Relativistic predictions of exclusive 208Pb(p⃗,2p)207Tℓ^{208}Pb(\vec{p},2p) ^{207}T\ell analyzing powers at an incident energy of 202 MeV

Within the framework of the relativistic distorted wave impulse approximation (DWIA), we investigate the sensitivity of the analyzing power - for exclusive proton knockout from the 3s$_{1/2}$, 2d$_{3/2}$ and 2d$_{5/2}$ states in $^{208}$Pb, at an incident laboratory kinetic energy of 202 MeV, and for coincident coplanar scattering angles ($28.0^{\circ}$, $-54.6^{\circ}$) - to different distorting optical potentials, finite-range (FR) versus zero-range (ZR) approximations to the DWIA, as well as medium-modified coupling constants and meson masses. Results are also compared to the nonrelativistic DWIA predictions based on the Schr\"{o}dinger equation. Whereas the nonrelativistic model fails severely, both ZR and FR relativistic DWIA models provide an excellent description of the data. For the FR predictions, it is necessary to invoke a 20% reduction of sigma-nucleon and omega-nucleon coupling constants as well as for $\sigma$-, $\rho$- and $\omega$-meson masses, by the nuclear medium. On the other hand, the ZR predictions suggest that the strong interaction in the nuclear medium is adequately represented by the free nucleon-nucleon interaction associated with the impulse approximation. We also demonstrate that, although the analyzing power is relatively insensitive to the use different relativistic global optical potential parameter sets, the prominent oscillatory behavior of this observable is largely attributed to distortion of the scattering wave functions relative to their plane wave values.Comment: 16 pages, 3 figures, submitted to Phys. Rev.

Relativistic predictions of spin observables for exclusive proton knockout reactions

Within the framework of the relativistic distorted wave impulse approximation (DWIA), we investigate the sensitivity of complete sets of polarization transfer observables for exclusive proton knockout from the 3s$_{1/2}$, 2d$_{3/2}$ and 2d$_{5/2}$ states in $^{208}$Pb, at an incident laboratory kinetic energy of 202 MeV, and for coincident coplanar scattering angles ($28.0^{\circ}$, $-54.6^{\circ}$), to different distorting optical potentials, finite-range (FR) versus zero-range (ZR) approximations to the DWIA, as well as medium-modified meson-nucleon coupling constants and meson masses. Results are also compared to the nonrelativistic DWIA predictions based on the Schr\"{o}dinger equation.Comment: Submitted for publication to Physicical Review C, 23 pages, 7 figure

Influence of relativistic dynamics and density-dependent corrections on the induced polarization and analyzing power for exclusive 1s1/2 proton knockout in C12

Induced polarization and analyzing power data for exclusive proton-induced proton knockout from the 1s1/2-state in C12-at incident energies of 392 MeV and 1 GeV and for kinematics corresponding to zero recoil momentum-are studied within the framework of both relativistic and nonrelativistic distorted wave models based on the impulse approximation. We also study to which extent relativistic dynamical effects can be simulated in the nonrelativistic Schrödinger-equation-based distorted wave model via the introduction of effective nucleon mass corrections (within the context of the Walecka model of quantum hadrodynamics) to the nucleon-nucleon (NN) scattering matrix. A quantitative description of the data is achieved by invoking density-dependent corrections to the NN amplitudes within the framework of our relativistic distorted wave model. © 2006 The American Physical Society.Articl

Sensitivity of quasielastic (p,n) spin-transfer observables to relativistic Dirac effects

Spin-transfer observables have been calculated for the quasielastic (p,n) reaction according to the relativistic plane wave impulse approximation, using two different parametrizations of the NN interaction. The target nucleus is Ca40 and the proton lab energies range from 135 to 500 MeV, while the momentum transfer is kept fixed at a (fairly large) value of 1.97 fm-1. An analysis is made of the sensitivity of these spin observables with respect to relativistic Dirac effects, the form of the N vertex and exchange contributions to the NN amplitudes. These sensitivities are found to be selective with respect to the different spin observables over the whole proton energy range. The results are also compared to those of the corresponding (p,p) reaction, which we formerly presented. © 1995 The American Physical Society.Articl

Validity of the relativistic impulse approximation for elastic proton-nucleus scattering at energies lower than 200 MeV

We present the first study to examine the validity of the relativistic impulse approximation (RIA) for describing elastic proton-nucleus scattering at incident laboratory kinetic energies lower than 200MeV. For simplicity we choose a Pb208 target, which is a spin-saturated spherical nucleus for which reliable nuclear structure models exist. Microscopic scalar and vector optical potentials are generated by folding invariant scalar and vector scattering nucleon-nucleon (NN) amplitudes, based on our recently developed relativistic meson-exchange model, with Lorentz scalar and vector densities resulting from the accurately calibrated PK1 relativistic mean field model of nuclear structure. It is seen that phenomenological Pauli blocking (PB) effects and density-dependent corrections to σN and ωN meson-nucleon coupling constants modify the RIA microscopic scalar and vector optical potentials so as to provide a consistent and quantitative description of all elastic scattering observables, namely, total reaction cross sections, differential cross sections, analyzing powers and spin rotation functions. In particular, the effect of PB becomes more significant at energies lower than 200MeV, whereas phenomenological density-dependent corrections to the NN interaction also play an increasingly important role at energies lower than 100 MeV. © 2008 The American Physical Society.Articl

