Relativistic plane wave predictions of polarization transfer observables for ($\vec{p},2\vec{p}\,$) knockout reactions from the 3s$_{1/2}$ state in $^{208}$Pb at 392 MeV

TL;DR

This study evaluates the relativistic plane wave impulse approximation (RPWIA) for describing polarization transfer and cross sections in proton knockout reactions from lead-208, comparing it to the more complete RDWIA model.

Contribution

It demonstrates that RPWIA can quantitatively predict polarization transfer observables and qualitatively describe cross sections within certain energy ranges for specific nuclear reactions.

Findings

RPWIA agrees with RDWIA for polarization transfer observables.

RPWIA qualitatively reproduces the shape of the cross section.

Sensitivity to RMF models affects the cross section predictions.

Abstract

Exclusive ($\vec{p},2\vec{p}$) reactions are often described within the Relativistic Distorted Wave Impulse Approximation (RDWIA) model to include nuclear distortion effects. The Relativistic Plane Wave Impulse Approximation (RPWIA) model, on the other hand, neglects these effects on the incident and outgoing proton wave functions. Our aim is to identify kinematic regions where the RPWIA model quantitatively describes energy-sharing analyzing power (A$_y$) and qualitatively describes the unpolarized triple differential cross section ($\sigma$) data. Where no data exist, we also seek regions where RPWIA gives similar results of the complete set of polarization transfer observables (D$_{i'j}$) compared to RDWIA. The sensitivity of the RPWIA predictions to different Relativistic Mean Field (RMF) models will be assessed. For an incident 392 MeV proton beam and coplanar scattering angles, $\theta_{a'} = 32.5^\circ$ and $\theta_{b'} = -50.0^\circ$, the RPWIA predictions of $\sigma$ and A$_y$ are compared to published data for ($\vec{p},2\vec{p}$) knockout from the 3s$_{1/2}$ state in $^{208}$Pb. In the RPWIA model the proton wave functions are treated as Dirac plane waves, the $NN$ interaction is modeled using the relativistic IA1 parameterization of the Relativistic Impulse Approximation (RIA) framework, and the boundstate wave functions are extracted from the RMF models. We found that within a range of $\pm10$ MeV around the peak of $\sigma$, the RPWIA and RDWIA models quantitatively describe the A$_y$ data and qualitatively the $\sigma$. Here, the RPWIA and RDWIA predictions agree for D$_{i'j}$. While $\sigma$ is sensitive to the RMF models, D$_{i'j}$ is not. Thus concluding that RPWIA can be applied to quantitative description of D$_{i'j}$ in a limited range for proton knockout from the 3s$_{1/2}$ state in $^{208}$Pb, and qualitatively describe the shape of $\sigma$.