Observation of t-channel helicity conservation in diffractive reactions producing A1 and Q-mesons

It is shown that helicity is conserved in the t-channel for A 1 and Q-meson production by pions of 8 and 16 GeV/ c and kaons of 10 GeV/ c , respectively. This is in contrast to evidence for s-channel helicity conservation reported for elastic scattering and rho photoproduction. This difference in behaviour of diffractive processes may be due to the fact that there is a change in spin in the former reactions but not in the latter, or, alternatively, to different mechanisms operating in the two cases.