Effect of meson exchange corrections on allowed muon capture

Corrections to the impulse approximation calculation of the γ?ν angular correlation coefficient and recoil nuclear polarization in allowed muon capture transitions, arising from meson exchange effects, are studied and the value for the induced pseudoscalar coupling consistent with both observables is found to be (13.3 + 3)_gA, to a large extent free from nuclear wave function uncertainties.     

An eikonal treatment including two-step mechanisms for the (p,n) reaction on light nuclei

The reactions ⁷Li(p, n)⁷Be(g.s.), ⁷Li(p, n)⁷Be(0.43 MeV), and ¹³C(p, n)¹³N(g.s.) are treated in an eikonalized distorted-wave impulse approximation (DWIA), including the contribution of a two-step mechanism involving isovector correlations for the last reaction. Our calculation uses the free on-shell nucleon-nucleon t-matrix, with spin and isospin dependence, and incorporates antisymmetrization of it. We find agreement at roughly the 20% level with the forward experimental charge-exchange results in the energy range 120 to 200 MeV. The two-step contribution for the ¹³C case is rather small, being of the order of 10% at 0°; it interferes constructively, thus improving somewhat the agreement with experiment.     

Pion single charge-exchange reaction on nuclei near the (3, 3) resonance

Angle integrated cross-sections for the pion single charge-exchange reaction on¹³C and⁷Li have been calculated at several energies in the distorted wave impulse approximation employing the off-shell nature of the pion-nucleon scattering amplitude and using the Breit-Wigner formula for its energy dependence. Effect of the two nucleon correlations in the nucleus on the cross-section is also studied. Our results are in rough accord with the experimental data. The major part of this work was done while the author was at the University of Manitoba, Canada.     

Chiral unitary approach to the K–deuteron scattering length

Starting from a recent model where the amplitudes are evaluated from the chiral Lagrangians using a coupled-channel unitary method, we evaluate here the scattering length for K⁻–deuteron scattering. We find that the double scattering contribution is very large compared to the impulse approximation and that the charge-exchange contribution of this rescattering is as large as the sequential K⁻ scattering on the two nucleons. Higher-order rescattering corrections are evaluated using coupled channels with K⁻ and within the integral form of the fixed centre approximation to the Faddeev equations. The higher-order corrections involving intermediate pions and hyperons are found negligible.     

Polarization transfer in the 4He(e-->,e'p-->)3H reaction up to Q2=2.6 (GeV/c)2

We have measured the proton recoil polarization in the 4He(e-->,e(')p-->)4H reaction at Q(2)=0.5, 1.0, 1.6, and 2.6 (GeV/c)(2). The measured ratio of polarization transfer coefficients differs from a fully relativistic calculation, favoring the inclusion of a medium modification of the proton form factors predicted by a quark-meson coupling model. In addition, the measured induced polarizations agree reasonably well with the fully relativistic calculation indicating that the treatment of final-state interactions is under control.     

Polarization effects in inelastic deuteron scattering in the region of baryon-resonance excitation

Within the impulse approximation, polarization effects in inelastic deuteron scattering on nuclei are investigated in the region around the resonance of mass about 2190 MeV/c ². It is shown that the spin-dependent part of the NN → NN*(2190) amplitude plays a significant role at high momentum transfers. Predictions are obtained for some polarization observables and cross sections for various deuteron-spin-flip processes.     

Ab initio many-body calculations of the (3)H(d,n)(4)He and (3)He(d,p)(4)He fusion reactions

We apply the ab initio no-core shell model combined with the resonating-group method approach to calculate the cross sections of the (3)H(d,n)(4)He and (3)He(d,p)(4)He fusion reactions. These are important reactions for the big bang nucleosynthesis and the future of energy generation on Earth. Starting from a selected similarity-transformed chiral nucleon-nucleon interaction that accurately describes two-nucleon data, we performed many-body calculations that predict the S factor of both reactions. Virtual three-body breakup effects are obtained by including excited pseudostates of the deuteron in the calculation. Our results are in satisfactory agreement with experimental data and pave the way for microscopic investigations of polarization and electron-screening effects, of the (3)H(d,γn)(4)He bremsstrahlung and other reactions relevant to fusion research.     

