2007 Vol. 31, No. 2
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Instantons can induce characteristic events in deep-inelastic e+p scattering. Such effects are expected to become sizable in QCD. In the present paper QCD-instanton induced events are modelled by the Monte Carlo generator QCDINS. Different methods to reconstruct the instanton part and the current jet are tried in the boson-gluon fusion events of deep-inelastic e+p scattering with instantons as background, using QCDINS Monte Carlo event generator. A comparison among these methods are performed and an optimum method is proposed, which can reconstruct well the energies of current jet and instanton as well as the mass of instanton. The proposed method will be useful in the Monte Carlo study of the physical properties of instanton, and can serve as a reference in the experimental identification of instanton.
The previous experiments which provide information on the ψ(3770) to non-DD decays are reviewed. Three approaches of searching for the non-DD decays are discussed in detail. It is also pointed out that the search for the non-DD decays of the ψ(3770) is very important for the understanding of the dynamics of charmonium decays.
From the simple physical picture of quark combination model, we obtain the generate probabilities of various particles and relative ration in e+e－→q0q0→h′s process, and find that the relationship between the ration of strange hadron to unstrange hadron γ and the strangeness suppression factor λ. Our results can be used to explain particle ration enhancement observed in experiments without assumption of strangeness suppression factor enhancement.
In the framework of topcolor assisted technicolor (TC2) model, we calculate the contributions of cross section from the pseudo Goldstone bosons and new gauge bosons to e+e－ →bb. We find that, within reasonable ranges of the parameters, the corrections arising from technipions and new gauge bosons are negligibly small; and the top pions afford dominate contribution, the maxim cross section corrections can reach 43% with the c.m. energy √s=500GeV; whereas in case of √s=1500GeV, the maxim cross section relative corrections is only 3.1%. It might open a window to detect topcolor assisted technicolor model in the experiment of next generation linear collider.
In terms of the isospin-dependent quantum molecular dynamics model (IQMD), important isospin effect in the halo-neutron nucleus induced reaction mechanism is investigated, and consequently, the symmetrical potential form is extracted in the intermediate energy heavy ion collision. Because the interactive potential and in-medium nucleon-nucleon (N-N) cross section in the IQMD model sensitively depend on the density distribution of the colliding system, this type of study is much more based on the extended density distribution with a looser inner nuclear structure of the halo-neutron nucleus. Such a density distribution includes averaged characteristics of the isospin effect of the reaction mechanism and the looser inner nuclear structure. In order to understand clearly the isospin effect of the halo-neutron nucleus induced reaction mechanism, the effects caused by the neutron-halo nucleus and by the stable nucleus with the same mass are compared under the same condition of the incident channel. It is found that in the concerned beam energy region, the ratio of the emitted neutrons and protons and the ratio of the isospin fractionations in the neutron-halo nucleus case are considerably larger than those in the stable nucleus case. Therefore, the information of the symmetry potential in the heavy ion collision can be extracted through such a procedure.
By using the real part of the optical potential obtained in the folding model calculation and the imaginary part of the optical potential of Koning and Delaroche, the data of the proton elastic scattering off 30—40S are calculated and analyzed. By introducing the one-body density matrix of nuclear shell model with Woods-Saxon potential, the local approximation which is usually used in the folding model can be eliminated. The effects of the local approximation on the folding potential and the cross sections of elastic scattering are analyzed. The calculated results are compared with those of the folding model and JLM model.
Thermalization of quark matter and antiquark matter can be influenced by the scattering processes from quark-quark-antiquark to quark-quark-antiquark in quark-gluon matter, and the scattering amplitudes of such processes are the basis of studying thermalization. According to the perturbative QCD, a Fortran code for deriving individual squared amplitudes of all the qqq→qqq scattering Feynman diagrams and interference terms between different diagrams at order α4s is written and corresponding squared amplitudes and interference terms are derived.
Pseudospin symmetry and spin symmetry in Sn isotopes from the proton drip line to the neutron drip line are investigated in spherical relativistic mean field theory with NLSH force parameter. We can conclude the following: (1) The pseudospin wavefunction splitting decreases from the proton drip line to the neutron drip line for all the pseudospin doublets. Only the neutron spin wavefunction splitting for the high energy level decreases monotonically with increasing the number of neutrons. (2) As for the certain isotope, when n=1, pseudospin wavefunction splitting increases monotonically with l increasing. When n=2, only the neutron spin wavefunction splitting increases monotonically with l increasing. When l=2 or 3, only the neutron spin wavefunction increases monotonically with n increasing. (3) The spin-orbital splitting for the neutron and proton is always closer to each other than their pseudospin pseudo-orbital splitting in the relativistic mean field theory.
A model of expanding pion sources in relativistic heavy ion collisions, when only hadronic matter is generated, is proposed. The two-pion correlation function at small relative momentum for such a model is obtained with two-pion interferometry at small relative momentum, and the relation between the real spatial parameter Re and the apparent spatial parameter Ra of the pion sources is given. The relation is different from the one when QGP is created. The difference can be used to test nonstatic, spherical quark-gluon plasma produced in relativistic heavy ion collisions. The relation also showes a scaling behavior.
