First measurement of the strange particles $R_{CP}$ nuclear modification factors in heavy-ion collisions at the SPS

The NA57 experiment has measured the $p_{T}$ distributions of $K_{s}^{0}$, $\Lambda$, and $\bar{\Lambda}$ particles in fixed-target Pb-Pb interactions at $\sqrt{s_{NN}}$=17.3 GeV as a function of the collision centrality. In this paper we study the central-to-peripheral nuclear modification factors and compare them to other measurements and to theoretical predictions.