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.