Exploring the Strong Interaction of Three-Body Systems at the LHC

Deuterons are atomic nuclei composed of a neutron and a proton held together by the strong interaction. Unbound ensembles composed of a deuteron and a third nucleon have been investigated in the past using scattering experiments, and they constitute a fundamental reference in nuclear physics to constrain nuclear interactions and the properties of nuclei. In this work, $K^{+}\text{−}d$ and $p\text{−}d$ femtoscopic correlations measured by the ALICE Collaboration in proton-proton ($pp$) collisions at $\sqrt{s}=13\mathrm{TeV}$ at the Large Hadron Collider (LHC) are presented. It is demonstrated that correlations in momentum space between deuterons and kaons or protons allow us to study three-hadron systems at distances comparable with the proton radius. The analysis of the $K^{+}\text{−}d$ correlation shows that the relative distances at which deuterons and protons or kaons are produced are around 2 fm. The analysis of the $p\text{−}d$ correlation shows that only a full three-body calculation that accounts for the internal structure of the deuteron can explain the data. In particular, the sensitivity of the observable to the short-range part of the interaction is demonstrated. These results indicate that correlations involving light nuclei in $pp$ collisions at the LHC will also provide access to any three-body system in the strange and charm sectors.