the superposition states exhibit higher-order (order of odd number) squeezing effect and antibunching effect respectively. When the superposition phase δ is taken values approach to 0 or π/2, these results approach the properties of the even or odd generalized q-coherent states of the non-harmonic oscillator. Especially, the effects are influenced by the parameter q. When the values of q is taken departure from 1 greatly, the nonclassical properties are more evidently.
The level structure of 60—66Zn isotopes is studied within the framework of interacting boson model-3 (IBM-3). The mixed symmetry states are investigated in these nuclei by analyzing the wave functions. The isospin excitation states are identified for 60Zn (N=Z) nucleus. The calculated energy levels and transition probabilities are compared with available experimental data. The results obtained and the values of parameters used in this calculation indicated that the Zn isotopes are in the transition from vibrational to γ-unstable nuclei.
Taking into account of inelastic scattering process, such as ionization, excitation et al., a Monte Carlo track structure model of the proton and α particle in water has been described. In the simulation, the energy range of proton and α particle is about 0.3—5MeV/u. The cutoff energy of secondary energy electron is taken as 1eV. Tracks were analyzed to provide confirmation on the reliability of the code and the information on physical parameters, such as range, radial dose profiles. Our Model calculation shows the good agreement with the experimental data.
Based on the QHD-1 field equation, the dielectric constant of nuclear matter with the ωNN interaction has been obtained in the framework of kinetic theory. Furthermore, the characters and physical background of the dielectric constant at high temperature is analyzed in detail.
The evolution and dilepton production of a chemically equilibrating quark-gluon plasma system at finite baryon density have been studied. It was found that due to the increase of the quark phase life-time with increasing initial quark chemical potential, and other factors like higher initial temperature, larger gluon density and gluon fusion or quark annihilation cross section, thermal charmed quarks provide a dominant contribution to dilepton yield. This results in a significant enhancement of intermediate mass dilepton production.
A density dependent relativistic mean field theory is used to investigate the effect of nuclear matter on σ, ω, ρ and π meson masses. The obtained results have been compared with those given by the linear Walecka model, a nonlinear Walecka model with the parameter set TM1, and the TW model. It has been shown that the overall trends predicted by the different models are quite similar. The effective meson masses decrease with the increasing of nuclear matter density in the lower density region, while the effective σ, π meson masses begin to increase with the density of nuclear matter, and the decreasing behaviors for the effective ω, ρ meson masses tend to become slower in the higher density region. The influence of asymmetric parameter α on the effective meson mass is considerably small, moreover, the nonlinear self-interaction terms in the parameter set TM1 and the many-body coupling (σπ)2 are important to the effective π meson mass.
We used LUCIAE3.0 model to simulate the Pb+Pb and C+C in SPS energy. The heat capacity was then extracted from event by event temperature fluctuation. It is found that the heat capacity per hadron multiplicity decreases with the increasing of beam energy and impact parameter for a given reaction system. While the hadron mass increases, the heat capacity per hadron multiplicity rises. In addition, we found that, for a given hadron, the heat capacity per hadron multiplicity is almost the same regardless the reaction system. Some discussions were also given.
Based on the isospin dependent quantum molecular dynamics model we investigated the isospin effects of isospin fractionation (N/Z)gas/(N/Z)liq from the neutron-proton ratio of colliding system and impact parameter. Here (N/Z)gasand (N/Z)liq is the neutron-proton ratio of nucleon emission for gas phase and that of fragment emission for liquid phase, respectively. Our results show that the (N/Z)gas/(N/Z)liq increases with the neutron-proton ratio of colliding systems when the system mass, incident energy and impact parameters are fixed. For the neutron-rich systems, the (N/Z)gas/(N/Z)liq depends sensitively to the form of symmetry potential and weakly on the isospin effect of the in-medium nucleon-nucleon cross section; For the neutron-poor colliding system, however, the (N/Z)gas/(N/Z)liq is not sensitive to both the form of symmetry potential and the isospin effect of the in-medium nucleon-nucleon cross section. We also found that the dependence of (N/Z)gas/(N/Z)liq on the impact parameter is not obvious. Detailed discussion and explanation for leading to these results are presented in the paper. According to these results, we propose that (N/Z)gas/(N/Z)liq can be directly compared with the experimental data to get the information about symmetry potential.