Quenching of the analyzing power for inclusive quasielastic (p→,p') scattering

Within the context of a nonrelativistic semiclassical distorted wave (SCDW) model, we demonstrate that the experimentally observed reduction of the inclusive quasielastic Pb208(p→,p') analyzing power relative to the value for free NN scattering, at incident laboratory kinetic energies of 290 and 200 MeV and at the centroid of the quasielastic peak, is mainly attributed to nuclear medium modifications of the NN effective interaction and also nuclear distortion effects on the scattering wave functions. In addition, the SCDW model also provides a satisfactory quantitative description of the unpolarized double differential cross section. © 2007 The American Physical Society.Articl

Pairing correlations and resonant states in the relativistic mean field theory

We present a simple scheme for taking into account the resonant continuum coupling in the relativistic mean field-BCS calculations. In this scheme, applied before in nonrelativistic calculations, the effect of the resonant continuum on pairing correlations is introduced through the scattering wave functions located in the region of the resonant states. These states are found by solving the relativistic mean field equations with scattering-type boundary conditions for the continuum spectrum. The calculations are done for the neutron-rich Zr isotopes. It is shown that the sudden increase of the neutron radii close to the neutron drip line, the so-called giant halo, is determined by a few resonant states close to the continuum threshold.Articl

Relativistic predictions of quasielastic proton-nucleus spin observables based on a complete Lorentz invariant representation of the NN scattering matrix

Within the framework of the relativistic plane wave impulse approximation (RPWIA), complete sets of quasielastic (p→,p→′) and (p→,n→) spin observables are calculated employing a general and complete Lorentz invariant representation of the NN scattering matrix (referred to as the IA2 representation). The use of a complete representation eliminates the arbitrariness of a previously used five-term parametrization (commonly called the IA1 representation) and allows for the correct incorporation of effective-mass-type medium effects within the RPWIA framework and within the context of the Walecka model. For quasielastic scattering from a 40Ca target at incident proton energies between 200 and 500 MeV, we investigate the sensitivity of complete sets of spin observables to effective nucleon masses for both IA1 and IA2 representations. In general it is seen that the IA1 representation may overestimate the importance of nuclear medium effects, whereas the IA2-based predictions nearly correspond to values for free nucleon-nucleon scattering.Articl

Neutron skin deduced from antiprotonic atom data

The relationship between the nucleon density at large radii and the value of the rms radius is investigated in the framework of Skyrme Hartree-Fock and relativistic mean-field models. From a comparison to the charge density we constrain the models in terms of the nuclear matter incompressibility and effective mass properties required to reproduce the density shape. The results are used to extract the rms neutron radius for Pb208 from antiprotonic atom data. The result for the difference between the neutron and proton rms radii, the so-called neutron-skin thickness, is S=0.20(±0.04)(±0.05) fm, where ±0.04 fm is experimental error from the antiprotonic line width, and ±0.05 fm is the theoretical error suggested from the comparison of the models with the experimental charge density. © 2007 The American Physical Society.Articl

Relativistic description of inclusive quasielastic proton-nucleus scattering with relativistic distorted-wave impulse approximation and random-phase approximation

We present a fully relativistic model for polarized inclusive quasielastic proton-nucleus scattering that includes relativistic distorted waves for the projectile and ejectile (RDWIA), as well as the relativistic random-phase approximation (RPA) applied to the target nucleus. Using a standard relativistic impulse approximation treatment of quasielastic scattering and a two-body Scalar, Pseudoscalar, Vector, Axial vector, Tensor (SPVAT) form of the current operator, it is shown how the behavior of the projectile/ejectile and target can be decoupled. Distortion effects are included via a full partial-wave expansion of the relativistic wave functions. Target correlations are included via the relativistic RPA applied to mean-field theory in quantum hadrodynamics. A number of novel analytical and numerical techniques are employed to aid in this highly nontrivial calculation. A baseline plane-wave calculation is performed for the reaction Ca40(p,p′) at an energy of 500 MeV and an angle θc.m.=40°. Here it is found that the effect of isoscalar correlations is a quenching of the cross section that is expected to become more pronounced at lower energies or for higher-density targets. A RDWIA calculation shows additional reduction and if isoscalar target correlations are included this effect is enhanced. © 2011 American Physical Society.Articl