The influence of strongly coupled pickup channels on proton elastic scattering

We show that the influence of strongly coupled deuteron channels on proton elastic scattering is large. The effect is to increase the total reaction cross section by an amount which is several times the pickup cross section. The effect is particularly large for light nuclei suggesting a reason for the breakdown of the folding model for these nuclei. We have carried out model calculations which make these results plausible in terms of the deuteron acting as a doorway for proton absorption. The effect on the real potential is considerable for lighter nuclei and consistently repulsive. Results are also presented concerning the applicability of DWBA for pickup and which illuminate the adiabatic model of Johnson and Soper. Uncertainty in very low energy deuteron propagation makes the observation of experimental effects at (p, d) threshold somewhat doubtful.     

Proton spin-spin asymmetries for large angle electron-proton elastic scattering

Using the proper-time technique we calculate the one-fermion-loop contributions in four and six derivatives to the effective Lagrangian for theSU(2)xSU(2) non-linear σ-model.     

Strong coupling effects in near-barrier heavy-ion elastic scattering

Accurate elastic scattering angular distribution data measured at bombarding energies just above the Coulomb barrier have shapes that can markedly differ from or be the same as the expected classical Fresnel scattering pattern depending on the structure of the projectile, the target or both. Examples are given such as ¹⁸O + ¹⁸⁴W and ¹⁶O + ^{148, 152}Sm, where the expected rise above Rutherford scattering due to Coulomb-nuclear interference is damped by coupling to the target excited states, and the extreme case of ¹¹Li scattering, where coupling to the ⁹Li + n + n continuum leads to an elastic scattering shape that cannot be reproduced by any standard optical model parameter set. An early indication that the projectile structure can modify the elastic scattering angular distribution was the large vector analyzing powers observed in polarised ⁶Li scattering. The recent availability of high-quality ⁶He, ¹¹Li and ¹¹Be data provides further examples of the influence that coupling effects can have on elastic scattering. Conditions for strong projectile-target coupling effects are presented with special emphasis on the importance of the beam-target charge combination being large enough to bring about the strong coupling effects. Several measurements are proposed that can lead to further understanding of strong coupling effects by both inelastic excitation and nucleon transfer on near-barrier elastic scattering. A final note on the anomalous nature of ⁸B elastic scattering is presented as it possesses a more or less normal Fresnel scattering shape whereas one would a priori not expect this due to the very low breakup threshold of ⁸B . The special nature of ¹¹Li is presented as it is predicted that no matter how far above the Coulomb barrier the elastic scattering is measured, its shape will not appear as Fresnel like whereas the elastic scattering of all other loosely bound nuclei studied to date should eventually do so as the incident energy is increased, making both ⁸B and ¹¹Li truly “exotic”.     

Proton elastic scattering by nuclei: Fresnel and two-body correlation effects

In this paper we deal with the effects of Fresnel diffraction in the elastic scattering of 1 GeV protons by nuclei. Explicit expressions for the optical potential in⁵⁸Ni and²⁰⁸Pb are given, showing numerically that Fresnel effects and two-body correlations are of little importance in the elastic scattering of protons by nuclei.     

Proton polarizability contribution: Muonic hydrogen Lamb shift and elastic scattering

The uncertainty in the contribution to the Lamb shift in muonic hydrogen, ΔE^subt$\mathrm{\Delta }{E}^{\mathit{subt}}$ arising from proton polarizability effects in the two-photon exchange diagram at large virtual photon momenta is shown large enough to account for the proton radius puzzle. This is because ΔE^subt$\mathrm{\Delta }{E}^{\mathit{subt}}$ is determined by an integrand that falls very slowly with very large virtual photon momenta. We evaluate the necessary integral using a set of chosen form factors and also a dimensional regularization procedure which makes explicit the need for a low energy constant. The consequences of our two-photon exchange interaction for low-energy elastic lepton–proton scattering are evaluated and could be observable in a planned low energy lepton–proton scattering experiment planned to run at PSI.     

Virtual coupling potential for elastic scattering of Be on proton and carbon targets

The ^10,11Be(p, p) and (¹²C, ¹²C) reactions were analyzed to determine the influence of the weak binding energies of exotic nuclei on their interaction potential. The elastic cross sections were measured at GANIL in inverse kinematics using radioactive ^10,11Be beams produced at energies of 39.1A   and 38.4A MeV$38.4A\text{ MeV}$. The elastic proton scattering data were analyzed within the framework of the microscopic Jeukenne–Lejeune–Mahaux (JLM) nucleon–nucleus potential. The angular distributions are found to be best reproduced by reducing the real part of the microscopic optical potential, as a consequence of the coupling to the continuum. These effects modify deeply the elastic potential. Including the Virtual Coupling Potential (VCP), we show the ability of the general optical potentials to reproduce the data for scattering of unstable nuclei, using realistic densities. Finally, the concepts needed to develop a more general and microscopic approach of the VCP are discussed.     

