MPIs are the tool to obtain information on the correlations between partons in
the hadron structure. In the case of pp collisions the effects of correlations in
the transverse coordinates and in fractional momenta are in fact unavoidably
mixed in the final observables. On the contrary, the contribution to the pA
cross section, where the projectile interacts with large momentum exchange
with at least two target nucleons simultaneously, has only a weak dependence
on the correlations in the transverse coordinates. By studying the simplest
case, double parton interactions in pD collisions, one can thus obtain non trivial
information on the two-body parton correlations.
