Backward proton production in π⁺ andK ⁺ collisions with Al and Au nuclei at 250 GeV/c

Abstract

Backward proton production is studied in interactions of π⁺ andK ⁺ mesons withAl andAu 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±4)% forAl and (44±6)% forAu) of the backward proton production can be attributed to secondary pion absorption by a nucleon pair in the nuclear medium,$\pi ^ + (pn) \to \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\leftarrow}$}}{p} p$ and$\pi ^0 (pp) \to \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\leftarrow}$}}{p} p$. It is found that the share of the secondary pion absorption can be fitted by a power dependence αA ^β, with β=0.27±0.05. An upper limit of the cross section for the colour-charge-exchange mechanism of backward proton production is estimated.