- th / 9 90 50 17 v 1 6 M ay 1 99 9 Relativistic Calculations of Induced Polarization in 12 C ( e , e ′ ~ p ) Reactions ∗

Relativistic calculations of the induced proton polarization in quasifree electron scattering on 12 C are presented. Good agreement with the experimental data of Woo et al. is obtained. The relativistic calculations yield a somewhat better description of the data than the non-relativistic ones. Differences between the two approaches are more pronounced at larger missing momenta suggesting further experimental work in this region. 1 A measurement of induced proton polarization in the 12 C (e, e ′ p) reaction has been reported recently by Woo et al. [1]. The data explore the low missing momentum region from 0 to 250 MeV/c in constant q-ω kinematics. The data were compared to non-relativistic DWIA calculations using the effective momentum approximation. Momentum distributions used in these calculations were obtained by fitting the 12 C (e, e ′ p) data of van der Steenhoven et al. [2]. The final state interactions of the outgoing proton were included using non-relativistic optical potentials. Two such potentials were compared, one obtained by a reduction of the relativistic potentials of Cooper et al. [3], and the other based on an empirical effective interaction (EEI). Both models provide reasonable agreement with the data, with a slight preference for the EEI model when a proton is removed from the 1p 3/2 shell. The results from both non-relativistic models pass through the lowest missing momentum point for the knockout of a 1p 3/2 proton. The change in polarization with increasing missing momentum is reproduced, but the calculations tend to fall below the data at higher missing momenta. The calculations predict that the polarization should rapidly become negative as the missing momentum is increased beyond 220 MeV/c. For the set of data attributed to knockout of a 1s 1/2 proton, the non-relativistic calculations follow the trend of the data for small missing mo-menta, but become large and negative for missing momenta beyond 150 MeV/c. The data, on the other hand, seem to indicate a polarization becoming positive at these larger values of missing momenta. There also exist relativistic calculations for the same reaction, which have primarily considered the cross section, or equivalently, the single–particle momentum distribution. These calculations have mainly been reported by Udias et al. [4, 5], Jin and Onley [6] and Hedayatipoor et al. [7]. Relativistic calculations of proton polarization for the reaction 16 O (e, e ′ p), have been reported previously by Johansson and Sherif [8]. In the present …