Failure of the Coexistence Model to Account for Observed Two-Neutron Pickup Cross Sections

We have studied the ($p,t$) reaction on $^{18}\mathrm{O}$ and $^{42}\mathrm{Ca}$ at ${E}_{p}=41.7$ MeV. The observed yields to the ${0}^{+}$, $T=0$ states in $^{16}\mathrm{O}$ and $^{40}\mathrm{Ca}$ are at variance with distorted-wave Born-approximation predictions using the coexistence model to describe the initial and final states of the targets. By use of wave functions which employ a more extensive set of configurations, satisfactory agreement with the observed yields is achieved for the reaction $^{18}\mathrm{O}(p,t)^{16}\mathrm{O}$.