Proton-proton Femtoscopy as a Probe of Short-range Structure in High-Energy O+O Collisions

Abstract

Short-range nucleon-nucleon correlations are a defining feature of the nuclear many-body wave function, yet they are invisible in the one-body density and therefore inaccessible to observables that measure a nuclear size. We show that proton-proton femtoscopy supplies the missing sub-femtometer sensitivity. In ${}^{16}$O+${}^{16}$O collisions at $\sqrt{{\mathrm{s}}_{\mathrm{NN}}}=$ 200 GeV, we compare three nuclear-structure inputs spanning mean-field, low-resolution cluster, and short-range-correlated descriptions. The $p$-$p$ correlation function separates all three, most sharply in peripheral collisions, where the \textit{ab initio} input suppresses the extracted source radius by $\sim 5\%$ relative to the mean-field baseline. Under identical conditions $\ddot{I}{€}^{+}$-$\ddot{I}{€}^{+}$ correlations respond an order of magnitude more weakly, and the $C_{pp}/C_{\ddot{I}{€}^{+}\ddot{I}{€}^{+}}$ double ratio retains the full effect, pointing to the short-distance weighting of the ${}^1{S}_0$ pair rather than to an overall rescaling of the source. The signal survives the leading theoretical systematic, the choice of strong-interaction potential, which we quantify explicitly. These results identify $p$-$p$ femtoscopy as a short-distance-resolved probe of light-nucleus structure, complementary to flow observables that constrain only the low-order moments of the initial geometry.

8 Pages 2 Figures; Comments are welcome