Micro-strip Gas Chamber (MSGC) used as a position sensitive detector has perfect performances in the detection of nuclear irradiations. However, it encounters a severe problem, that is, positive charge accumulation which can be avoided by reducing the surface resistivity of insulating substrate. So, diamond-like carbon (DLC) film is coated on D263 glass to modify its electrical properties as substrate for MSGC. Raman spectroscopy demonstrates that DLC film is of sp3(σ bonding) and sp2 bonding (π bonding), and therefore it is a type of electronically conducting material. It also reveals that the film deposited on D263 glass possesses very large of sp3 content and consequently is a high quality DLC film. I-V plots indicate that samples with DLC film enjoy very steady and suitable resistivities in the range of 109—1012Ω·cm. C-F characteristics also show that samples coated by DLC film have low and stable capacitance with frequency. These excellent performances of the new material, DLC film/D263 glass, meet the optimum requirements of MSGC. DLC film/D263 glass used as the substrate of MSGC should effectively avoid the charge pile-up effect and substrate instability and then improve its performances.
A kind of double-GEM gas detector which can be used for X-ray imaging and charged particle tracking detection, is studied. The effective gain and stability properties of the double-GEM gas detector are measured by high intensive X-ray source (Cu-target, 8.9keV). The results show that the effective gain of the GEM gas detector is up to 104, and the detector has a good stability properties comparing with the MWPC under the X-ray rate of 10 5 Hz·mm－2.
A method was developed for efficiency calibration of large area neutron detectors based on γ-n coincidence and time-of-flight techniques using a 241Am-9Be neutron source. The detector efficiency was also calculated by a Monte Carlo code and compared to the experimental results.
YBJ-ARGO experiment is designed to detect small size air showers at an energy threshold of～100GeV using a full coverage RPC array. High detector efficiency, good time resolution (～1ns) and low strip multiplicity (～1.2) are needed to meet the experiment requirements. Performance of RPC, including the above mentioned detector parameters together with the RPC current, is studied at high altitude (4300m a.s.l.) with a normal RPC gas mixture, under which high strip and hit multiplicity effect is observed due to the float of the CHAMBER mass reference which creates concomitant strip multiplicity when a large streamer develops in the CHAMBER. By adding SF6 component into the gas mixture to limit the streamer development together with adjusting the pull-down threshold of the signal-receiving system, the mass-reference-float effect is effectively eliminated, thus achieving lower strip multiplicity and lower working current under the same working high voltage.
In order to improve the accumulation of the injected beam, it is necessary to restrain β-oscillation because of injection system error. This paper systematically introduces the design principle and circuit of the feedback system for the injected β-oscillation suppression of HLS. It also provides the preliminary experimental results. As the proof of the theory and pre-study, we use a relatively simple analog filter and phase shifter to agitate the Kicker course, which causes the β-oscillation, and get the feedback, from which we see the obvious suppression effect. All of these are the foundation of feedback system of bunch-by-bunch and lower frequency in the future, which are for the research of transverse beam & lognitudinal beam instability.
Using the Monte Carlo code MCNP4B, skyshine of 9MeV electron linear accelerator was calculated with a multi-step method combining the split and roulette variance reduction technique. Dose distribution of the skyshine was measured around the accelerator room. Results of the Monte Carlo simulation, empirical formulas and dosimetric measurement were compared and analyzed. In conclusion, the dosimetric measurement agrees with the results computed by Monte Carlo method reasonably, but deviates with computational results from empirical formulas. It shows that Monte Carlo method is a good way to analyze skyshine.
The Palmer cooling is always used for large dispersion momentum cooling in storage ring. So it will be used during the stripping injection of HIRFL-CSRm. Here the Palmer cooling is described. The optimum cooling time, optimum gain and optimum cooling bandwidth are obtained in the simulation with Palmer method. Using the Fokker-Planck equation, the particle distribution with respect to the momentum dispersion is also obtained numerically during the stochastic cooling process. This is useful for analysis of experimental data and for design of the cooling system, i.e, optimization of the system passband and gain, specification of accuracy of the signal transmission, etc.
We present the layout of Peking University SASE FEL facility (PKU-FEL) to be driven by a superconducting accelerator currently under construction. PKU-FEL is a test facility to study the physical and technical issues of single pass SASE FEL. The study of theoretical model and numerical simulation for the design of PKU-FEL is described. Optimized hybrid planar undulator parameter are got in this paper. The influences of electron beam properties including peak current, emittance, energy spread and pulse duration are discussed. With the optimized parameter, PKU FEL is designed to get saturation at 7 micron with a 5-meter long hybrid undulator.
The formulas for the pulse length and number of photons of X-ray based on linear Thomson scattering of intense laser beam by highly relativistic electron beam at arbitrary interaction angles are deduced. The effects of position and synchronization error are calculated from these results. Some other nonideal factors, such as energy spread, beam emittance, are also discussed.
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