A1ρπ couplings andt-channel helicity conservation

Abstract

Recently experimental observations in hadron-hadron collisions have revealed new features in the high-energy production processes known as diffractive dissociation such as the production and the decay of particles like A 1 and Q mesons (1). The characteristic features of these events are an almost constant total cross-section and the conservat ion of the t-channel helicity inferred from the study of the density matrix of the pro. duced particle (A 1 or Q) in the Gottfried-Jackson frame. Another unusual property of these diffractively produced particles is that their spectrum cannot be fitted by a Breit. Wignertype amplitude and as such their interpretations as resonances are still dubious. At the present t ime there exists no quanti tat ive understanding of these processes as we have for resonance production processes, mediated by Regge exchanges, poles and/or cuts. A qualitative explanation in this regard has been put forward in the form of the selection rule proposed by MORRISON (2), CA~LITZ (S) and CHOW and YANG (4). There have been a few theoretical a t tempts to explain the peculiar features such as the helicity conservation and constant cross-section in terms of the pomeron (P), but these attempts are not very much decisive due to the uncertain nature of the pomeron itself. Recently the very existence of the pomeron in these reactions has been put to quest ion through an elegant analysis of the density matr ix elements in the Gottfried-Jaekson frame in a Veneziano model (which does not incorporate a pomeron) by ROBERTS (5). Further, it has been shown by FREUND et al. (e) that in a twisted-loop model for the pomeron, helicity conservation in the t-channel in = p ~ A i p demands that these conservations hold only if the P-f and p exchange contributions each separately conserve t-channel helicity. MUF, LLER (7) and AHMED et al. (s) obtained information about Alp= couplings by applying the idea of t-channel helicity conservation to ==-~=A~ and ~ A ~ = A ~ scattering, respectively. They have observed that the t-channel helici~y conservation