We study the nuclear (or A) dependence of the coherent η photoproduction reaction in a relativistic impulse approximation approach. We use a standard relativistic parametrization of the elementary amplitude, based on a set of four Lorentz-and gauge-invariant amplitudes, to calculate the coherent production cross section from 4He, 12C, and 40Ca. In contrast to nonrelativistic treatments, our approach maintains the full relativistic structure of the process. The nuclear structure affects the process through the ground-state tensor density. This density is sensitive to relativistic effects and depends on A in a different manner than the vector density used in nonrelativistic approaches. This peculiar dependence results in 4He having a cross section significantly smaller than that of 12C - in contrast to existent nonrelativistic calculations. Distortion effects are incorporated through an η-nucleus optical potential that is computed in a simple "tp" approximation.
|Number of pages||4|
|Journal||Physical Review C - Nuclear Physics|
|Publication status||Published - Apr 1998|
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Nuclear and High Energy Physics