Decoherence due to elastic Rayleigh scattering

We present theoretical and experimental studies of the decoherence of hyperfine ground-state superpositions due to elastic Rayleigh scattering of light off resonant with higher lying excited states. We demonstrate that under appropriate conditions, elastic Rayleigh scattering can be the dominant source of decoherence, contrary to previous discussions in the literature. We show that the elastic-scattering decoherence rate of a two-level system is given by the square of the difference between the elastic-scattering amplitudes for the two levels, and that for certain detunings of the light, the amplitudes can interfere constructively even when the elastic-scattering rates from the two levels are equal. We confirm this prediction through calculations and measurements of the total decoherence rate for a superposition of the valence electron spin levels in the ground state of 9Be+ in a 4.5?T magnetic field.     

Multiperipheralism and elastic scattering

Elastic scattering is calculated via unitarity, using a variety of multiperipheral models. Although special attention is paid to the effect of spinning cluster production, interference terms and phases, the forward elastic slopes thus calculated are still not consistent with experiment. An alternative type of dynamics is suggested.     

Proton polarization observables for the elastic and inelastic scattering of 500 MeV protons from Ca and Pb

Measurements for the elastic and inelastic scattering of 500 MeV protons from ⁴⁰Ca and ²⁰⁸Pb at small momentum transfers are reported. The induced proton polarization P and the spin rotation parameter Q were measured for the elastic scattering. The spin rotation parameters D_SS′, D_SL′, D_LL′, d_LS′ and the induced polarization P were measured for transitions to the 3⁻(3.37 MeV) and 5⁻(4.48 MeV) states in ⁴⁰Ca and the 3⁻(2.61 MeV) state in ²⁰⁸Pb. Comparisons of the data with the theoretical calculations were carried out in the framework of nonrelativistic and relativistic approaches. We extracted the spin-up and spin-down channels for the elastic scattering cross sections and found that predictions of the relativistic and nonrelativistic approaches agree well with the spin-up channel data and differ considerably in the spin-down channel.     

Two-photon-exchange correction to parity-violating elastic electron-proton scattering

Higher-order QED effects play an important role in precision measurements of nucleon elastic form factors in electron scattering. Here we introduce a two-photon-exchange QED correction to the parity-violating polarization asymmetry of elastic electron-proton scattering. We calculate this correction in the parton model using the formalism of generalized parton distributions, and demonstrate that it can reach several percent in certain kinematics, becoming comparable in size with existing experimental measurements of strange-quark effects in the proton neutral weak current.     

Relativistic light-cone approach to elastic electron-deuteron scattering

The connection between light-cone dynamics and field theory is analyzed in detail within the zero-range approximation, with particular attention to the so-called angular condition. New and detailed calculations for the elastic form factors of the deuteron are presented for the Bonn, Paris, Reid Soft-Core, Argonne V14 and one-pion-exchange potentials with various choices of the electromagnetic form factors of the nucleon.     

Contribution of statistical processes to elastic scattering

The sensitivity of the statistical theory to the choice of the distance-dependent transmittivity is investigated within the optical model. It is shown that for exponential density distributions, obtained in field theory, statistical scattering is negligibly small compared to diffraction. The alternating series appearing in the theory are summed rigorously. Some difficulties are noticed in comparing theory with experiment.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 17–21, June, 1971.We are grateful to V. M. Chudakov for discussing several problems of the statistical model.     

Four-body adiabatic model applied to elastic scattering

Elastic scattering of a projectile, composed of three clusters, from a spherical target is analysed using a four-body adiabatic model. The model is a generalisation of the three-body adiabatic model of Johnson and Soper. Calculations of the elastic scattering of ¹¹Li from ¹²C are compared to both experimental data and the results of recent four-body eikonal model calculations.     

Proton scattering at 1 GeV

The physics of 1-GeV proton scattering on nuclei is discussed in the light of recent calculations, and compared to the Gatchina, Los Alamos, and Saclay data. The impulse approximation (including spin-orbit effects and correlations) is reviewed, and comparison is made with other theories such as the Glauber model and the low-energy optical model. This discussion is addressed to specialists as well as nonspecialists in the field. The neutron distribution is extracted from the data and a detailed comparison is made with other determinations of this distribution and with the Hartree-Fock predictions. The neutron radii are seen to be generally larger than the proton radii. Within a given shell, they increase at a much slower rate ($\text{～A}{}^{\mathrm{<mtext>1</mtext><mtext>8</mtext>}}$) than the $\text{A}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ rule. Except possibly for ²⁰⁸Pb, they are consistent with the Hartree-Fock predictions, but not with the values obtained from Coulomb energies. The study of inelastic scattering to collective states allows the extraction of neutron transition densities, and in particular the analog B(N, L) of the electromagnetic transition rates B(E, L) one usually considers for the protons. Neutron excitations are seen to be stronger by 20 to 40 % than proton excitation, exceeding the $\text{N}\text{Z}$ prediction of the collective model. Spin effects lead only to small changes in the cross section, but to a measurable analyzing power. The unnatural parity excitations of the lowest 2^? (T = 0) state of ¹⁶O and the 1⁺ (T = 1) state of ¹²C show that the spin-spin and tensor terms of the nucleon-nucleon amplitude are sizable. Their relative magnitudes are seen to be crucial for explaining the observed cross sections.