Compton scattering of an X-ray photon by an open-shell atom

A nonrelativistic quantum theory for the nonresonant Compton scattering of an X-ray photon by a free many-electron atom with an open shell in the ground state has been constructed in the single-configuration Hartree-Fock approximation outside the impulse approximation widely used in the literature. The transition to an atom with closed shells reproduces the results obtained previously in [6, 7]. The results of a test calculation for atoms with open (Ti, Fe) and closed (Zn) 3d core shells are presented. The effects of the radial relaxation of one-electron states in the field of core vacancies have been taken into account. The results of the calculation agree well with the experimental results [15, 16]. It has been established that the results of the impulse approximation in the investigated X-ray photon energy ranges disagree with those of our theory not only quantitatively but also qualitatively. In particular, the impulse approximation near the elastic (Thomson and Rayleigh) scattering line leads to a gross overestimation of the contributions from the deep atomic shells involved in the inelastic photon scattering only virtually to the scattering probability. The presented theory is general in character and its applicability to a particular element of the Mendeleev table with an open core shell or to a many-electron atomic ion is limited only by the requirement that the nonrelativistic Hartree-Fock approximation be properly used in describing the scattering-state wave functions.     

Excited states of muonium in atomic hydrogen

Muonium formation in excited states in muon-hydrogen charge-exchange collision is investigated using a method developed in a previous paper. Differential cross-section results are found to resemble positronium formation cross-section results of positron—hydrogen charge-exchange problem. Forward differential and integrated cross-sections are computed for muon energy of 2 keV and higher. Total muonium formation cross-sections are computed using Jackson and Schiff scaling rules. Muonium formation cross-section results obtained from proton—hydrogen charge-exchange cross-section results, using velocity scaling are compared with the results of the present calculation     

电子碰撞原子(e,2e)反应的复极化势

研究包括连续通道等非处理通道的复极化势对(e,2e)碰撞过程三重微分截面的影响,即将耦合通道光学势方法得到的复极化势附加到畸变波玻恩近似方法的畸变势中,在靶态的HF近似下,计算了Ar原子和Ne原子在非共面对称几何条件下(e,2e)反应的三重微分截面.对于较高的入射能量,在实验的误差范围内,计算结果与电子动量谱的实验数据符合较好,复极化势的影响很小;对于较低的入射能量,复极化势的作用明显增大. 关键词： 复极化势 (e;2e)反应 三重微分截面 电子动量谱     

Spin-polarized tunneling spectroscopy of co(0001) surface States

Spin-polarized tunneling was studied on Co surfaces of exchange coupled Co/Cu/Co samples, using an Fe tip. A spin-polarized surface state of Co(0001) was found to exist at -0.43 eV relative to E(F), with FWHM of 0.23 eV in the spectra. The state exhibits negative magnetoresistance with an effective spin polarization of less than -23%, suggesting negatively high spin polarization of the surface state. Our first-principles calculations have supported the existence of the surface state. From the calculation, the state is identified as a minority spin Gamma-centered d(2)(z)-like surface state.     

The Implementation of Impulse Approximation in the Wave Function and the Response Function of Many-Fermion System

In this work, we investigate the ambiguities proposed by Benhar et al. about different implementation of the impulse approximation (IA) for calculation of the response function of many-Fermion system. The many-Fermion wave-function of composite system is calculated in the framework of impulse approximation by considering the iteration equation of many-Fermion wave-function through the system Hamiltonian propagator, and it is shown that by imposing the plane wave approximation for the struck particle it is possible to remove these ambiguities (the plane wave impulse approximation (PWIA)). Finally it is concluded that in order to get relevant result, one should be careful to perform the IA on the many-Fermion wave function to calculate the response function of the system, since the system response is obviously very sensitive to this quantity.     

