LIMITS TO THE VALIDITY OF THE GLAUBER APPROXIMATION FOR HEAVY-ION SCATTERING, AND A POSSIBLE ASSESSMENT OF IN-MEDIUM NN PAULI BLOCKING

A feature universally employed in the application of the Glauber appro ximation to the scattering of a projectile by a many-particle target i s the assumption that the complex phase shift chi(b)/2 = delta(l) itse lf carries a phase which is independent of the impact parameter b. The most common assumption is that chi(b) = (alpha + i)g(b), where g(b) i s real and alpha = Re[f(0 degrees)]/Im[f(0 degrees)] is the real-to-im aginary ratio of the forward amplitude for elastic scattering of the p rojectile (or one of its constituents) on the constituents of the targ et. Since g(b) is proportional to an eikonal integral through an effec tive potential V + iW, this form also assumes that V(r) = alpha W(r), i.e., that the real and imaginary parts of this potential have the sam e radial shapes. In recent years this approximation has been applied t o heavy-ion elastic scattering in the relatively low-energy range belo w 100 MeV/nucleon. Phenomenological optical potentials for these same nuclei and energies strongly violate the above condition, although the y do approximate it in the Surface region responsible for scattering t o angles dominated by Fraunhofer oscillations. The Glauber approximati on provides a qualitative fit to these oscillations, indicating that i t is at least employing the correct nuclear radii. However, it grossly overestimates the absorption at larger angles in cases where these an gles are sensitive to the interior of the potential. This failure may provide a sensitive means of assessing the effects of Pauli blocking o n in-medium NN scattering.