2002 Vol. 26, No. 1
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Di-gluon fusion mechanism might account for the large branching ratios of B→Kη′. But because we know little about the effective η′ɡɡ vertex, there are large uncertainties in perturbative QCD estimations. In this paper, we try several kinds of η′ɡɡ form factors and compare the numerical results with the experiment. We find that, though we know little about η′ɡɡ form factor, if di-gluon fusion mechanism is important in B→Kη′, the branching ratios of the decays B→K*η′ would be around 10－5 which can be tested by future experiments.
The decay mode of J/ψ→π03(π+π－) was studied very little before. There are no informations except branching ratios for this channel in PDG book which based on less than 0.2×106J/ψ events of MARKⅠ. Now, BESⅠ has a data sample of 7.8×106J/ψ events, we can make more accurate results than MARKⅠ. Total of 3290±43 J/ψ→π03(π+π－) events including 1275±86 J/ψ→ω2(π+π－) events are selected. J/ψ→π03(π+π－) and J/ψ→ω2(π+π－) events have been generated with MC simulition for calculating events selection efficiency. BESⅠ result is: Br(J/ψ→π03(π+π－))=(2.52±0.06±0.43)% and Br(J/ψ→π03(π+π－))=(1.31±0.09±0.21)%. Meanwhile, we studied the invariant mass of 4π and ωππ to find interesting signals. It seems that there is a peak at about 1.74GeV in the invarianat mass spectrum of 4π, and a enhancement was also found at about 1.9GeV in the invariant mass spectrum of ωππ. It is not clear whether they are from resonances or background. Therefore, more work in detail is still going on.
Under conditions near the center of the Sun, it shows that 7Be atoms are completely ionized between R=0 to R=0.1217R⊙. The newly calculated 7Be and 8B solar neutrino fluxes are about 4.00×109cm－2·s－1 and 6.18×106cm－2·s－1, while the corresponding predicted values of the standard solar model are 4.80×109cm－2·s－1 and 5.15×106cm－2·s－1,respectively. It will further increase the discrepancy between the observed and the predicted neutrino fluxes in Super Kamiokande neutrino experiment.
In the constituent quark model, light baryons are considered as the systems of the constituent quarks with confining interaction and with a chiral interaction mediated by Goldstone bosons. Here the masses of the N and Δ and their splitting are investigated based on a relativistic quark model approach with inclusion of pion meson cloud. Pseudoscalar π-quark interaction is employed to study the coupling between the mucleon and the π. The results show the contributions of the one-gluon-exchange potential and of the pion meson cloud to the N-Δ mass splitting. Moreover, our numerical analyses indicate a difference between the relativistic and the nonrelativistic treatments.
We introduce the lagrange multiplier method to study the stability of a classical solution. We analyze the Hessian form of a starting point in the O(3) sigma model and generalize the result to the gauge theory. We conclude that the stability of a classicalsolution of the gauge theory is determined by the second variation of the effective Lagrangian including the contribution of the lagrange multiplier. The variational sign of the classical energy functional is a judgement of the solution stability.
The reaction cross sections σ R of F isotopes on carbon target were measured at intermediate energies via the transmission method. It was found that the reaction cross section of 17F has a little enhancement compared with that of its neighbor isotopes. The difference factor d has been deduced from the measured σ R by using the BUU model and Glauber model. It is enhanced also for 17F compared with its neighbor isotopes. From the above analysis, a possible proton skin structure is suggested for 17F.
Production of helium projectile fragments in 16O-emulsion interactions at 60 A GeV is investigated. The total charge changing and partial production cross-sections are measured experimentally on the basis of helium multiplicity. The multiplicity distribution of helium projectile fragments obeys a KNO scaling. In the peripheral collision of 16O at 60 A GeV in nuclear emulsion, the production of target fragments depends on the multiplicity of helium projectile fragments linearly. The averge multiplicity of target fragments decreases with the increasing of the number of helium projectile fragments which can be well expliained by the model of participant-spectator (the nuclear geometric model) of nucleus-nucleus interactions.
