  Excitation of pairing vibrations in superfluid nuclei is studied by using a
kinetic model based on the Vlasov equation with pairing, derived from the
time-dependent Hartree-Fock-Bogolyubov theory. The anomalous density response
function is used to find the monopole pairing mode and the dynamic variation of
the pairing gap associated with this mode. The spectroscopic factor for the
excitation of monopole pairing vibrations in two-neutron transfer reaction is
estimated. It is found that the pairing correlations give rise to the same
coherent contribution to the semiclassical spectroscopic factor as to the
corresponding quantum expression, which is essentially determined by the
distribution of the neutron levels near the Fermi energy. A numerical
evaluation of the reduced spectroscopic factor for the excitation of monopole
pairing vibrations in two-neutron transfer reaction in superfluid nuclei shows
that it does not exceed several percent of the spectroscopic factor for the
transfer of two neutrons to the ground state. This estimate is in agreement
with the experimental data obtained for the ratio of the cross section for the
excitation of 0+state in the (p,t) reaction in the energy region of double
pairing gap to the cross section for the excitation of the ground state for
superfluid nuclei of the rare-earth and actinide regions.