A simple method for positioning cosmic rays is reported, using plastic scintillator bars with wavelength shifting fiber and photoelectron multiplier readout. The accuracy of positioning is 1cm. More than 4000 CsI(Tl) modules from BESⅢ calorimeter have been tested for light output and uniformity.
A GEANT4 based, Object-Oriented package, TrkExtAlg, is developed for extrapolating the BESⅢ MDC track into outer sub-detectors. The magnetic deflection and ionization loss of the particle in the BESⅢ detector is considered, the algorithm supplies the position and the momentum of the track in all the outer sub-detectors, as well as the error matrix at any given hit point with the multiple scattering effect taken into account. Through comparing the results of track extrapolation with the results of a full simulation and checking the results and application of track matching with hits in outer sub-detectors, TrkExtAlg is proved to be reliable.
BEPCⅡ, the upgrading project of the Beijing Electron-Positron Collider (BEPC), has been designed with a luminosity of 1033cm－2.s－1 at the τ-charm energy region. According to the beam-beam simulation results, the luminosity of BEPCⅡ~with a crossing collision angle of 11mrad is about 0.50×1033cm－2.s－1 with the original operation mode at the working point of 6.53/5.58. To increase the operating luminosity of the BEPCⅡ, a low momentum compaction factor (αP) collision mode has been studied which can increase the luminosity to 0.54×1033cm－2.s－1. If the bunch length of the low αP mode is reduced from 1.5cm to 1.2cm, a mode with vertical beta function at IP equal to 1.2cm could push the luminosity to 0.828×1033cm－2.s－1 at the working points 6.53/5.56.
We numerically studied the microbunch instability driven by Coherent synchrotron radiation (CSR) in a magnet bunch compressor. High-frequency density perturbation may be significantly amplified when an electron beam passes through the Beijing XFEL Test Facility (BTF) magnet bunch compressor Ⅱ. The dependence of CSR-driven microbunch instability on bunch twiss parameters is sensitive. Dangerous area of twiss parameters is outlined.
Leptospira interrogans peptide deformylase (LiPDF) is an important Zinc metalloprotein and plays a key role in protein synthesis of Leptospira interrogans, an ubiquitous environmental bacterium that can cause the infections of animals and humans. It is an attractive target for the design of new antibiotics since the deformyling apparently does not occur in the cytoplasm of eucaryotic cells. In this paper, we probed the protein in pH3.0 solution by X-ray absorption near-edge structure (XANES) spectroscopy. We quantitatively determined the local structure around the metal center using MXAN procedure, which is based on Multiple Scattering theory. The experimental XANES spectrum of LiPDF has been reconstructed perfectly using suitable initial structure mode, and the corresponding local structure of the active center provides structure information for understanding the pH-dependent enzymatic activity.
A interaction model of multi-photon process in the "multi-coupled-atom-cavity" system is constructed. In terms of the cavity quantum electrodynamics, the properties of quantum information transfer in the process of coupled atoms interacting with cavity fields are studied, and the effect of the coupling between atoms on the quantum information transfer is analyzed. It is found that quantum information can be transferred back and forth or be preserved between the cavity fields and atoms in certain time period. The dipole interaction between atoms leads to the quantum entanglement information partially transferred and partially preserved.
With the coupled Dyson-Schwinger equations in the framework of the unified QED3 theory, we study the phase transition between the antiferromagnet(AF) and the d-wave superconductor (dSC) of planar cuprates at T=0. By solving the coupled Dyson-Schwinger equations both analytically and numerically in rainbow approximation in Landau gauge and comparing the obtained results with that given in the 1/N expansion, we find that there exists a chiral symmetry breaking from dSC phase to AF phase when the quasi-fermion flavors N≤4 in half-filling and the AF phase can possibly coexist with the dSC phase in the underdoped region. By comparing the pressure between the coexistent AF-dSC phase and dSC phase, we find that AF-dSC coexisting phase is the stable phase, the AF phase can then coexist with the dSC phase.
The BWO(Backward-Wave Oscillator) slow-wave structure was optimized by the KARAT code, and the experiment was performed at the RADAD303 accelerator flat under the condition of the electron beam with the voltage of 177kV, the current of 785A, and magnetic field of 1.7T. TE11 mode millimeter wave was generated, whose peak powe is 18MW, frequency 39.8GHz and pulse duration 3ns.
Since its invention in 1990s, GEM has drawed great attention and wide studies in the field of particle physics and radiation imaging because of its high gain, high position resolution and high cout-rate capbility, many applications have been proposed, especially for the readout of TPC. Compared with traditional readout detector, mainly MWPC (Multi-wire proportional chamber), GEM has many advantages and also a lot of challenges. Many institutes are carrying comprehensive R&D of TPC based on GEM readout in order to evaluate whether it can meet the unprecedented requirement of future ILC. This paper reviews their recent result.
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