Velocity distribution of secondary π mesons from 22.6-GeV/c proton--nucleus interactions in emulsion

Emulsion plates exposed to a 24-GeV proton beam are scanned. A velocity distribution of the secondary π mesons produced in such nuclear interactions is obtained. A Gaussian-type function is observed to simulate the experimental data and the usual phenomena of isotropy in the center-of-mass frame. Our results indicate that the assumption of the constant velocity for all the secondary particles is only an approximation to the real world.