$\Lambda \mathrm{K}$ femtoscopy in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV

Abstract

The first measurements of the scattering parameters of $\Lambda$K pairs in all three charge combinations ($\Lambda$K${}^{+}$, $\Lambda$K${}^{-}$, and $\Lambda {\mathrm{K}}_{\mathrm{S}}^0$) are presented. The results are achieved through a femtoscopic analysis of $\Lambda$K correlations in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV recorded by 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 provide a good description of the non-femtoscopic background, which results mainly from collective effects, with unprecedented precision. Furthermore, together with HIJING simulations, this model is used to account for contributions from residual correlations induced by feed-down from particle decays. The extracted scattering parameters indicate that the strong force is repulsive in the $\Lambda {\mathrm{K}}^{+}$ interaction and attractive in the $\Lambda {\mathrm{K}}^{-}$ interaction. The data hint that the and $\Lambda {\mathrm{K}}_{\mathrm{S}}^0$ interaction is attractive, however the uncertainty of the result does not permit such a decisive conclusion. The results suggest an effect arising either from different quark-antiquark interactions between the pairs ($\mathrm{s}\overline{\mathrm{s}}$ in $\Lambda$K${}^{+}$ and $\mathrm{u}\overline{\mathrm{u}}$ in $\Lambda$K${}^{-}$) or from different net strangeness for each system (S = 0 for $\Lambda$K${}^{+}$, and S = $-2$ for $\Lambda$K${}^{-}$). Finally, the $\Lambda$K systems exhibit source radii larger than expected from extrapolation from identical particle femtoscopic studies. This effect is interpreted as resulting from the separation in space-time of the single-particle $\Lambda$ and K source distributions.

32 pages, 10 captioned figures, 5 tables, authors from page 23, published version, figures at http://alice-publications.web.cern.ch/node/6221

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• The $\Xi (1620)$ and $\Xi (1690)$ molecular states from $S=-2$ meson-baryon interaction up to next-to-leading order
• Femtoscopic study of the $\Lambda \alpha$ interaction
• Investigation of K${}^{+}$K${}^{-}$ interactions via femtoscopy in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV at the LHC
• Exploring the N$\Lambda$-N$\Sigma$ coupled system with high precision correlation techniques at the LHC