  A systematic global investigation of pairing properties based on all
available experimental data on pairing indicators has been performed for the
first time in the framework of covariant density functional theory. It is based
on separable pairing interaction of Ref. [1]. The optimization of the scaling
factors of this interaction to experimental data clearly reveals its isospin
dependence in neutron subsystem. However, the situation is less certain in
proton subsystem since similar accuracy of the description of pairing
indicators can be achieved both with isospin-dependent and mass-dependent
scaling factors. The differences in the functional dependencies of scaling
factors lead to the uncertainties in the prediction of proton and neutron
pairing properties which are especially pronounced at high isospin and could
have a significant impact on some physical observables. For a given part of
nuclear chart the scaling factors for spherical nuclei are smaller than those
for deformed ones; this feature exists also in non-relativistic density
functional theories. Its origin is traced back to particle-vibration coupling
in odd-$A$ nuclei which is missing in all existing global studies of pairing.
Although the present investigation is based on the NL5(E) covariant energy
density functional (CEDF), its general conclusions are expected to be valid
also for other CEDFs built at the Hartree level.
