  The nuclear mass dependence of the number of short-range correlated (SRC)
proton-proton (pp) and proton-neutron (pn) pairs in nuclei is a sensitive probe
of the dynamics of short-range pairs in the ground state of atomic nuclei. This
work presents an analysis of electroinduced single-proton and two-proton
knockout measurements off 12C, 27Al, 56Fe, and 208Pb in kinematics dominated by
scattering off SRC pairs. The nuclear mass dependence of the observed
A(e,e'pp)/12C(e,e'pp) cross-section ratios and the extracted number of pp- and
pn-SRC pairs are much softer than the mass dependence of the total number of
possible pairs. This is in agreement with a physical picture of SRC affecting
predominantly nucleon-nucleon pairs in a nodeless relative-S state of the
mean-field basis.
