Within the relativistic plane-wave impulse approximation, the sensitivity of complete sets of quasielastic proton-nucleus spin observables is investigated with respect to relativistic effects, the importance of exchange contributions to the NN amplitudes, the form of the mN vertex, and spinorbit distortions. Calculations are performed at laboratory energies ranging from 135 to 500 MeV and for target nuclei ranging from C to Pb at a fairly large fixed momentum transfer of 1.97 fm . Of all the spin observables, only A"exhibits a clear relativistic efFect at the highest energy, as has been previously found. However, at the lower energies (200 MeV and below) the relativistic eRect shifts to two other polarization transfer observables, mainly D,t, and to a lesser extent D~t, . In addition, it is found that D"t"is extremely sensitive to the pseudoscalar versus pseudovector ambiguity of the xN vertex, whereas D,t~and D~tt are sensitive to exchange contributions to the NN amplitudes. Compared to the latter, the efFects of spin-orbit distortion are not insignificantly small and had to be corrected for. This investigation stresses the urgent need for measurements of the quasielastic spin observables at these low energies.PACS number(s): 24.10. Jv, 24.70.+s, 25.40.h

Based on the relativistic plane-wave impulse approximation for quasielastic ( p ជ ,p ជ Ј) and (p ជ ,n ជ ) polarization observables, we provide quantitative estimates of nuclear medium modifications of the NN interaction. We employ a 40 Ca target for proton energies ranging from 135 to 300 MeV at a momentum transfer of 1.97 fm Ϫ1 . Compared to former calculations, we have generated new meson-exchange parameters for the relativistic NN amplitudes between 80 and 200 MeV. Finally, the results are compared to the limited available data.

For the calculation of polarization transfer observables for quasielastic scattering of protons on nuclei, a formalism in the context of the Relativistic Plane Wave Impulse Approximation is developed, in which the interaction matrix is expanded in terms of a complete set of 44 independent invariant amplitudes. A boson-exchange model is used to predict the 39 amplitudes which were omitted in the formerly used five-term parameterization (the SP-VAT form) of the nucleon-nucleon scattering matrix. Use of the complete set of amplitudes eliminates the arbitrariness of the five-term representation. 24.10.Jv, 24.70.+s, Typeset using REVT E X where E 2 = p 2 + M 2 , and K n (n = 1 − 13) are kinematic covariants constructed from the Dirac matrices:K 9 = Q 22,µ (γ 5 ⊗ γ 5 γ µ ) K 10 = Q 12,µ (I 4 ⊗ γ µ )S K 11 = Q 21,µ (γ µ ⊗ I 4 )S K 12 = Q 12,µ (γ 5 ⊗ γ 5 γ µ )S K 13 = Q 21,µ (γ 5 γ µ ⊗ γ 5 )S

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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 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 parameterization (commonly called the IA1 representation) and allows for the correct incorporation of effective-mass-type medium effects within the RP-WIA framework and within the context of the Walecka model. For quasielastic scattering from a 40 Ca target at incident proton energies between 200 and 500 MeV, we investigate the sensitivity of complete sets of spin observablesto 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.