Systematics in the global polarization measurements of Λ hyperons with HADES at SIS18

Abstract

The global polarization of Λ hyperons has been measured in Au+Au and Ag+Ag collisions at √SNN = 2.4 and 2.55 GeV$\sqrt {{S_{{\rm{NN}}}}} = 2.4\,{\rm{and}}\,2.55\,{\rm{GeV}}$SNN=2.4 and 2.55 GeV recorded with HADES. An increase of the polarization is observed following the trend measured by the STAR Collaboration. The high statistics Ag+Ag data allowed for differential measurements of the polarization. The study of acceptance effects is very important in the fixed target setup, as the phase-space coverage is not symmetric. These studies are reported together with the evaluation procedure of the systematic uncertainties.