2006 Vol. 30, No. 5
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An Object-Oriented Monte Carlo program BOOST based on Geant4 toolkit has been developed for BESⅢ detector simulation. It describes the full BESⅢ detector geometry and records hit information in sub-detectors. BOOST outputs raw data and MC truth information in an ASCII file for reconstruction and physics analysis, and preliminary results show that BOOST simulation is reasonable.
Using Monte Carlo simulation, reconstruction of photon conversions is studied, and the detection efficiency and energy resolution as a function of photon energy are obtained.The dE/dx correction for the electrons from photon conversions and the energy scale for the photons are calibrated with BESⅡ data. An improved Crystal Ball function describes well the energy distribution of the photons. Photon energy resolutions in the range from 2.3 to 3.8MeV are found for the photons with energy from 100 to 260MeV at the BESⅡ~detector.
Space coordinates may become noncommutative near the string scale. In this paper, we give a representation of the noncommutative coordinates and noncommutative momenta. We then apply this representation to compute the eigen energy splitting of the isotropic harmonic oscillator in two and three dimensional noncommutative spaces.
The imaging test setup for the Hard X-ray Modulation Telescope (HXMT) mission was built to give verification of detector performance and the imaging properties of HXMT. It consists of 18 slat-collimated NaI(Tl)/CsI(Na) phoswich detectors with a total collective area of 5000cm2. Several experiments were implemented with radioactive sources 15m away from the detector plane. We obtained a point-source location accuracy of 2' and an angular resolution of $<$5' using direct demodulation method.
The scaled factorial moments of slow particles produced in 16O-Em at 3.7A GeV have been calculated. It is obtained that the intermittency exponent increases with increasing moment order and decreases with increasing target mass, the anomalous fractal dimension dq decreases with increasing multiplicity for each order of the moment. This behavior of anomalous dimensions dq reveals a self-similar cascade mechanism in the case of the interactions of 16O-Em at 3.7A GeV.
High-spin Level structure of 188Tl has been studied via 157Gd(35Cl,4n) fusion-evaporation reaction at beam energy of 170MeV. A rotational band built on the πh9/2×υi13/2 configuration with oblate deformation has been established. Spin values have been proposed to the πh9/2×υi13/2 oblate band based on the similarities between the oblate band of 188Tl and those in odd-odd 190—200Tl. With the spin assignments, the low-spin signature inversion has been revealed for the πh9/2×υi13/2 oblate band of 188Tl. The low-spin signature inversion can be interpreted qualitatively in the framework of the quasi-particles plus rotor model including a J dependent p-n residual interaction.
The mass of Θ+ in the qq-q-qq configuration is calculated by using a potential composed by a Coulomb potential originated from the One Gluon Exchange (OGE) and a double Y-mode confining potential extracted from the flux tube model. It is shown that the mass of the negative parity state of Θ+ is 1.935GeV, which is more than 300MeV higher than the reported experimental value of 1.540GeV. While the positive parity state of Θ+ has a mass of 2.082GeV, which is consistent with the result from the Lattice Quantum Chromodynamics (LQCD) calculation. With these masses, the reported Θ+(1540) cannot be confirmed as a pentaquark state.
The effects of iso-scalar ω tensor coupling on spin-orbit splittings are studied in the framework of the Relativistic Mean Field theory. Taking 208Pb as an example, the influence of iso-scalar ω tensor coupling on nuclear mean-field potentials, σ-, ω- and ρ-meson fields, spin-orbit potentials, spin-orbit splittings and the single-particle level structure near the Fermi level are presented. It is found that the tensor term mainly changes the nuclear mean-field potential at the surface. A larger tensor coupling term will lead to stronger spin-orbit potential and larger spin-orbit splitting in the single particle level, which will change the single particle level structure, remove the traditional magic numbers and produce new ones.
In the deeply inelastic e-A scattering, the gluon radiation induced by multiple scattering will lead to medium modification of the parton fragmentation functions and also associate with the energy loss of the leading quark. To obtain the hard partonic part of quark-gluon double scattering, one can do a complete calculation within the framework of generalized factorization in perturbative QCD. In another way one can utilize the approach of helicity amplitude approximation(HAA) to calculate the amplitude of gluon radiation. However, the two methods are both complicated and tedious. In this paper, we will introduce a new approach which enables one to calculate easily the amplitude for gluon radiation in multiple scattering. The final results obtained by using our new approach agree exactly with the complete calculation in perturbative QCD.
The effect of deformation on pre-scission particle emission of three heavy isobaric systems, 200Ag, 200Tl, 200Bi, and light isobaric systems, 110Pd, 110In, 110Te, are investigated by the combined dynamical statistical model and the statistical models, respectively. The calculated results show that deformation has an effect on the isospin dependence of particle emission, but it does not change the dependence of different particle emission on the isospin of the systems. Possible reasons are discussed.
By means of the improved quantum molecular dynamics model, the incident energy dependent dynamical fusion potential barriers for heavy nucleus reaction systems are investigated. It is found that with decrease of incident energy the lowest dynamic barrier is obtained which approaches to the adiabatic static barrier and with increase of the incident energy the dynamic barrier goes up to the diabatic static barrier. Based on the dynamical study a microscopic understanding of the extra-push in fusion reactions of heavy systems and a new explanation of tunneling process for the fusion at the incident energy below the static and above the lowest dynamic barrier are presented. In order to understand the energy dependence of the dynamical barrier we also pay a great attention to study the neck formation and shape deformation during the dynamic lowering of the barrier.
