2003 Vol. 27, No. 2
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The detection efficiency corrections for the particle identification and kinematic fit selection criteria are investigated for the branching fraction measurements in ψ′decays into ωπ+π－, b1π,ωf2(1270), ωK+K－, ωp, φπ+π－, φf0(980),φK+K－, φp final states using 4×106ψ′data sample collected at BEPC/BES. Based on the corrected efficiencies, the preliminary results of these decay channels have been obtained, and the "12%" rule predicted by perturbative QCD theory has been tested.
The anomalous scaling property inside jets produced in e+e－ Collisions at s91.2GeV is studied using Monte Carlo method. A new variable r is applied, which has very good anomalous scaling property. The relation between the scaling indices of different orders is investigated. The Lévy index for the hadronic system inside jets is obtained, which turns out to be μ=2.498±0.025, very close to the same index of hadron-hadron collisions. On the contrary, the Lévy index of e+e－ collisions is 1.701±0.043, being less than 2. Since the multi-hadron production in e+e－ collisions is dominated by hard gluon emission or hard parton branching, while the parton fragmentation into jet, like the multi-production in hadron-hadron collisions, is a soft process, the above results suggest that the value of Lévy index may provide another signal for the qualitative difference between hard and soft processes.
In this paper, we recalculate pion virtual Compton scattering in perturbative QCD. Our calculation treats real Compton scattering as a limint case in which the mass of the virtual photon equals zero. To prove the validity of our method, we place our focus on comparing the effects of different distribution amplitudes on the prediction of physical observables.
The antibunching properties for the eigenstates of the Kth powers (K≥3) of the annihilation operator of the q-deformed non-harmonic oscillator are investigated. The numerical method is used to study the properties influenced by the parameter q. The results show that the eigenstates exhibit antibunching effects in a number of intervals of x│=β│2, which reflects the intensity of the non-harmonic oscillator in q-deformation generalized coherent state. The effects are evidently influenced by the parameter q. When q is taken values departure from 1 greatly, these intervals become larger, and shift toward the positive x direction.
With the extensive air shower (EAS) array at Mt. Liang Wang (735 g·cm2,245°N,102.9° E,Kunming China) it is able to measure the muon density spectrum at a fixed distance from the core of EAS in the knee region. The spectra at two different fixed core distances (25m≤core distance<30m,30m≤core distance<35m) were obtained from 4.4×104events collected in 1994 with criteria 5×104≤size≤1.6×107 and 10°≤θ<30° that show obvious kinks. Monte Carlo simulations for the EAS development and detection with same selection criteria in the array triggering and the analysis procedure have been performed in order to relate the local muon densities to primary energy. As a result,we have deduced that the average position of the knee (Eknee) is at about 1.7×1015eV and the average difference of the slopes of the primary energy spectrum before and after the knee (Δγ) is about 0.43. This work corroborates the first result (Eknee=5PeV,Δγ=0.3) reported by KASCADE. It authenticates reliably the existence of the knee at the primary energy spectrum by another composition of EAS - muon composition (more direct than electron composition). Based on the results obtained by two experiments,the difference of slopes of cosmic ray primary energy spectrum before and after the knee is close to 0.4 that is accepted widely,while the energy of the knee is different from the accepted 3PeV.
The Kaon condensation in neutron star matter is calculated in the framework of the density dependent relativistic mean-field theory. The present results show that the critical density for the Kaon condensation is ～2.75ρ0, while the critical densities for the URCA process in neutron star matter are ρρ0≈3.16 for the parameter set fitted to the DB nucleon self-energies of nuclear mater with the momentum-dependent correction, and ρρ0≈2.25 for the parameter set without the momentum-dependent correction. Then,influences of the two different model parameter sets on the equation of state of neutron star matter are discussed.
The fission fragments in the reaction of 40Ar+197Au have been measured coincidently with light charged particles at 35MeV/u by using large area position sensitive detectors and Si-detectors. The velocities of the fissioning compounds are deduced based on the fragments and the excitation energies of the compounds calculated with a hypothesis of massive transfer and taking into account the influence of pre-equilibrium emission of light particles. As the same time,the temperatures of the compounds are extracted by using the energy spectra of the backward light charged particles measured coincidently with fission fragments. The temperature-excitation energy curve does not present the behaviour predicted by the theories.
Six superdeformed bands of odd-odd nucleus 194Tl in A～190 mass region are studied using the particle-number conserving method for treating the cranked shell model with pairing interactions. Calculated results agree with experiments very well. Based on our calculation the configurations of the six superdeformed bands are assigned and the influence of blocking effects of proton and neutron on moments of inertia is investigated in detail. The variation of moments of inertia with rotational frequency is mainly attributed to the intruder shells (neutron N=7 and proton N=6), whereas the contributions to moment of inertia from other shells remain almost unchanged with rotational frequency.
From Friedlberg-T. D. Lee's non-topological soliton model, a new quark confining potential is obtained. Using this potential, the electromagnetic form factors of nucleon are predicted and are compared with experimental data. The theoretical results are in good agreement with data. Therefore, theory reproduces a good explanation of experimental measurements.
The isospin effects on the fragmentation process and the role of momentum dependent interaction in heavy ion collisions at intermediate energy are studied systematically by using isospin dependent Quantum Molecular Dynamical model (IQMD). The results show that multiplicity of intermediate mass fragments
The experimental data of the 13C(d,p) 14C reaction are used to extract the asymptotic normalization coefficients of the overlap integral, the root-mean-square radii
It is pointed out that contribution of the πNN processes to the structure functions of the nucleon should be calculated by taking the recoil nucleon as a physical nucleon. The obtained result for the contribution to Gottfried sum rule violation is smaller than the corresponding result obtained earlier in literature, where Gottfried sum rule was assumed to be valid for the recoil nucleon. It leaves more space to other mechanisms leading to such violation. Some other consequences are also discussed in this paper.
