2000 Vol. 24, No. 11
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The alignment of energetically distinguished cores in a part of family events observed with Kanbala K0-K7 emulsion chambers is analyzed, and compared with the simulation results given by COSMOS and CORSIKA code. It is shown that the fraction of events with alignment in the experimental families increases with the visible energy of families but this effect can not be explained by the conventional simulations. The Criteria of identifying γ-rays and hadrons in the family events are also discussed.
We studied an SU(3)L×U(1)X electroweak model. By requiring M2z1-M2w/ cos2θw to be less than experimental value we abtain a lower bound on MZ′ The relation between MZ′ and MU (MV) then gives a lower bound on MU (MV). We further consider the KL－KS mass difference due to Z′ exchange and obtain stronger lower bounds on MZ′ and MU (MV).
The longitudinal structure function FL and the ratio RL of the longitudinally to the transversely polarized virtual photon absorption cross section are mainly dependent on the gluon distribution in the small-x region. And the initial gluon distribution at Q2= Q20 determines whether we must consider the shadowing corrections to the evolution process. In this paper we use the new evolution equation to analysis FL and RL, and found there must be Shadowing effects in the parton evolution process.
We calculated the Pseudo-Goldstone bosons (technipions, top-pious) corrections to the cross-section a of the process e+e－→bs in topcolor-assisted multiscale technicolor model at LEP Ⅱ energy region. Our results show that, with reasonable value of the parameters, the cross-section is one order larger than that predicted by the standard model. We discussed the possibility of detecting this rare event at the B-factoly.
A relativistic quark potential model is employed to study the electromagnetic form factors of the proton and neutron. Moreover, the pion meson cloud effect is also taken into account. The nucleon wave function is described in an extended Fock space with the intermediate states N and △. The result shows the important role of the meson cloud on the neutron electroic form factor.
NA22 experimental data of the triplet seagull effects show that the Doppler effects of the hadron emission sources exist exactly in the hadron-hadron collisions. Every source possesses the same average energy (CMS) approximately. The collective seagulleffects can be also explained by the (aQ)vKv (aQ) distributions (Generalized functions). The dynamical structure of a hadron emission source is discribed by the (aQ)vKv (aQ) distributions. The anomalous dimensions of the picnic quantum fields are rB(gR) =－0.045±0.012, which control the singularities of the production amplitude in quantum field theory. The mathematical parameter= 4－D (the dimension D of space time) in the Feynman integrals can be replaced by the anomalous rB (gR) of the quantum fields for the regularization. (－2rB (gR)ε/2=1/1n(A2/m2)A→∞).
Through study of the prompt r-rays emitted in the spontaneous fission of 252Cf, high spin states of neutron-rich odd-A 145,147Ce nuclei have been investigated. The levels in 147Ce have been extended. A collective band in 145Ce have been identified for the first time. The results from the particle rotor model calculations indicate that the yrast bands in 145Ce and 147Ce originate from vi13/2 orbital coupling and the ground states of 145Ce and 147Ce originate from (vh9/2,vf7/2) and vh9/2 configiration, respectively. No obvious octupole deformation was observed in these two isotopes, but a side band obtained in 147Ce may show some octupole correlations.
JON MyonGil, JIANG Zhuo, ZHANG Zheng, J.H.Hamilton1, A.V.Ramayya1, B.R.S.Babu1,
J.K.Hwang1, W.C.Ma2, J.Komicki1, J.D.Cole3, R.Aryaeinejad3, M.W., Collective Band Structures in Neutron-Rich Odd-A 145,147Ce Nuclei[J]. Chinese Physics C, 2000, 24(11): 1018-1023.
