  The polarization degrees of freedom in photoinduced two-nucleon knockout from
finite nuclei are studied. It is pointed out that they open good perspectives
to study the dynamics of dinucleons in the medium in detail. The ($\gamma,pp$)
and ($\gamma,pn$) angular cross sections, photon asymmetries and outgoing
nucleon polarizations are calculated for the target nuclei $^{16}$O and
$^{12}$C and photonenergies ranging from 100 up to 500 MeV. It is investigated
to which degree the two-nucleon emission reaction is dominated by
photoabsorption on $^3S_1(T=0)$ proton-neutron and $^1S_0(T=1)$ proton-proton
pairs in the nuclear medium. The calculations demonstrate that dominance of $S$
wave photoabsorption in the ($\gamma,pn$) channel does not necessarily imply
that the reaction mechanism is similar to what is observed in deuteron
photodisintegration.

Nuclear Theory