2001 Vol. 25, No. 2
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A method is introduced for the measurement of integrated luminosity in R scan by large-angle Bhabha events. Compared with the previous method, some improvements have been made in both events selection and determination of detection efficiency. Several methods are employed to check our results and have given compatible luminosities within errors.
Based on Variational-cumulant expansion (VCE), through calculating Polyakov line in the SU(2) gauge model at finite temperature and considering the similarity of finite size interaction in VCE method with the finite volume effect in Monte Carlo (MC) simulation, a new approach is adopted to determine the critical couplings for the deconfinement phase transition. New results of VCE which are close to MC data manifest that new approach is much more effective than the traditional one and show that VCE analysis is consistent with MC simulation.
We discuss the contributions of PGBs (technipions and top-pious) to the top quark production in TC2 theory at the high energy e+e－ linear collider (LC) experiments. We find that the corrections to the production cross section σtt mathly come from top-pious. The corrections of the charged top-pious are significantly large in most of the parameter space. With reasonable value of the parameters, the correction to σtt can reach about 8% which may be detected at LC experiments.
Isotopes,130Nd and 140Tb were produced using enriched targets 96Ru and 106Cd, respectively,bombarded by 36Ar ion beam. The two nuclides were identified and studied by a He-jet tape transport system in combination with "X-γ" and "γ-γ" coincidence measure- ments. The half-life of 130Nd was determined to be (13±2)s. The EC/β+ decay scheme of 130Nd was proposed for the first time, and the spins and parties of the ground-state and observed low-lying states in the daughter nucleus 130Pr were speculated tentatively. The previous simple EC/β+ decay scheme of 140Tb was revised, and the spin-parity of its groundstate was assigned to be 7+.
The correlations between the emitted fragments at θlab=15°and the light charged particles(LCPs) at the close geometry configuration in the reaction of 25MeV/u 40Ar+115In were measured. The energy correlations between fragments (4≤Zf≤14) and the LCPs including proton, deuterium, tritium and a particle as well as the energy spectra of the LCPs were obtained. The result shows the existence of sequential decay mechanism. It is found that the peak position of angular correlation is at the small angles and the most probable correlation angle is at 2°or so; The peak positions of the two components in the energy spectra of LCPs increase gradually with the mass of correlated partner; The lighter primaly products are more easier to be excited and decay to IMFs and the LCPs. In the Sequential decay, the yield of the LCPs with more heavier mass is higher than that of the lighter LCPs. The result reveals that the total correlation yield ratios summed over the fragments of Zf=4—14 are 1: 1. 3: 1. 78: 7. 57 for proton, deuterium, tritium and a particles, respectively.
A comprehensive investigation of the superdeformed bands observed in 142,143,144,147Eu was given. The fluctuation in the transition energies has been removed. The smoothed transition energies were fitted by the ab-expression or its modification. The spins of these bands, except for band 4 of 147Eu, have been assigned conclusively. The exit spin in 143Eu was proud to be 29/2, different from that asserted to be determined experi- mentally but remains to be confirmed. The corresponding values in 142Eu and 144Eu(a) are 21 and 28, lower than those proposed in the literature by 6 and 8 units, respectively. Two pairs of superdeformed bands in 147 Eu, i. e. bands 1,5 and bands 2,3 were proposed to be signature partners. The exit spins are 53/2 and 63/2 for the former pair, and 43/2 and 41/2 for the latter pair. In addition, both of them have a rather large de-coupling constant(≈-1), implying they are of K=1/2 and built on the single particle level ν↓ or π ↑. This assignment may be helpful for the studies of the so-called identical bands and pseudospin problem. The signature partner pairs observed in 144,148Eu are not included in the investigation.
The variations in moments of inertia (J(2) and J(1)) with rotational frequency for the series of yrast SD bands in even-even nuclei, 192—198Pb(1) and 198Po(1), are investigated by using the particle-number conserving method for treating the pairing interaction (monopole and quadrupole). The observed co variations of J(2) and J(1) are reproduced quite well in the PNC calculation, particularly the microscopic mechanism (the contributions from each major shell and each cranked Nilsson orbital) is clearly displayed. It is found that the smooth rise of J(2) with ω is attributed to the contribution from the intruder shells (neutron N=7 and proton N=6).
