Exploring the N\ensuremath{\Lambda}\textendash{}N\ensuremath{\Sigma} coupled system with high precision correlation techniques at the LHC

The interaction of and hyperons (Y) with nucleons (N) is strongly influenced by the coupled-channel dynamics. Due to the small mass difference of the N and N systems, the sizable coupling strength of the N ↔ N processes constitutes a crucial element in the determination of the N interaction. In this letter we present the most precise measurements on the interaction of p pairs, from zero relative momentum up to the opening of the N channel. The correlation function in the relative momentum space for p ⊕ p pairs measured in high-multiplicity triggered pp collisions at √s = 13 TeV at the LHC is reported. The opening of the inelastic N channels is visible in the extracted correlation function as a cusp-like structure occurring at relative momentum k∗ = 289 MeV/c. This represents the first direct experimental observation of the N ↔ N coupled channel in the p system. The correlation function is compared with recent chiral effective field theory calculations, based on different strengths of the N ↔ N transition potential. A weaker coupling, as possibly supported by the present measurement, would require a more repulsive three-body NN interaction for a proper description of the in-medium properties, which has implications on the nuclear equation of state and for the presence of hyperons inside neutron stars.