CERN Accelerating science

The first measurements of the scattering parameters of ΛK pairs in all three charge combinations (ΛK$^{+}$, ΛK$^{−}$, and ΛK$_{S}^{0}$) are presented. The measurements are achieved through a femtoscopic analysis of ΛK correlations in Pb-Pb collisions at $\sqrt{s}$NN = 2.76 TeV from ALICE at the LHC. The femtoscopic correlations result from strong final-state interactions, and are fit with a parametrization allowing for both the characterization of the pair emission source and the measurement of the scattering parameters for the particle pairs. Extensive studies with the THERMINATOR 2 event generator allow for the description of the non-femtoscopic background, resulting mainly from collective effects, with unprecedented precision. Furthermore, this model together with HIJING simulations are used to account for contributions from residual correlations induced by feed-down from resonances. In the experimental data, a striking difference is observed in pairs with low relative momenta ($k$$^{*}$ $\leq$ 100 MeV) between the ΛK$^{+}$ and ΛK$^{−}$ correlations, and the ΛK$_{S}^{0}$ system exhibits features between the two. The ΛK$^{+}$ system exhibits a negative real component of the scattering parameter($R$f0), while those of the ΛK$^{−}$ and ΛK$_{S}^{0}$ are positive, although the magnitude of that of the ΛK$_{S}^{0}$ is smaller than that of the ΛK$^{−}$. The results suggest an effect arising from different quark-antiquark interactions between the pairs ($s$$\bar{s}$ in ΛK$^{+}$ and $u$$\bar{u}$ in ΛK$^{−}$),or from different net strangeness for each system (S=0 for ΛK$^{+}$, and S=−2 for ΛK$^{−}$). To investigate further, we conduct a Ξ−K$^{±}$ analysis, for which preliminary results are shown. Finally, the ΛK systems exhibit source radii larger than expected from extra polation from identical particle femtoscopic studies. This effect is interpreted as resulting from the separation in space-time of the single-particle Λ and K source distributions.