Pionization effects in nucleon-nucleus scattering

A simple unitary model for meson production in nucleon-nucleon scattering is extended to nucleon-nucleus scattering. In the high energy limit the produced mesons remain coherent with the projectile over the entire depth of the nucleus and tend to increase the total cross sections. A crude estimate of the size of the effect gives an increase of the total cross section for proton-deuteron scattering of 13 mb at NAL energies.     

Nonrelativistic description of nucleon-nucleus scattering

Within the three-dimensional semiclassical approximation, an analytic expression is obtained for the amplitude of proton-nucleus scattering at intermediate energies of incident protons. The method for deriving this amplitude is based on the use of the high-energy approximation with distorted waves. In view of the short-range character of proton-nucleon interaction, the process of proton-nucleus scattering is represented as a series of single scattering events occurring on each individual nucleon. With the aid of the proposed mathematical formalism, a recursion relation is derived that makes it possible to express the nuclear form factor obtained within the distorted-wave method in terms of the sum of an infinite Born series. Parameters that characterize the distributions of protons and neutrons in the spherical nuclei ⁴⁰Ca, ⁴⁸Ca, ⁹⁰Zr, and ²⁰⁸Pb and which include the width of the surface layer of nucleons and the root-meansquare radii of the proton-, neutron-, and nucleon-density distributions are determined from an analysis of the measured cross sections for the elastic scattering of 1-GeV protons, a modified Fermi function being employed for the nucleon-density distribution.     

Fluctuations and double nucleon-nucleus scattering

We analyze a Gedankenexperiment of a double nucleon-nucleus scattering and we find that the measurement of the corresponding cross section averaged over a broad energy interval determines the correlation function. This possibly could be applied for the experimental study of fluctuations at very heavy elements.     

Description of nucleon-nucleus scattering in the Dirac-Brueckner method

Elastic scattering of protons from nuclei is studied based on the Dirac-Brueckner approach. Effective N-N interactions in the nuclear medium are obtained by solving the relativistic Brueckner-Bethe-Goldstone equation in infinite nuclear matter. Relativistic optical potentials for p-⁴⁰Ca scattering at 200 MeV are calculated in the improved local density approximation. It is found that medium effects other than Pauli blocking reduce the strengths of scalar and vector potentials very much. Differential cross section and spin observables are calculated and compared with experimental data.     

Theory of two-step processes for nucleon-nucleus scattering

The basis of the conventional formula for the two-step-process approximation (TSPA) is discussed in terms of three-body collisions for the inelastic scattering of a nucleon by a heavy nucleus and the accompanying charge-exchange reactions. A criterion is obtained for determining the effective interaction of the first term of the TSPA and the reaction processes that should be explicitly taken into account in the second term. The applicability of the TSPA for estimating the effects of intermediate states, in which a pair of constituent particles is in a resonant state or in a virtual state, is also discussed.     

Predicting total reaction cross sections for nucleon-nucleus scattering

Nucleon total reaction and neutron total cross sections to 300 MeV for 12C and 208Pb, and for 65 MeV scattering spanning the mass range, are predicted using coordinate space optical potentials formed by full folding of effective nucleon-nucleon interactions with realistic nuclear ground state densities. Good to excellent agreement is found with existing data.     

A multichannel quasi-separable potential approach to nucleon-nucleus scattering

A quasi-separable potential model for two-body multichannel scattering is developed. Spin and Coulomb effects are taken into account. By a suitable choice of the separable nuclear interactions we arrive at simple analytic expressions for the transition amplitudes. Our model is applied to the study of the n-¹²C and p-¹²C scattering processes. Effects arising from the excitation of the target nucleus are well reproduced.     

Spin-orbit and Pauli-correlation effects in intermediate-energy proton-nucleus inelastic scattering

The excitation of the 3^? (6.13 MeV) state of ¹⁶O by 0.8 GeV protons is studied using Glauber theory with a spin-orbit NN amplitude. Two previously suggested approaches for handling the z-ordered non-commuting NN profile functions, γ, are compared and found to give nearly identical results for the usual observables. Transitions to certain LM substates which are forbidden in one approach are allowed in the other, but their cross sections are proportional to the fourth power of the strength of the NN spin-orbit amplitude and thus quite small. It is also shown that, in this energy region, an expansion in powers of the strength of the spin-orbit interaction converges rapidly and consequently any convenient ordering of the γ's can be used without serious errors. Using this result an estimate of the effects of Pauli correlations on the cross section and the polarization is given.     

