A two-step dynamical picture of diffraction dissociation and the high energy behaviour of transverse momenta

Abstract

It is known that single diffraction dissociation in few-body hadron collisions is sharply separated from non-diffractive processes even when the latter occupy neighbouring regions of phase space. A possible general explanation is that diffraction dissociation of a particle into successive channels of increasing multiplicity is characterized by a competition between these channels, a lower one being abruptly closed by the opening up of the next higher one. We show that this explanation works quite well for proton diffraction dissociation in π −p collisions at 16 GeV/ c. The reaction is considered as a two-step process, production of a fireball X( π −p→ π −X) and decay of X. By analysing the distributions in the mass of X, we find that the competition operates sharply between the decay channels X→ πN, 2 πN, 3 πN, and that it can be explained by pure phase space effect in the fireball decay. These results imply that the phase space effects just mentioned combined with the small momentum tranfer property of the dissociation π −p→ π −X are sufficient to account for the smallness of the transverse momenta p T of all second-aries in the reactions considered. We note that the situation would be different at much larger energies, where fireballs of very high mass could be occasionally produced. Irrespective of whether such heavy fireballs would be produced diffractively or not, phase space arguments now imply that their decay will tend to give both higher multiplicities and higher p T of the secondaries. We indicate the possible interest of these considerations for recent observations of large p T secondaries at the CERN Interesting Storage Rings.