A two-step process for forming dibaryon (ΩΩ)0+ is studied. The first step is N+Ω→(NΩ)022+γ, or N+Ω→(NΩ)022+π,and the second step is an exchange reaction as:Ω+(NΩ)022→(ΩΩ)000+N. The results show that the cross sections of both steps are quite large,therefore this might be an important approach for producing (ΩΩ)0+.
Effect of the rotational degree of freedom of In nucleus in three dimension space on prescission particle emission in 10.6MeV/u and 8.5MeV/u 84Kr+27Al collisions was studied in the framework of a statistical model. The calculation results show that for the latter incident energy,particle emission is insensitive to the rotational degree of freedom,while for the former one,the incorporation of this factor leads to the reduction of the extracted fission delay time from 20×10－21s to 7.5×10－21s,indicating the existence of this effect. The result also demonstrates that this effect is unable to completely account for the experimental data. In addition,the effect of rotational degree of freedom on particle evaporation prior to scission was found to depend on the excitation energy.
A method to calculate reaction cross section based on the Glauber model is depicted in this paper. In the method, the density factor of Glauber model is modified and it is used to calculate the excitation function of proton-rich isotopes with same neutron number of n=3. Comparing the excitation function with experimental data, we found that, at above 100 MeV/u energies, the both excitation functions calculated by using the modified and the HO density factor are consistent very well with the experimental data. But, at the energies below 100MeV/u, the results calculated with modified density factor are close to the experimental data than that with HO distribution.
The HIJING 2.0 is used to generate Monte Carlo events for Au+Au minimum biased collisions at RHIC energies-sNN=130 and 200 GeV. Using the Monte Carlo event sample, it is shown that the impact parameter has approximately a linear dependence on multiplicity. Both of them can be used as characteristic quantity for centrality. The results on the /p ratio show that this ratio does not change remarkably with centrality, transverse momentum and rapidity, and is independent of the reaction plane within the HIJING model.
The progress and the on-line experimental results of isotope separator on-line in Lanzhou(ISOLAN) by using the low and the medium energy beams are described. The resolving power of ISOLAN is obtained to be 500\_700 for Xe by using FEBIAD ion source. The off-line overall efficiency is 3.1% for Krypton and 4.5% for Xenon. The on-line overall efficiency is 1.5%—2.0% for 104In,104Ag and 104Gd,and 5% for 199Hg. The isotopes of Hg,At and Rn produced in the bombardment of natural lead targets with 18O beam at 30MeV/u were successfully separated by ISOLAN. The highest energy of 1.234 MeV of γ-ray originated from the decay of 208Hg with a production cross-section of 5μb was observed.
The variational theory for general accelerating structure is studied in detail. The writer wishes to point out some errors in previous papers and explains some important points on the application of the variational expression.
Intense-leam proton linac sets a very severe requirement on the control of beam loss and emittance growth. Beam physics theory demonstrates that coupling of the strong space charge effect between different freedoms with different temperature will surely increase the beam emittance in the way of beam coherent instability. Therefore it is necessary to design an intense beam accelerator in accordance with the equipartitioning principle. However, this design is too tedious to reach full equipartitioning because the real proton linac is a quasi-periodic coupling system. Thus, we made a few modifications to TRACE3-D, which is a popular code in beam dynamics, and added the equipartitioning design function to it. When the modified TRACE3-D is used together with the PARMILA code, it is easy to realize equipartitioning. This paper will introduce the modification to TRACE3-D code, and then illustrate its application to the design of a DTL linac section, which shows the importance of equipartitioning design in the intense beam linac.
Compared with the method of one dimensional small angle X-ray scattering, two dimensional small angle X-ray scattering has the advantage of being able to study non-global symmetric system, thus to obtain the information about size and shape of particles (or holes) in oriented system. In this paper we report the establishment of a two dimensional synchrotron radiation small angle X-ray scattering device in Beijing Synchrotron Radiation Facility and the data analysis method developed. The results of an experiment on pitch-based carbon fiber with this device show the voids in pitch-based carbon fiber become larger as NH 3 content in the activator decreases in the activating process.
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