International Conference on Exotic Atoms and Related Topics - EXA2017

World data for elastic $\Lambda-p$ scattering over a wide range of relative momenta are quite scarce and only available for small beam momenta with an overall statistics of less then 200. The situation for $\pi^-$-induced reactions is even more limited. In order to improve the theoretical description, new constraints are necessary to parametrise the cross sections. In this context a dedicated $\pi^-$ + A (A = C, W) experimental campaign was performed at $p_\pi = 1.7$ $GeV/c$ with the HADES detector (SIS18/GSI). The $\Lambda$ yield has been studied and further on the $\Lambda - p$ correlation is investigated. For the reconstruction of the $\Lambda$ in the inclusive spectra the charged decay channel ($\Lambda \rightarrow p \pi^-$, BR = 63.9\%) is examined. After topological cuts, an integrated yield of ~11k $\Lambda$ has been extracted with a purity of 93\% ($\pi^- + W$). The data is corrected for limited efficiency and acceptance and extrapolated to uncovered phase space by using a Boltzmann distribution. For the study of the $\Lambda - p$ correlation it is necessary to know all kinematic variables of the $\Lambda$ before the scattering, which are reconstructed with the incoming beam and the outgoing $K^0$. Thus, events with a matching charge pattern ($\Lambda \rightarrow \pi^- p, K^0 \rightarrow \pi^+ \pi^-, p$) are selected. Based on a likelihood-method the particle species is determined considering the specific energy-loss in the MDCs and velocity $\beta$. Since the selected pattern contains two $\pi^-$ and p in the final state, an event hypothesis is applied to assign their corresponding mother particle. The best combination is selected by a simultaneous matching of the invariant mass to the nominal value within the detector resolution. This procedure leads to an extraction of $\sim$6k events in the $\pi^- + W$ system. \newline Shown on the poster is the extracted $\Lambda$ yield, aside with the preliminary $\Lambda - p$ correlation. * supported by the DFG cluster of excellence "Origin and Structure of the Universe" and BMBF 05P15WOFCA