Exploring two-particle correlations in p+Nb reactions

The HADES collaboration measured in 2008 the collision of a proton with a niobium nucleus ( p + Nb), where the kinetic energy of the proton was Ekin = 3.5 GeV. This pA system offers the possibility to study two-particle correlations in an interesting environment, namely in a small system at rather low energies which means low multiplicity. On the one hand side we can compare the results with trends established in heavy-ion collisions at much larger energies to see similarities or find differences and their ex planations and on the other hand the measurements are free from correlation-disturbing effects like mini-jets which are produced at LHC energies. The latter point is a good reason to investigate the interaction of particles where the inter action strength is not well established (e.g. between Λ hyperons and protons). It was found in [1] that the pΛ correlation function is sensitive to the size of the particle emission re gion because the strong interaction between both particles is large enough that they can interact in their final state. Two-particle correlations are experimentally determined by the ratio: