2003 Vol. 27, No. 8
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A data quality monitoring system for fast reconstructed event is depicted in detail for ψ(2S)data taking during 2001-2002 years' running at Beijing Spectrometer(BES Ⅱ) . In parallel with fast reconstruction of raw data, the performance and stability of BES Ⅱ subdetector can be inspected from various intuitive distributions of fast reconstructed and selected events. The system,with operation simplicity,function completeness and extension flexibility,has played and will play an important role in the quality monitoring of BES data taking.
Based on three methods of particle identification (PID) of BES,we study the identification of p and p in momentum range from 0.3 to 1.2 GeV using real particle samples of e,μ,π,K,p and p which were collected in 2-5GeV R scan,J/(ψ) and ψ′ data taking periods. The paper presents the optimized method of PID:p(p) is identified by dE/dx only if momentum below 0.6GeV,and by TOF or the combination of dE/dx and TOF for higher momentum.The PID efficiency of p, p and contamination from the other charged particles are also given.
We employ one-particle-exchange method to study D→PV decays in D→Kρ,πK , π processes. Taking a strong phase into account and considering nonfactorizable effect, we can get good results consistent with the experimental data. Nonfactorizable effect is not always large,but in some cases,this effect is necessary for accommodating the experimental data.Strong phases are approximately SU(3) flavor symmetric.
Based on the perturbative QCD predictions of gluonic distributions and branch cross section of the J/ψ decay via hadronic, electromagnetic,and radiative channels, the strict solutions of LUND area law of string fragmentation had-ronization are used to treat nonperturbative hadronic production processes, a possible description and Monte Carlo packet for the J/ψ hadronic decay are obtained. The more than 14 spectra and event shapes of the charged particles simulated by Monte Carlo generator LUARLW agree with BES data well.
We analyze the B→KK decays with the soft-gluon corrections by using the QCD light-cone sum rules(LCSR) .Although one can calculate the leading order factorization parts and the radiative corrections from hard-gluon exchanges at a, order in QCD factorization approach,it is worthwhile to estimate the nonfactorizable soft-gluon contributions from all the tree and penguin diagrams systematically. Our results show that the soft-gluon effects always decrease the branching ratios and give a few percentage corrections at most in the B→KK decays.
Using the Bonn potential plus the BR scaling parameter induced by in-medium effects,the modified relativistic mean field model proposed recently is applied to investigate the properties of neutron star. The obtained results show that the BR scaling parameter leads to the increasing of maximum masses and radii of neutron star.
Through measuring high-fold prompt γ- ray coincidence events following the spontaneous fission of 252 Cf with the Gammasphere detector array, new level scheme in the very neutron-rich odd-A 113Ru nucleus has been established. An intruder collective band based on 11/2－ level has been identified with spin up to 31/2 k and excitation energy 3.6 MeV. This band most probably originates from vh11/2. intruder orbital. Another collective band probably built on 9/2－ level is also observed. Some important characteristics of the collective bands have been systematically discussed.
Due to the contributions of the quantum vacuum to densities, the relativistic Hartree approach for finite nuclei produces a large effective nucleon mass m IMN≈0.8, which causes the spin-orbit force to be only 1/3 of the empirical value. In this work we introduce tensor couplings for the vector mesons. Consequently, the spin-orbit force is enhanced by a factor of 2 while a large effective nucleon mass remains. The nucleon spectra of shell-model states are ameliorated evidently. The predicted anti-nucleon spectra in the vacuum are deepened about 20-30MeV.
A similar method to the H-F method for particles is developed to determine the structure of the pairs. A scheme for dealing with the problem caused by the seniority mixing is also proposed. In this scheme the independent D pairs are constructed by the seniority particles introduced in this paper, and the definition of the S pair is modified in order that it can commute with the D pairs.
The σR and σ－2n have been calculated via the BUU model by using soft EOS and 0.8σCug. The density distribution which come from RMF model has been introduced to replace the normal used square-type distributions in BUU calculation. The calculated results can reproduce the experimental data well for various reaction systems. Here σ－2n is calculated as the difference between σR of halo nucleus and core nucleus, by assuming σcorr=0. It indicates that this assumption works very well in the BUU calculation.
The ground state properties of the odd-even nuclei with proton number Z=103-109 have been systematically calculated in the deformed relativistic mean-field (RMF) theory with two sets of force parameters, NL-Z2 and TMA. When comparing the calculated binding energies and alpha-decay energies with the experimental ones, we find that the theoretical results are in good agreement with the experimental data. The reliability of the RMF model for odd-even super-heavy nuclei has been tested by this comparison. The properties of some unknown nuclei are predicted and they will be useful for future theoretical and experimental researches of superheavy nuclei.
A model simulating the main aspects of avalanche growth and signal development in Resistive Plate Chambers (RPCs) is presented. The model has been used to compute the charge distribution and time distribution of Multi-gap RPCs. The comparison between model simulation and experimental results is also discussed.
The BESll Muon Counter(MUC) performance is carefully studied. The MUC cluster positions and the magnetic fields in the coil and iron york of BESⅡ are calibrated by dimuon events collected at J/ψ and ψ(2S)peak energies. With these calibration constants, the MUC raw data are re-reconstructed, the offsets of hit-positions in r -φ plane are diminished, and a better resolution is achieved. The charge-division algorithm to determine the hit position in z direction is modified, which improves the z resolution to 5cm for the first layer of MUC. All these modification will make the data analyses involving MUC information more reliable.
In electron storage ring, the distortion of closed orbit and dispersion, due to inaccuracies of magnets manufacture and misalignment, will cause a series of negative effects, such as tune-shift, distortion of optic function, decrease of dynamic aperture, and decrease of luminance et al. Previous work mainly concentrated on the correction of closed orbit, recently a method to correct orbit and dispersion simultaneously is developed to improve the performance of storage ring, and adopted by some accelerator labs. At the same time, the beam-based-alignment is adopted to let beam pass through the center of magnets instead of vacuum chamber, so the base for correction is also the center of magnets. This paper introduces the feasibility study of realizing correction of closed orbit and dispersion, by using singular value decomposition of response matrix, at Hefei Light Source storage ring. The simulation study shows that, the rms. value of closed orbit distortion is less than 0.1 mm, and dispersions at vertical plane and dispersion-free region at horizontal plane basically disappear after correction.
Electron cooling device for HIRFL-CSR main ring has been completed under the cooperation between BINP and IMP. It has three distinctive characters. Variable profile electron beam can be produced by the electron gun, the size and density distribution of electron beam can be changed. The parallelism of the magnetic field in the cooling section achieves less than 1×10－5, in this case, the r.m.s angle deviations of the magnetic field line in horizontal and vertical direction are 7.838×10 and 8.044×10－6 respectively. The electron beam loss is reduced, the vacuum condition is improved, and the instability of the electron beam is suppressed becanse of using of electrostatic bending plate in the toroid. The beam profile and density distribution were measured in the testbench. The characters of the gun and collector were investigated. The main test results are presented in this paper.
With construction of CSR and acceleration of proton at HIRFL, the existing beam handling system can not meet the requirements of nuclear physics experiments for more and more beam time. For this reason, a new beam distribution system based on time is being constructed. The new system not only deliuers beams to the new terminals for reaser-ch program of proton and heavy ion therapies, single particle effects of spaceflight electronics components and irradiration effecs of living things, but also can provide beams for CSR when physics experiments are done on the experimental terminals with the beam from both SFC and SSC. The layout, performance and beam optics calculations of the new distribution system are presented.
Higher-order modes (HOM's) excited in the Superconducting Cavity (SCC) can be damped through many ways. Microwave absorbers, HOM' s couplers, coaxial waveguides and other devices are used to achieve this aim. The recent status of the R&D on an 800MHz Prototype SCC being developed is presented in this paper. For the cavity, the HOM' s damping by absorbers is obtained with the large beam duct. A low power measurement on a prototype cavity has been carried out and the Q-values of HOM's are confirmed to be drastically reduced. Two types of ferrite as absorbers are investigated to achieve the function of damping the HOM' s. The modes we concerned focus in the range of 0.8-2.7GHz. By means of changing the parameters of the ferrite used in the cavity, a conclusion about the damping is acquired . Measurements indicate that most of the HOM' s in this range are effectively absorbed and damped at the presupposition that the basic mode is not affected. A few special modes are pointed out, which cannot be absorbed by means of absorbers because they cannot propagate out of the cavity. The two types of ferrite used in this project have similar property with the same value of B, equal to 1500Gs and the different values of e equal to 14, 16 respectively. In order to study the relation between the parameters of ferrite and the damping effect, further research will be carried out sequential- ly.
Si/Ge superlattices were grown at low temperature with modified Stranski-Krastanov (SK) MBE method. X-ray specular, off-specular reflectivity, and X-ray transverse scattering measurements were done to characterize the structure of the Ge/Si superlat-tice. The fitted roughness and the thickness of the Ge-layer indicate that Ge may diffuse into Si-layer and form the inverted trapezium or nano-scaled hut at the Si/Ge interface. The inverted trapezium extends to form islands, which can be estimated from the volume of the Ge-Si alloy in the structure. These islands can be averaged as a Ge-Si alloy sub-layer, the averaged thickness was fitted from the pure X-ray specular reflectivity. The composition of Ge in the SiGe dots was estimated as 15%-25% by X-ray specular reflectivity and by the thickness of Ge sub-layer. These results were confirmed by TEM observation.
The method of bending capillaries to limit higher energy X-ray is a possible way to select X-ray energy. Calculation and measurement using synchrotron radiation source indicated that the transmission efficiency of X-ray in "water window" through capillaries can be higher by a factor of 5 than that of X-ray with energy higher than “water window”.
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