Using modified surface delta interaction,enlarging the gds configuration space to include the 1h11/2 states with the negative-parity,the deformed Hartree-Fock calculations for the seven nuclei (104Cd,106Cd,108Cd,110Cd,112Cd,114Cd and 116Cd) are performed. The ground-state and some particle-hole excited configurations are obtained. The calculated results show that there exist form transition and shape coexistence from mass number 104 to 116,and that the single-particle energy spectra are different not only for different mass number but also for different configurations of nuclei. At the same time,the approximate angular momentum projected Hartree-Fock(PDHF) method is applied to nuclei 108Cd and 110Cd. And both of their positive- and negative-parity bands are obtained. The results of calculated energy spectra are consistent with experimental spectra well.
Using a hadron and string cascade model,LUCIAE,the Φ meson production in relativistic nucleus-nucleus collisions was systematically investigated from AGS energy,to SPS,to RHIC,up to LHC energy. After considering the energy dependence of the model parameter in string fragmentation function and fitting it to the experimental data of charged multiplicity,the results of Φ meson yield were comparable with experimental data. The obtained string fragmentation variable showed a saturation in dependence with energy,that might be a qualitative representation of the energy dependence of nuclear transparency.
The significance of monitoring of space radiation environment and the application of telescope consisted of Semiconductor charged particle detectors in space physical science are described. The partial results of the measurement of space radiation environment,solar proton event and geomagnetic storm by the home made telescope system in satellite are presented.
More than twenty MRPC modules made of Chinese material in our Lab are tested by using cosmic rays. The test bench of cosmic rays is described in detail. The time resolution of the cosmic rays telescope is around 70ps. The time resolution of MRPC in cosmic rays testing is around 90ps. The MRPC detection efficiency,the ADC spectrum and the induced signal influence between cells are presented too.
The development of beam diagnosis at RIBLL has been carried out. There are three kinds of diagnosis devices, i.e. the transmittal Faraday cup, plastic scintillator and two dimensional position sensitive PPAC. The Faraday cup is usually used to measure primary beam in the experiments. The scintillator readout with photomultipliers is set to monitor the primary beam in low intensity during tuning RIBLL. The PPACs (C1,T1,C2,T2) with 100mm×100mm of sensitive area are installed to measure the RIB profiles. So the performances of RIBLL are improved.
A new way in electron beam emittance measurement with Cerenkov radiation "double imaging" method is proposed in this paper. In the standard emittance measurements with optical diagnostics such as Cerenkov radiation, OTR (Optical Transition Radiation), fluorescence screen or BMP (beam profile monitor) etc., the emittance is indirectly calculated through quadrupole-scanning technique, with the prior ssumption that the beam phase space density distribution is ellipse, which will certainly induce systematic error when the beam profile is quite irregular or the space-charge effects can not be omitted. In proposed method, the Cerenkov radiation pass through a 1-meter focal-length thin convex lens, and a CCD camera is used to capture two images of Cerenkov radiation at the focal plane and at the image plane of the lens respectively. Then, with image processing technique, we acquire the angular divergence information of the electron beam from the image of the focal plane and the radial distribution information from the image of the image plane, which we call Cerenkov radiation "double imaging" method. Therefore, the emittance can be directly attained according to the definition of the RMS emittance. By this method, we can measure the actual phase space distributions without making any prior assumptions about the density distributions. Compared with other general measurements, this "double imaging" method has advantages of simpler equipment, higher precision and wider application. This paper also presents the computer simulation results of emittance measurement on the DC-SC (DC-Superconducting) photocathode injector of PKU-SCAF (Peking University Superconducting Accelerator Facility) being built at Peking University.
The new DCCT measurement system is developed for Hefei Light Source (HLS). The system is composed a PCT system, a DCCT shielding system and a DCCT data acquisition system. The magnetic shielding against stray fields suppressed zero drifts of DCCT from 1mA to 10μA. In new DCCT measurement system, the resolution is about 1μA rms, the accuracy is about 0.1%.
To meet the upgrading goals of the BEPCⅡ-linac, the beam modeling and studies on optimizing the optics for high current electron and positron beams are carried out. An optics-tuning scheme is defined. The effects of initial beam axis deviation and machine alignment errors on normalized beam emittance growth and on beam orbit offset are systematically studied, and the orbit correction with "1-to-1" correction scheme is modeled.
Electronic structure of Co films grown by molecular-beam epitaxy on Cu (111) surface was studied by Synchrotron Radiation angle-resolved Photoemission Spectroscopy. The peak intensity of the surface state at the Γ point of Cu(111) surface Brillouin zone still can be distinguished even at the coverage of 2ML, which means that the growth mode is not the two-dimensional layer-by-layer mode. With changing the momentum along the direction of Γ-Λ-L of Brillouin zone of bulk copper by varying photon energy, we find that the most prominent peak of cobalt film both at the coverage of 1ML and 2ML disperses like that of the surface of Co(0001). With a fixed photon energy for the coverage of cobalt from 1ML to 2ML, the changes of cobalt energy band were obtained. It shows that the 3d-band modification do exist because of the interaction of substrate and film atoms at the initial stage of growth. Compared with theoretical calculations, we find that films show ferromagnetic characters even at 1ML thickness, and they might grow as bilayer island at the initial period of growth.
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