2006 Vol. 30, No. 10
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In the angular distribution measurement of ψ′→pp, the sample of J/ψ→pp selected from 58M J/ψ events with high statistics is used to determine the polar angle dependent efficiency, and to correct the Monte Carlo efficiency in ψ′→pp. The systematic error of this method is also analyzed. The obtained efficiencies and related errors are used for the measurement of angular distribution of ψ′→pp.
The resonance DsJ(2632) observed by SELEX, has attracted great interests and meanwhile brought up serious dispute. Its spin-parity, so far has not finally determined and if it exists, its quark-structure might be exotic. Following the previous literature where DsJ(2632) is assumed to be a radial-excited state of 1－, we consider the possibilities that it might be a qq ground state of 2+ or the first radial-excited state of 0+ DsJ(2317) and re-calculate its strong decay widths in terms of the Bethe-Salpeter equation. Our results indicate that there still is a sharp discrepancy between the theoretical evaluation and data.
Classical and quantum oscillator of generalized anharmonicity is solved analytically up to the linear power of ε by using the multiple-scale perturbation method. The commutation relation of position and momentum operator can be simplified easily and the quantum solutions transformed into the classical form conveniently under the extreme conditions, which are different from the earlier multiple-scale perturbation theory. Moreover compared with the Taylor series solution, the frequency shifts in our solutions appear in the expression of oscillations of all orders in both classical and quantum cases, so multiple-scale perturbation method is more suitable for solving the weak-coupling anharmonic oscillation than the Taylor series approach.
We propose an effective Lorentz-violating electrodynamics model via static de Sitter metric which is deviated from Minkowski metric by a minuscule amount depending on the cosmological constant. We obtain electromagnetic field equations via the vierbein decomposition of tensors. In addition, as an application of the electromagnetic field equations obtained, we get the solutions of electrostatic field and magnetostatic field due to a point charge and a circular current loop respectively. We also make some discussion on the implication of the Lorentz violation effect in our electromagnetic theory.
Within the Brueckner-Hartree-Fock framework, the equation of state and the properties of newborn neutron stars are investigated by adopting a realistic nucleon-nucleon interaction AV18 supplemented with a microscopic three-body force or a phenomenological three-body force. The maximum mass of newborn neutron star and the proton fraction in the newborn beta-stable neutron-star matter are calculated. The neutrino-trapping and the three-body force effects are discussed, and the interplay between the effects of the trapped neutrino and the three-body force are especially explored. It is shown that neutrino trapping considerably affects the proton abundance and the equation of state of the newborn neutron star in both cases with and without the three-body forces. The effect of neutrino trapping remarkably enhances the proton abundance, and the contribution of the three-body force makes the equation of state of the newborn neutron star much stiffer at high densities and consequently increases the proton abundance strongly. The trapped neutrinos significantly reduce the influence of the three-body force on the proton abundance in newborn neutron stars.
In terms of the relativistic mean field theory, which describes the hadronic matter, and the NJL model, which characterizes the quark matter, the influence of hyperon coupling constant on the properties of hybrid stars is studied. The numerical results show that with the increase of the hyperon coupling constant the phase transition density decreases, the equation of state in the mixed phase range stiffens, and the maximum mass and the corresponding radius increase. When the hyperon coupling constant increases from 0.73 to 1, the maximum mass of the star increases from 1.68⊙ to 1.82M⊙ and the corresponding radius of the star changes from 11.4km to 12.5km. The result also shows that the different hadronic equations of state have different influence on the properties hybrid stars. This model is suitable for describing the hybrid stars with big masses and small quark cores.
The high spin states of 106Ag have been populated via the 100Mo(11B,5n)106Ag reaction with a beam energy of 60MeV at HI-13 Tandem accelerator of China Institute of Atomic Energy. The gamma-gamma coincidences were measured using a gamma-ray detector array. By analyzing the gamma-gamma coincidence and their DCO ratios, the level scheme of 106Ag has been updated, in which twenty-six new gamma transitions and ten new levels are added. The rotational structure of 106Ag has been compared with its neighboring odd-odd isotopes and its configurations are discussed briefly.
