Nijmegen preprint HEN-372 January 1995

. Backward proton production is studied in interactions of ß + and K + mesons with Al and Au nuclei at 250 GeV/c. The proton momentum spectra are measured at different emission angles. From the two-proton correlations, it is found, that a significant part ((26\Sigma4)% for Al and (44\Sigma6)% for Au) of the backward proton production can be attributed to secondary pion absorption by a nucleon pair in the nuclear medium, ß + (pn) ! /\Gamma p p and ß 0 (pp) ! /\Gamma p p. It is found that the share of the secondary pion absorption can be fitted by a power dependence / A fi , with fi = 0:27 \Sigma 0:05. An upper limit of the cross section for the colour-charge-exchange mechanism of backward proton production is estimated. 1 EC guest scientist, now at DESY, Hamburg 2 Onderzoeksleider NFWO, Belgium 3 Supported by the Polish State Committee for Scientific Research 4 Now at UIA, Wilrijk, Belgium 1 Introduction Backward proton production (BPP ) is kinematically forbidd..