The interaction due to the residual strong force between nucleons and antikaons is a fundamental element used in chiral effective theories where kaons are active degrees of freedom. The attractive or repulsive nature of the interaction is very sensitive to the relative distance between the two particles. Different experimental approaches explored the low-energy antikaon-proton interaction such as scattering experiments or with exotic atoms. The former cannot reach momenta below a few hundreds of MeV/c and the latter are limited to distances typical to the energy levels of the negative kaon substituting the electron in the hydrogen or helium atom. 

In Pb-Pb collisions, the average distance between particles is proportional to the cube root of the average charged particle multiplicity. The average distances for semi-central lead collisions are 4 fm and they reach 10 fm in the central ones. The strong interaction has been measured using the two-particle correlations at low relative momentum in six distance intervals. The ChiEFT calculations capture the main features of the antikaon-proton correlation function for the 6 analysed centrality intervals.

Further reading

ALICE Collaboration 2021