Shedding Light on (Anti-)nuclei Production with Pion-Nucleus Femtoscopy

Abstract

High-energy nuclear collisions provide a unique environment for synthesizing both nuclei and antinuclei (such as $\bar{d}$ and $\overline{^4\text{He}}$) at temperatures ($k_BT\sim100$ MeV) nearly two orders of magnitude above their binding energies of a few MeV. The underlying production mechanism, whether through statistical hadronization, nucleon coalescence, or dynamical regeneration and disintegration, remains unsettled. Here we address this question using a novel tool of pion-nucleus femtoscopy. By solving relativistic kinetic equations for pion-catalyzed reactions ($\pi NN \leftrightarrow \pi d$) for deuteron production and including a $70~\mathrm{MeV}/c^2$ downward shift of the in-medium $\Delta(1232)$ mass, we successfully reproduce the resonance peaks observed by the ALICE Collaboration in both $\pi^+-p$ and $\pi^+-d$ femtoscopic correlation functions in high-multiplicity $pp$ collisions at $\sqrt{s} = 13~\mathrm{TeV}$. We further find that the nucleon coalescence model reproduces only about half of the observed peak strength, while the statistical hadronization model predicts no resonance feature. These results provide compelling evidence that pion-catalyzed reactions play a dominant role in the production of light (anti-)nuclei in high-energy nuclear collisions and cosmic rays.