Relativistic predictions of exclusive208Pb(p→,2p)

Abstract

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 • , −54.6 • ) -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 Schrödinger 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 σ-, ρ-and ω-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.

Relativistic predictions of spin observables for exclusive proton knockout reactions

“…The formalism for the relativistic distorted wave model has been presented in Refs. [2,4,5,6,7]. In this paper we briefly allude to the most important aspects of the model and refer the interested reader to the latter references for more detail.…”

“…The corresponding nonrelativistic prediction, indicated by the dashed line in Fig. (1), completely fails to describe the data despite exhaustive corrections including different kinematic prescriptions for the NN amplitudes, non-local corrections to the scattering wave functions, and density-dependent modifications to the free NN scattering amplitudes [1,2]. On the other hand, both Dirac and Schrödinger-equation-based models provide an excellent description of the unpolarized energy-sharing cross section, thus highlighting the application of spin observables, such as the analyzing power, for discriminating between different dynamical effects in nuclear systems.…”

Sensitivity of exclusive proton knockout spin observables to different Lorentz invariant representations of theNNinteraction

“…(III)] and, in particular, study the sensitivity of exclusive ( p, 2 p ) polarization transfer observables to these representations. In a previous paper we demonstrated the importance of including distorting optical potentials on the incident and outgoing scattering wave functions for a correct description of ( p, 2p) analyzing powers [2]. However, in order to simplify the present analysis, we consider a relativistic plane wave model, whereby all distorting optical potentials are set equal to zero in the Dirac equation.…”

“…Recently, we demonstrated that a model based on the relativistic distorted wave impulse approximation (DWIA) provides an almost perfect description of exclusive ( p, 2p) analyzing power data, whereas corresponding nonrelativistic Schrödinger-equation-based predictions completely fail [1,2,3]. For both dynamical models, however, the comparison of theoretical predictions to unpolarized cross section data yields similar spectroscopic factors which are also in good agreement with those extracted from (e, e ′ p) studies.…”

“…(2), we display in Fig. (3) the expansion coefficients α 1 (solid line), α 2 (dashed line), α 3 (dash-dotted line), and α 4 (dotted line), of the φ LJ,M J =− 1 K ) [top panel] and φ LJ,Mz=+ 1 K) [bottom panel] for proton knockout from the 3s 1/2 state in 208 Pb at 202 MeV, in terms of free Dirac plane waves [see Eq.…”