Multiple scattering effect for quasifree scattering in the 3He(p,pp)2H reaction at 64.8 MeV

For the ³He(p, pp)²H reaction at 64.8 MeV, angular correlations have been measured in the quasifree scattering region. Angular dependence of the ratio of the cross sections measured to those calculated in the plane-wave impulse approximation is well reproduced by a calculation taking account of the double-scattering effect.     

Final state interactions in nuclear pion photoproduction over the (3, 3) resonance

An impulse approximation calculation is made on the reaction ⁵¹V(γ, π⁺)⁵¹Ti from the region just above photopion threshold to the tail of the (3, 3) resonance. Pion final state distortions are taken into account through realistic optical potentials. Results are compared to those for plane-wave and surface-produced pions and to recent experiment. Comparison is made between surface-produced pions and pions distorted by the s-wave component of the optical potential.     

Charged pion photoproduction from 10B and 13C

Positive and negative pion photoproduction cross sections from ¹⁰B and ¹³C leading to the ground state of the residual nucleus have been calculated in the plane-wave and distorted-wave impulse approximations. The results are compared with experiment and with other theoretical calculations. While a large discrepancy is observed between experiment and theory in the case of negative pion photoproduction from ¹³C, fair agreement is obtained between experiment and the plane-wave calculations in all other reactions. It is found that in all reactions studied, except in the case of positive pion production from ¹³C, the inclusion of the pion-wave distortions moves the theory away from the experimental points. It is also found that the photopion differential-cross-section calculations show a sensitivity to the nuclear wave function different from that predicted by the electron scattering form-factor calculations.     

Investigation of the Li (e,e′p) reaction at 1200 MeV

The reaction ⁶Li (e, e′p)⁵He has been investigated with a resolution good enough to distinguish the effects of the s- and p-shells of the ⁶Li nucleus. The reaction cross section has been measured as a function of the missing energy from −15 to +30 MeV. The proton angular distribution has been measured at missing energies of 4 and 20 MeV. The comparison of the data with calculations within the framework of the plane-wave impulse approximation gives the harmonic oscillator parameters q_p = 50 ± 5 MeV/c,q_s = 108 ± 9 MeV/c.     

Study of relativistic bound state wave functions in quasielastic (e,e′ p) reactions

The unpolarized response functions of the quasielastic ¹⁶O(e,e′ p)¹⁵N reaction are calculated for three different types of relativistic bound-state wave functions. The wave functions are obtained from relativistic Hartree, relativistic Hartree-Fock and density-dependent relativistic Hartree calculations that reproduce the experimental rms charge radius of ¹⁶O. The sensitivity of the unpolarized response functions to the single-particle structure of the different models is investigated in the relativistic plane-wave impulse approximation. Redistributions of the momentum dependence in the longitudinal and transverse response function can be related to the binding energy of the single-particle states. The interference responses R_LT and R_TT reveal a strong sensitivity to the small component of the relativistic bound-state wave function.     

alpha-cluster wave functions for 9be from the 9Be(p,pα)5He reaction between 35 and 160 MeV

We have used harmonic-oscillator, Hulthén, square-well and Woods-Saxon wave functions in an attempt to describe the ⁹Be(p, pα)⁵He reaction in the context of the plane-wave impulse approximation (PWIA) with radial cut-off. We have obtained reasonable fits to all the data between 35 and 160 MeV by using the Woods-Saxon wave functions, and increasing the cut-off radius for decreasing energy. A consistent value for the effective number of α-clusters in ⁹Be was obtained and found to be 0.2.     

Neutron Transverse-Momentum Distributions and Polarized 3He within Light-Front Hamiltonian Dynamics

The possibility to extract the quark transverse-momentum distributions in the neutron from semi-inclusive deep inelastic electron scattering off polarized ³He is illustrated through an impulse approximation analysis in the Bjorken limit. The generalization of the analysis at finite momentum transfers in a Poincaré covariant framework is outlined. The definition of the light-front spin-dependent spectral function of a J = 1/2 system allows us to show that within the light-front dynamics only three of the six leading twist T-even transverse-momentum distributions are independent.     

