Hyperon polarisation in the reaction (p)over-bar12C -> (Lambda)over-bar Lambda X

Data from the (p) over bar(12)C --> <(Lambda)over bar>Lambda X reaction, co llected by the PS185 experiment at antiproton momenta around 1.44 GeV/c, 1. 66 GeV/c and 1.77 GeV/c, have been analyzed and the Lambda and <(Lambda)ove r bar> polarisations have been extracted. The events are classified as quasi-free or non-quasi-free and it is found t hat the polarisations for Lambda and <(Lambda)over bar> differ in the latte r case. Such an effect comes from differences in the interaction of the out going Lambda and <(Lambda)over bar> with the residual nucleus and the measu rement constitutes the first information on <(Lambda)over bar> interaction with nuclear matter.