Proton-induced deuteron knockout reaction as a probe of an isoscalar proton-neutron pair in nuclei

Background: The isoscalar $pn$ pair is expected to emerge in nuclei having the similar proton and neutron numbers but there is no clear experimental evidence for it.Purpose: We aim to clarify the correspondence between the $pn$ pairing strength in many-body calculation and the triple differential cross section (TDX) of proton-induced deuteron knockout ($p,pd$) reaction on $^{16}\mathrm{O}$.Methods: The radial wave function of the isoscalar $pn$ pair with respect to the center of $^{16}\mathrm{O}$ is calculated with the energy density functional (EDF) approach and is implemented in the distorted wave impulse approximation framework. The $pn$ pairing strength ${V}_{0}$ in the EDF calculation is varied and the corresponding change in the TDX is investigated.Results: A clear ${V}_{0}$ dependence of the TDX is found for the $^{16}\mathrm{O}(p,pd)^{14}\mathrm{N}({1}_{2}^{+}$) at 101.3 MeV. The nuclear distortion is found to make the ${V}_{0}$ dependence stronger.Conclusions: Because of the clear ${V}_{0}$-TDX correspondence, the ($p,pd$) reaction will be a promising probe for the isoscalar $pn$ pair in nuclei. For quantitative discussion, further modification of the description of the reaction process will be necessary.