In this paper, an improved nuclear density model is presented. The formulas of nuclear effect parameters RVA (x,Q2) and RSA (x,Q2) for the valence quark distribution and sea quark distribution in nucleus are derived, in which the connection between the nuclear density and the mean binding energy in nucleus is used. In terms of this model, the experimental data of the averaged nucleon structure function ratio of DIS process in l-A are well explained.
Within the framework of Dirac Brueckner-Hartree-Fock (DBHF) approach, we calculate the energy per nucleon, the pressure, the nucleon self-energy and the single-nucleon energy in the nuclear matter by adopting two different covariant representations for T-matrix. We mainly investigate the influence of different covariant representations on the satisfiable extent of the Hugenholtz-Van Hove (HVH) theorem in the nuclear medium in the framework of DBHF. By adopting the two different covariant representations of T-matrix, the predicted nucleon self-energy shows a quite different momentum and density dependence. Different covariant representations affect remarkably the satisfiable extent of the HVH theorem. By adopting the complete pseudo-vector representation of the T-matrix, HVH theorem is largely violated, which is in agreement with the result in the non-relativistic Brueckner-Hartree-Fock approach and reflects the importance of ground state correlations for single nucleon properties in nuclear medium, whereas by using the pseudo-scalar representation, the ground state correlation cannot be shown. It indicates that the complete pseudo-vector presentation is more feasible than the pseudo-scalar one.
The binding energies and root-mean-square radii of 26—32S and 22—28Si are calculated by the relativistic mean-field model with two sets of parameters TM2 and NL-SH. The calculated results are in agreement with the experimental data. The calculated form factors and differential cross sections of electron scattering on 32S and 28Si by the Eikonal approximation agree with the experimental data. Further calculations on electron scattering of S and Si isotopes are carried out, and the sensitivity of form factors on charge density is discussed. The form factor of electron scattering on unstable nuclei can be accurately measured in the future electron-nucleus collider. The theoretical predictions would be valuable for future experiments.
High-spin states in 158Tm were populated via the 144Nd(19F, 5n) fusion-evaporation reaction at beam energies of 108 and 112MeV. The previously known level structures have been extended and a new band structure has been identified. In addition, a previously identified four-quasiparticle band has been firmly connected to lower known states. This four-quasiparticle band is assigned to the πh11/2\otimes νh9/2(α=－1/2)\otimes (νi13/2)2 configuration and thus form a pair of signature partners with another four-quasiparticle band known as being built on the πh11/2\otimes νh9/2(α=+1/2)\otimes (νi13/2)2 configuration. The band based on the πh11/2\otimes νi13/2 configuration is observed to show anomalous signature splitting persistently, across the spin where a restoration to normal signature splitting is expected from systematics. Signature inversion is also established in the doublet πh11/2\otimes νh9/2\otimes (νi13/2)2 bands. Positive triaxial deformation is supposed to play an important role in the occurrence of the unusual signature inversions in the weakly-deformed doubly-odd nucleus 158Tm.
A new program of 3D-reconstruction of AMS02 Electromagnetic Calorimeter(ECAL) is developed. In the program, the direction reconstruction is iterated, and the corrections for fiber attenuation, transverse leakage and longitudinal leakage are performed. The program is tested by comparing the beam test data and Monte-Carlo simulation, and a good agreement is obtained.
In order to find rational explanation to the experimental result and possible methods to improve the performance of End-cap Time-of-Flight detector (ETOF) in BESⅢ, the Monte Carlo simulation of the detector is carried out by using Geant4 software package. The simulation data of PMT signal and the time resolution of the ETOF are given. The simulation and data analysis are mainly focused on studying the effect of the light transmission characteristic in scintillator when particle hits different position and different thresholds of PMT signal are chosen. The study can make reference for the improvement of ETOF detector in BESⅢ.
Intensive study has been done on low and medium energy section of proton and heavy ion accelerators. Many experiments show that spoke cavity is a very good candidate to connect low beta RFQ (radio frequency quadrapole) structure and high beta elliptical accelerating structure. A β=0.45, f=350MHz spoke cavity has been designed and a copper model spoke cavity has been fabricated at Peking University. In this paper, we put the emphasis on the analysis of HOMs (high order modes) of the spoke cavity.