On relativistic and non-relativistic approaches to nucleon-nucleus scattering

The impulse approximation to the Dirac theory of nucleon-nucleus scattering is reduced to a non-relativistic formalism. It is shown that relativistic effects can be included on the same footing as the effects of the nuclear medium on the effective interaction. We apply the argument to spin observables in 200 MeV and 500 MeV proton elastic scattering on a ⁴⁰Ca target.     

Relativistic time delays in the Dirac approach to nucleon-nucleus scattering

In connection with a characteristic feature of the effective optical potential in the Dirac approach two types of time delays are considered in the relativistic eikonal approximation. One is obtained from the scattering amplitude and the other given by the wave packet motion in the interaction region. These time delays turn out to differ in sign at intermediate energies, in contrast to the agreement between corresponding nonrelativistic time delays.     

Medium corrections to the reaction cross section for low energy pion4He scattering

We investigate the effects of the Pauli principle and the nucleon binding on the reactive content of the single scattering optical potential. The binding and exclusion principle effects are calculated for low energy pion-⁴He scattering. A careful treatment of the Pauli principle enables us to determine a pion nucleon energy shift representing binding effects from the requirement that the reaction channel opens at the correct threshold energy. We find that binding and Pauli effects lead to a reduction of the reaction cross section by about 30–50% and (expect for very low energies) to a slight increase of the elastic cross section by 5–10%.     

Some aspects of redundant states in nucleon-nucleus scattering solutions with antisymmetrization

Redundant states are known to appear as solutions to the scattering equation when an incident particle is antisymmetrized with respect to a target nucleus represented by a Slater determinant. Using criteria which have been found to characterize a potential which produces a continuum bound state (CBS), we demonstrate that a redundant solution can be identified as a CBS which appears at every positive energy. This identification provides a procedure for isolating and removing that portion of the potential responsible for redundant states. The remaining portion of the potential generates solutions to the original scattering equation which we demonstrate to be orthogonal to the redundant states which have been eliminated.     

Two-loop corrections to Bhabha scattering

The two-loop radiative photonic corrections to Bhabha scattering are computed in the leading order of the small electron mass expansion up to the nonlogarithmic term. After including the soft photon bremsstrahlung, we obtain the infrared-finite result for the differential cross section, which can directly be applied to a precise luminosity determination of the present and future e+ e- colliders.     

Local and nonlocal space-like fields in the relativistic description of nucleon-nucleus scattering

It is shown that a local complex space-like nucleon-nucleus potential does not influence the observables associated with the elastic scattering, in contrast to a nonlocal space-like potential obtained from nuclear matter via a local density approximation. In order to eliminate the nonlocal space-like field, new scalar and time-like local components are defined. The energy dependence of the ratio of the strengths of the real parts of these two quantities is investigated.     

Electromagnetic radiative corrections in parity-violating electron-proton scattering

QED radiative corrections have been calculated for leptonic and hadronic variables in parity-violating elastic ep scattering. For the first time, the calculation of the asymmetry in the elastic radiative tail is performed without the peaking-approximation assumption in hadronic variables configuration. This method has been validated in a comparison with the PVA4 data. It has been also used to evaluate the radiative corrections to the parity-violating asymmetry measured in the G⁰ experiment. The results obtained are here presented.     

Medium corrections to the first order optical potential for low-energy pion-4He scattering

We study the Pauli-principle corrections for low energy π-⁴He elastic scattering. In our approach we take into account explicitly the spin and isospin dependence of the Pauli-principle effect. Furthermore we discuss the combined effect of the Pauli-principle correction and the nuclear binding. Contrary to the Pauli principle we treat the binding corrections in an approximate way, using an effective mass for the residual nucleus. In our calculations we use the first-order optical potential of Celenza, Liu and Shakin. The Pauli-principle correction is found to have a considerable effect on the differential cross section. Our results indicate that the Pauli-principle corrections are largely compensated by the nuclear binding.