Effects of nuclear deformation in quasi-elastic electron scattering

We discuss effects due to nuclear deformation that can be observed in quasi-elastic electron scattering from deformed nuclei. To simplify the discussion we restrict ourselves to the plane wave impulse approximation (PWIA) and compare the form of the spectral function for axially symmetric deformed nuclei with that for spherical nuclei in the independent particle model. We point out that a strong dependence on deformation can be expected for momentum distributions measured in narrow missing energy ranges. This is illustrated taking ²⁸Si as an example.     

The 6Li(α, 2α)2H reaction at 700 MeV and the α-d momentum distribution

The results of an experimental study of the reaction ⁶Li(α, 2α)²H at 700 MeV are given. A comparison with the data from seven other reactions pertaining to the α⁺d cluster structure of ⁶Li is presented. The amplitude for the virtual transition ⁶Li→α+d obtained three of these experiments and the present one are comparable. The internal momentum distributions extracted with the plane-wave impulse approximation in four of the experiments are compatible with a pole form, the width parameter being given by the α-separation energy in ⁶Li. The remarkable consistency among these results is seen as evidence for the validity of the simple models used for both the reaction mechanism (PWIA) and to describe the α d-vertex (pole approximation) in ⁶Li.     

Superscaling in charged current neutrino quasielastic scattering in the relativistic impulse approximation

Superscaling of the quasielastic cross section in charged-current neutrino-nucleus reactions at energies of a few GeV is investigated within the framework of the relativistic impulse approximation. Several approaches are used to describe final-state interactions and comparisons are made with the plane-wave approximation. Superscaling is very successful in all cases. The scaling function obtained using a relativistic mean field for the final states shows an asymmetric shape with a long tail extending towards positive values of the scaling variable, in excellent agreement with the behavior presented by the experimental scaling function.     

Quasi-free scattering in the 6Li(d,dα)2H reaction at 52 MeV

In order to study the momentum distribution of an α-cluster in ⁶Li we have investigated the quasi-free scattering of deuterons in the ⁶Li(d, dα)²H reaction, using 52 MeV deuterons. The α-particle detector was kept at a fixed position of 30° and the second detector scanned over a range of coplanar angles. The α-cluster momentum distribution has been extracted by means of the plane-wave impulse approximation, using both the energy-sharing method and the angular correlation method. The momentum distributions so obtained are in good agreement with those obtained from other reactions such as (p, pα) and (α, 2α), and are compared with the spectator model. The reasons why the model works well are discussed. For the first time, to our knowledge, quasi-free scattering of deuterons on an α-cluster of a nucleus has been measured and analysed.     

Multiple scattering effects for quasifree scattering in 3He(d,dd)1H breakup reaction

The differential cross sections for the ³He(d, dd)¹H breakup reaction have been measured in the kinematical region corresponding to quasifree scattering (QFS). The angular dependence of the cross section at the minimum laboratory energy of the unobserved proton has been obtained. The shapes of energy spectra are approximately reproduced by a calculation in the plane-wave impulse approximation (PWIA). As for the angular dependence of the cross section and for the absolute values, the calculation fails to reproduce the experimental results. A calculation with multiple scattering effects reproduces the experimental data well, not only for the shape of the energy spectra but also for the angular dependence. For the absolute cross sections, the ratio of the experimental values to the calculated ones with multiple scattering effects is 0.7 and this value is improved compared with the value of 0.3 obtained by the PWIA calculation.     

Quasi-elastic electron scattering on 3He

Quasi-elastic electron from ³He is calculated in the framework of impulse approximation as a test of a ground state wave function calculated from the Reid soft-core interaction with the Faddeev technique. A comparison with high momentum transfer electron scattering data is made.     

Measurement of the tensor A yy and vector A y analyzing powers of the deuteron inelastic scattering of beryllium at 5.0 GeV/c and 178 mrad

Tensor A _yy and vector A _y analyzing powers in the inelastic scattering of deuterons with a momentum of 5.0 GeV/c on beryllium at an angle of 178 mrad in the vicinity of the excitation of baryonic resonances with masses up to ～ 1.8 GeV/c ² have been measured. The A _yy data are in good agreement with the previous data obtained at 4.5 and 5.5 GeV/c. The results of the experiment are compared with the predictions of the plane-wave impulse approximation and ω meson-exchange models.     