A slow positron beam's stretching device has been designed and constructed on Beijing Slow Positron Beam, which based on a 1.3GeV linac. Positron was storage and stretching use Penning-Trap technique. Measurements show that the positron storage time strongly depends on the vacuum level in Penning Trap tube. Two modes was used to release the positrons from storage part, lowering VC while VB kept constant and rising VB while VC kept constant. This technique makes the pulsed positron beam to a quasi-continuous beam. The energy spread of positrons depend on in release mode. In the latter mode, we observe that the energy spread was reduced to a value less than 1.0eV. The time profile in user-defined waveform is more uniform. It is beneficial to reduce the probability of amplifier pileup especially in the case of measurement with high counting rate.
The input coupler for the accelerator cavity is one of the most critical parts in the RF accelerating system, its performance directly influences the RF power coupling to cavity, therefore, directly influences the cavity's quality. In the RF system of the BEPCⅡ, an antenna coaxial input coupler based on the design of KEKB superconducting (SC) cavity's coupler will be used. It's first to use this kind of high power coupler under the frequency of 500MHz in China. Some studies on this RF coupler have been done, which includes the multi-pacting (MP) effect, the transmission performance and the thermal layout simulation. The results show that (1) there are several serious MP points exist in this kind of coupler and some necessary ways must be taken to protect the coupler from destroying; (2) the transmission performance under BEPCⅡ operation frequency can be improved by optimizing the configuration of the coupler; (3) the heat-distributing pattern of the coupler from the simulation provides the important information for the cooling system design.
This paper introduces the turn-by-turn beam position measurements on BEPC storage ring, with the bunch-by-bunch system developed by HLS. The oscillation of the beam transverse position in each turn, the motion in phase space and the transverse damping time can be acquired. With the NAFF method, we could precisely analyze the beam frequency, and furthermore, could research on the beam tune shift. In particular, the resonance phenomenon induced by chromaticity sextupoles, which occurs under special work points, is observed and analyzed.
Magnetic circular dichroism spectroscopy using hard X-rays was established at 1W1B beamline and XAFS experimental station of Beijing Synchrotron Radiation Facility. The left and right circularly polarized X-rays were obtained by converting the incident linearly polarized X-rays using a phase retarder made of diamond crystal working at Laue geometry．XMCD spectra of disordered Pt-Fe alloys at Pt L2 and L3 edge were measured in transmission mode and a dramatic XMCD signal was observed. The performance of this method was evaluated and demonstrated.
The photon transportation in radiotherapy is studied based on Monte Carlo method. The dose calculation based on the MC simulation package DPM has been carried out, and the results have been visualized using MEX technology of Matlab. The dose results of X-ray in homogeneity and inhomogeneity medium have been compared with experimental data and those of other MC simulation package, and these results all agree. The calculation method we proposed has the advantage of high speed and good accuracy, therefore, is applicable in practice.
The X-rays generated and transported in target bombarded by electron beams in CT have been simulated with Monte Carlo code MCNP4. Photon efficiencies and forward directional characteristics of X-rays for several kinds of often-used targets were calculated and analyzed. Calculations show that as the thickness of the target increases, the photon efficiency increases and reaches a maximum, and then drops sharply for gold and tungsten target, while drops gently for cooper target. Also, the photon efficiency for cooper target is relatively small, but the angular distribution shows good forward directional characteristics, with the dose rate in the forward direction equivalent to those of tungsten or gold target. Experiment results show that the dose rate in the forward direction of a copper target is higher than that of a tungsten target for 20MeV electrons, while the angular distribution presents better forward directional characteristics compared with a tungsten target.
The Beijing intense slow positron beam facility has restricted running time of the BEPC-LINAC designed for BES and BSRF operation, We have therefore designed and constructed the plugged-in 22Na based slow positron beam section in the Beijing intense slow positron beam line with which we can supply continuous slow positron beam for debugging of newly-built positron annihilation measurement systems and saving running time of the Beijing intense slow positron beam. The plugged-in 22Na based slow positron beam section includes positron source(22Na), positron moderator, E×B slow positron energy filter, multilevel electrostatic acceleration tube, radioprotection, magnetic transport system and vacuum system, etc. The new slow positron beam line will be running on April, 2006.
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