Relativistic predictions of exclusive 208Pb(p →,2p)207Tl analyzing powers at an incident energy of 202 MeV

Hillhouse G.C. ; Mano J. ; Cowley A.A. ; Neveling R. (2003)


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 3s1/2, 2d3/2, and 2d5/2 states in 208Pb, 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 σ-nucleon and ω-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 of 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.

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