From the simulation of intermediate energy heavy ion collisions by using the isospin dependent quantum molecular dynamics (IQMD), we have investigated the isospin effects on the multifragmentation process in intermediate energy heavy ion collisions: reverse reactions 120Xe + 40Ca, 120Cd+ 40Ar, 76Kr + 40Ca and 76Zn + 40Ar. To describe isospin effects appropriately, QMD was modified properly. The density dependent mean field contains correct isospin term including symmetry energy and Coulomb potential. The in-medium n-n cross section is different for neuron-neutron (proton-proton) and neutron-proton collisions. And finally Pauli blocking was counted by distinguishing neutrons and protons. In addition, the initial condition of the ground state of two colliding nuclei also contains isospin information. The calculated results show a prominent isospin effects for the multifragmentation process among the colliding systems with different neutron or proton excess. The correlation between Nimf and Nc for neutron-deficient systems are always larger than those for neutron-rich systems in intermediate energy region for all of colliding systems studied here, and the mechanism causing the above isospin effects is mainly due to the fact that the mean n-n cross section for the neutron-rich system is smaller than that of neutron-deficient system. Thus one can combine experimental studies and theoretical simulations to investigate the isospin effect of multi fragmentation Process and to extract the information on isospin dependence of in-medium n-n cross section from the correlation between Nimf and Nc.
With the use of modified derivative scalar coupling (MDSC) model, the nuclear surface properties and the spin-orbit potential in semi-infinite nuclear matter have been investigated in the framework of relativistic Thomas-Fermi and Hartree approaches. Our results shoW that the spin-orbit potential has ben improved by the tensor coupling. However, the surface tension and the surface thickness are still too small. The effects of a-melon mass on the surface properties and the spin-orbit potential have also been discussed.
The offset of the beam position monitor (BPM) with respect to the magnetic center of the quadrupole can be determined by the method of the beam-based alignment. The BPM alignment accuracy can be improved by one order of magnitude compared with conventional surveying techniques. This paper gives a brief intreduction to the principle of the beam-based alignment and the description of the preliminary experiment performed on the BEPC storage ring. The considerations of the further experiments are also given.
A new method that uses transmission grating (TG) for diagnosing the output character of synchrotron radiation beamline was introduced. Using TG the energy calibration was processed and the energy resolution was measured in 3W1B beamline of BSRF. The behavior of high order component of the beamline was qualitatively given.
The effect of the crystal's type and treatment on the performance of gamma camera consisting of planar crystal and position sensitive photomulitiplier tube (PSPMT) is studied via experiment. The results demonstrate that: (1) treatment of the edge surface of the crystal is very sensitive to the shrinkage of image, and the side-absorptionsurface is the best choice; (2) the intrinsic spatial resolution of the CsI (T1) crystal camera is worse due to its low light yield: in the center part it is - 1cm (FWHM) for 2mm aperture collirnated 241Am source; while using NaI(T1) crystal, it is -4mm.
Fine structures appearing in boron nitride(BN) sample bomparded by N2+ ion (60keV) were examined by JEM-200cx high-resolution transmission electron microscopy (HRTEM) at 200kV accelerating voltage. In the curved region of plate-like h-BN crystal sp2 sheets (spacing 0.33nm), it was observed that the t-BN structure with an average interplaner spacing of 0.35 nm was formed. Although the mechanism of formation of the t-BN structure is nuclear, it appears that our discussion based on the viewpoint of beam-solid interaction may be critical in understanding the growth process of the t-BN structures.
Two independent measurements of excitation functions for the 19F+93Nb dissipative heavy ion collisions have been performed at incident energies from 100 to 108 MeV in steps of 250 keV. The two measurements differed by two target foils, 70 and 71μg/cm2, respectively. All the other experimental conditions were kept to be identical in hath experiments. The data indicate nonreptaludbility of the non-self-averaging oscillating yields in the two measurements. This supports recent theoretical predictions of extreme sensitivity and chaos in complex quantum collisions.
The positive parity collective states in the even-even 128—150Ce isotopes are studial in the framework of the interacting boson model. A schematic Hamiltonian able to describe their spectra and transition is used. It is found that both the light and heavy even Ce isotopes are in the transition from the vibrational limit to the rotational limit. From 146Ce onward, the isotopes are nearly perfect rotors.
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