在格点上构造计算胶球质量的新途径

发展了一种为了计算胶球质量而构造格点算符的新途径.基于所选用算符的连续极限与状态量子数JPC两者之间的联系,状态的自旋就可以在数值模拟中唯一和直接地被确定下来.进而,这一途径可以被应用于计算任意自旋J的胶球质量.在淬火近似下,给出在SU(3)纯规范场中0⁺⁺态和2⁺⁺态胶球质量的初步结果,它们分别是1754(85)(86)MeV和2417(56)(117)MeV.     

Green's function calculations of the hyperfine interaction for impurities in metals andfor metallic interfaces

We present local density functional calculations for magnetic impurities andmagnetic monolayers in non-magnetic metals. The calculations employ a multiple scattering (KKR) Green's function method for impurities in the bulk andfor ideal surfaces and interfaces. In particular we discuss the moment formation of 3d and4d impurities in alkali andnoble metals. Special emphasis is put on an accurate calculation of the host polarization around 3d impurities in Cu andPd. While the calculated impurity hyperfine fields in Cu contain rather large errors due to the local density approximation, the induced fields of the Cu atoms agree very well with experiments. We also present similar calculations for magnetic monolayers andthe corre-sponding induced host polarization in Cu andPd.     

Dynamical relativistic effects in quasielastic 1p-shell proton knockout from 16O

We have measured the cross section for quasielastic 1p-shell proton knockout in the 16O(e,e(')p) reaction at omega = 0.439 GeV and Q2 = 0.8 (GeV/c)(2) for missing momentum P(miss)相似文献   

The Dirac distorted wave impulse approximation revisited

Recently, we have proposed a new interpretation of the successful Dirac approach to protonnucleus elastic scattering, based on relativistic kinematics and the Lorentz-Lorenz correction. Here, we show that the Dirac distorted wave impulse approximation for low-lying collective states can be understood along the same lines. This confirms our view that relativistic effects are not the only possible explanation of the polarization data at intermediate energies.     

Extracting nuclear transparency from p,2p-A and e,e′p-A cross sections

We study nuclear-structure effects on the transparency in high-transverse-momentum (p,2p) and (e,e′p) reactions. We show that in the eikonal-distorted-wave impulse approximation (EDWIA), even when correlations are included, one can get a factorized expression for the transparency which depends only on the average nucleon density (r) and a correlation function. A technique is developed to include correlations in a Glauber calculation, where we use a Monte Carlo method for integration over the nuclear coordinates. We compare calculations of T using the EDWIA formalism, and a continuous density, with a Monte Carlo method based on discrete nucleons.     

Calculation of lower excited electronic levels of benzene with the Green's function method

The Green's function method for the calculation of orbital energies which was discussed in a preceding paper is applied to the calculation of the lower excited states of the benzene molecule. The Dyson equation for the polarization (particle—hole) propagator is derived with the diagrammatic technique and the secular equation which gives poles of the polarization propagator is solved. The random phase approximation is not used in our calculation. Theoretical results are discussed in comparison with experimental data. Using a model system of two π-electrons, our method is compared with the equations-of-motion method.     

Polarization in charge exchange reaction π−+p→π0+n at 40 GeV/c for the 4-momentum transfer range 0<|t|<2 (GeV/c)2

The results on measuring polarization in charge exchange reaction π^?+p→π⁰+n at 40 GeV/c are presented for the 4-momentum transfer range from 0 up to 2 (GeV/c)². At |t|≦0.4 (GeV/c)² the polarization has a positive sign. In the “crossover” region of π^± elastic scattering a possible minimum in the polarization behaviour has been seen for the first time. the polarization is zero within the statistical accuracy near this point. In the “deep” region of the charge-exchange differential cross-section the polarization has a negative sign. The presented data are not in agreement with the modern theoretical models.