The reactions 6, 7Li, 9Be, 10B(e,e′p) at 700 MeV and DWIA analysis

The proton spectral functions of ⁶Li, ⁷Li, ⁹Be and ¹⁰B obtained from the (e, e′p) reactions at 700 MeV are presented. The results were analyzed in the distorted-wave impulse approximation, using the shell-model single-particle wave functions consistent with the elastic electron scattering results. The observed Ip proton momentum distributions for the nuclei ⁶Li, ⁷Li and ⁹Be show significant disagreement with the shell-model momentum distributions. The occupation probabilities of the proton single-particle states are around 0.7, with a few exceptions.     

Electron-phonon interaction in a free standing beryllium monolayer

We report ab initio study of the electron-phonon coupling in a free standing Beryllium monolayer. The calculations were carried out using a linear-response approach in the plane-wave pseudopotential representation. The Eliashberg spectral function α²F(ω) and the electron-phonon coupling parameter λ are evaluated at the Fermi level. The obtained results show a large contribution to the electron-phonon coupling from the low-energy transverse mode scattering.     

On the Li(p,pt)He reaction

Using a cluster model, the reaction ⁷Li(p, pt)⁴He has been analysed in the distorted-wave impulse approximation. All exchange terms arising from antisymmetrization of the target wave function have been calculated. When the correct asymptotic form for the intercluster wave function is used, the magnitude and shape of the measured angular correlation are reproduced both at 156 and 55 MeV. The analysis indicates that ⁷Li in its ground state is strongly clustered.     

The use of quasielastic pion-proton backward scattering at 0.7 GeV/c for studying Fermi motion in light nuclei

The plane-wave approximation was used to examine the proton Fermi-momentum distribution in experiments on quasielastic large-momentum-transfer pion-nucleon scattering in light nuclei ⁶Li, ⁷Li, and ¹²C. It was found that, unlike the (e, e′) reaction, the Fermi-gas model is in poor agreement with experiment, whereas the oscillator model adequately describes the spectrum shape. However, the parameters obtained for these distributions are sizably smaller than those derived from the (e, e′)) experiments. This suggests that the plane-wave approach is inadequate and that more complicated theoretical approaches, supposedly allowing for pion-nucleon amplitude modification in nuclear matter, are necessary for the analysis of experimental data.     

Momentum distributions in A = 3 and 4 nuclei

We develop a general Monte Carlo method to study momentum distributions of nucleons and nucleon clusters in nuclei. The method is used to calculate the momentum distributions of protons and neutrons in A = 3 and 4, d + p amplitudes in ³He, and t + p and d + d amplitudes in ⁴He nuclei, with improved variational wave functions. The nucleon and d + p momentum distributions in ³He are also calculated from a five-channel Faddeev wave function. The calculations are based on realistic hamiltonians that include the three-nucleon interaction, and give reasonable binding energies and densities for light nuclei and nuclear matter. The calculated proton and d + p momentum distributions in ³He at low k are in good agreement with the results obtained by the Saclay analysis of the electron scattering data in the plane-wave impulse approximation; however, at higher values of k, the calculated momentum distributions are larger. The calculated values of the asymptotic D- to S-wave ratio of the d+n and d+d amplitudes are also in agreement with the values obtained from (d, t) and (d, α) reactions. The number of deuterons is found to be 1.38 and ∼2.4 in A = 3 and 4 nuclei, while the number of tritons in ⁴He is ∼1.6. This large value of the triton number reflects the large contribution (more than 90% at small k) of the t+p state to the total proton momentum distribution in ⁴He.     

Nuclear mass form factors from coherent photoproduction of πmesons

Data for coherent photoproduction of π⁰ mesons from nuclei ( ¹²C, ⁴⁰Ca, ⁹³Nb, ^natPb), recently measured with the TAPS detector at the Mainz MAMI accelerator, have been analyzed in view of the mass form factors of the nuclei. The form factors have been extracted in plane-wave approximation of the A(γ,π⁰)A reaction and corrected for final-state interaction effects with the help of distorted-wave impulse approximations. Nuclear mass rms radii have been calculated from the slope of the form factors for q² → 0. Furthermore, the Helm model (hard-sphere form factor folded with Gaussian) was used to extract diffraction radii from the zeroes of the form factor and skin thicknesses from the position and height of its first maximum. The diffraction radii from the Helm model agree with the corresponding charge radii obtained from electron scattering experiments within their uncertainties of a few per cent. The rms radii from the slope of the form factors are systematically lower by up to 5% for PWIA and up to 10% for DWIA. Also the skin thicknesses extracted from the Helm model are systematically smaller than their charge counterparts.