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+−𝑑 and 𝑝−𝑑 femtoscopic correlations measured by the ALICE Collaboration in proton-proton (𝑝⁢𝑝) collisions at √𝑠=13  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+−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−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 𝑝⁢𝑝 collisions at the LHC will also provide access to any three-body system in the strange and charm sectors.