Exploring the N$\Lambda$-N$\Sigma$ coupled system with high precision correlation techniques at the LHC

The ALICE collaboration
Phys.Lett.B 833 (2022) 137272, 2022.

Abstract (data abstract)
The interaction of $\Lambda$ and $\Sigma$ hyperons (Y) with nucleons (N) is strongly influenced by the coupled-channel dynamics. Due to the small mass difference of the N$\Lambda$ and N$\Sigma$ systems, the sizable coupling strength of the N$\Sigma\leftrightarrow$N$\Lambda$ processes constitutes a crucial element in the determination of the N$\Lambda$ interaction. In this letter we present the most precise measurements on the interaction of p$\Lambda$ pairs, from zero relative momentum up to the opening of the N$\Sigma$ channel. The correlation function in the relative momentum space for p$\Lambda\oplus\overline{\mathrm{p}}\overline{\Lambda}$ pairs measured in high-multiplicity triggered pp collisions at $\sqrt{s}=13~$TeV at the LHC is reported. The opening of the inelastic N$\Sigma$ 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$\Sigma\rightarrow$N$\Lambda$ coupled channel in the p$\Lambda$ system. The correlation function is compared with recent chiral effective field theory calculations, based on different strengths of the N$\Sigma\leftrightarrow$N$\Lambda$ transition potential. A weaker coupling, as possibly supported by the present measurement, would require a more repulsive three-body NN$\Lambda$ interaction for a proper description of the $\Lambda$ in-medium properties, which has implications on the nuclear equation of state and for the presence of hyperons inside neutron stars.

  • Table 1

    Data from Figure 1 (all panels)


    p-$\Lambda$ correlation function in high-multiplicity pp collisions at $\sqrt{s}=13$ TeV.

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