Exact algebraic solutions of a hard-core Bose-Hubbard model for the description of nearest orbit pairing interaction in well-deformed even-even nuclei were derived based on a simple algebraic routine. Excitation energies and the corresponding wavefunctions of the model were obtained. Further extensions to arbitrary spin cases and the corresponding Fermi-Hubbard model were also presented.
Nuclear transition charge/current density operators are composed according to valence nu-cleon degrees of freedom. By using boson expansion technique, a microscopic theoretical method (BE method) about the transformation of the fermion density operators into boson density operators is established. Thus, calculations of the nuclear charge/current densities can be carried out in the boson state space by taking advantage of the eigenfunctions of the microscopic IBM. Associated with the formal theories of electron-nucleus scattering and nuclear electromagnetic transition, a microscopic approach, which can be used to study nuclear transition charge/current densities, various form factors, differential cross sections, reduced transition rates, electromagnetic multipole moments, g factors and so on, is built up. The preliminary results based on the microscopic sdIBM-2 has indicated that the physical quantities mentioned before can ha described well in the framework of the microscopic approach. The preliminary calculations of spectrum, E2 transition boson structure functions (BSF) and transition charge density from 21+ to 01+ in 192Os are carried out in terms of the present approach in the frame of the microscopic ed IBM-2. It is found that a reasonable description of these physical quantities has been achieued.
A general expression for nπ correlation function is given when there are multi-pion correlations in the choices of correlated nπ and uncorrelated nπ. Using this expression, the two-pion interferometry at small relative momentum which takes account for multi-pion correlations is studied, the relations between the pion source parameters from the two-pion interferometry and the three- pion interferometry are obtained analytically, and comparison is made with the experimental results of central relativistic heavy ion collisions 1.8 A GeV Ar+Pb.
Data offline calibration and reconstruction for the BES-Ⅱ TOF system are reported in this paper. After applying calibration constants to correct the measured raw data, a the resolution of 180 ps is obtained for the new TOF system. The power of charged particle identification is improved. The momentum for the 3σπ/K separation goes up to 0.93 GeV/c.
A metallic cage made by sputtering silver film onto a thin nylon thread through a specially designed fixture is used as perturbing object to measure the higher modes in a Xband accelerating structure. The fabrication and calibration of the Cage are described in this paper. It is found that this type of perturbation object has the advantages of high sensitivity and high resolution. Using the cage as bead, the longitudinal electric fields of TM110 mode in a X-band 30cm structure are obtained with bead pull measurements.
Based on the general theory and related technique of 1/3 integer resonant extraction, main principle of layout for momentum-amplitude selection method is studied in detail and some simple analytic formulae are given. The design of slow extraction system for Beijing Proton Therapy Synchrotron (BPTS) is then given as an example by considering its lattice. The results are also compared with simulated calculation. Study shows that an extraction beam for BPTS with extraction efficiency above 98% and momentum spread of 0.11 % can be obtained.
The formation of bended BN nanostructures and small BN cage-like molecules, under Nc2+ ion-bombardment of BN samples, is reported. The analysis of high-resolution transmission electron microscopy indicates that bending the flat sp2 layers with strain or lattices defects directly under the mechanical deformation forms these BN nanostructures. In addition, the cages in diamlter range from about 0.4 to 1.8nm, closing to those of the B12 N12, B16N16, and B208N208 octahedral, were observed. The origins of the bended BN sheets and small BN cages were discussed based on the viewpoint of beam-solid interaction.
The production of dileptons in the intermediate mass region in QGP has been studied on the basis of a relativistic hydrodynamic model. Due to the influence of the phase boundary on the evolution of the QGP system and the high initial temperature of the QGP produced at RHIC energies, the quark phase contribution is much more important than that from hadronic interactions and even comparable with that from background sources. It is shown that such an enhancement is a signature for the QGP formation.
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