In virtue of the simple physical picture of quark combination model, we determine the dependence of anti-particle to particle ratios on the mean production probability of anti-quarks and quarks. The ratios of various anti-particle to particle at relativistic heavy ion collisions are calculated without any additional assumption, which are consistent with the experiment results of the Au+Au collision at √SNN=130GeV measured by STAR collaboration at RHIC. These results provide a basis for further studies of particles ratios in relativistic heavy ion collisions.
We present the results of an aging test on two six-gap multi-gap resistive plate chambers (MRPC) designed for the RHIC-STAR TOF system. The test was carried out with a 100mCi 60Co γ ray source. MRPCs were irradiated by different dose rates of the source. One module has been irradiated by high dose rate (2.87×10－2Gy/h)for 24h. Great degradation of noise rate, dark current and other main specifications can be seen. Another module has been irradiated for 530h by relative lower dose rate of 5.31×10－4Gy/h and no any significant performance degradation is observed. The goal of the test is to study the performance varaition of the detector by the large irradiation dose expected in the experiment in several years of operation.
The Endcap TOF (ETOF) of Beijing Spectrometer(BESⅢ) is consisted of 2×48 pieces of trapezoidal scintillator. Its main physics goal is to realize 2σ π/k separation at momentum up to 0.8GeV/c, and to reach the intrinsic time resolution of 80ps. In this paper, the properties of photomultiplier tube(R5924) and plastic scintillators (BC404, BC408, EJ204) are studied, a ETOF module with different wrappings is tested with the beam of 800MeV electron at IHEP. The results show that the time resolution of an ETOF module using scintillator BC404 or EJ204 is below 80ps which includes the electronic fluctuation. The ESR wrapping can efficiently enhance the amplitude of the output pulse and improve the performance of the TOF detector.
Motivation of the Touschek backgrounds study is introduced. Also introduced are the theory and modeling methods of the Touschek effect. The Touschek backgrounds of the main detectors of the BESⅢ are studied in detail using the self-reprogrammed general simulation tools. Comparison of the beam lifetime between the simulated and calculated ones shows that the simulations are reasonable and the results are meaningful. Results of the detectors' backgrounds show that the Touschek backgrounds won't affect the normal run of the future BESⅢ and won't damage the main detectors.
In modern high energy accelerators, with the increase of charge in a bunch or a bunch train, the induced transient beam loading voltages become higher and higher when the beams pass through the standing wave cavities. But in the usual analysis, people usually pay more attention to the steady state instead of the transient state beam loading. In this paper, the transient nature of beam loading and the cavity's frequency changing behavior seen by the RF power generator are studied, and then the optimum detuning conditions in two cases are derived. In the first case, the resonant cavity's frequency can be tuned to meet the in-phase condition between the RF power enerator current and the cavity voltage during the passage of beams. While in the second case, only few bunches in the bunch train and the cavity's resonant frequency is fixed during the passage of the bunch train. At last, the beam loading effects in the prebuncher of BEPCⅡ pre-injector and the two SHBs of BEPCⅡ futurepre-injector are studied.
The principle of particle coupling between horizontal and vertical directions in solenoid is presented. Further more, the method of decoupling can be obtained by using the coupling dynamic equations. 5000 particles are tracked under three conditions: CSRm doesn't contain solenoids, contains main solenoid and toroids, contains compensating solenoids. The results of the particle trace calculations show that the particles coupling between horizontal and vertical is very serious because of the existence of solenoids, and lots of particals are lost. Another two solenoids which locate in the fit place can be used to decrease the coupling intensation. The method is proved to be useful by the trace calculations.
The new electron gun system for the BEPCⅡ was tested on the test bench in July, 2004, and has been put into operation since Nov. 2004. This article describes the experiment results and operation status of this new system. The design current of the gun is 10A for the pulse length of 1ns single bunch or two bunches with repetition rate of 50Hz. The gun is operated with a pulsed high voltage power supply which can provide up to 200kV high voltage. Some important correlation curves are obtained during the experiment. Two-bunch operation is available and some elementary tests have been performed. The measurement results including beam current and beam emittance show that the simulations performed during design stage are roughly consistent with the practice. The practical operation shows that the design and manufacture are basically successful.
This paper is involved in multi-pulsed emission characteristics of some cathodes while generating intensive relativistic electron beams. Research results indicate that the velvet, the carbon fiber and the dispenser cathode all have the ability to generate a few kilo-ampere multi-pulsed beams with brightness better than 3×107A/(m.rad)2. And some new cathodes such as carbon nano-tubes and nano-diamond film also can generate a few kilo-ampere multi-pulsed electron beams. Because of the cold field emission, the beams generated by the carbon nano-tubes and the nano-diamond film are expected to be higher brightness. Some experimental results of above cathodes are present and some suggestion for farther work is also proposed.
The interface effect of semiconductor InSb nanoparticles (NPs) embedded in a-SiO2 matrix was investigated via multi-scattering XANES simulations. The results show that the white line increase and broadening to higher energies of InSb NPs embedded in a-SiO2 host matrix are mainly due to the interaction of InSb NPs and a-SiO2 matrix.It can be interpreted as both a local single-site effect on μ0(E) due to the effect of a-SiO2 matrix on Sb intra-atomic potential and the increase in 5p-hole population due to 5p-electron depletion in Sb for the InSb NPs embedded in SiO2 matrix. On the other hand, our result reveals evidently that it is not reasonable to estimate the 5p-hole counts only according to the intensity of the white line due to the interface effect of nanoparticles.
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