Single Diffraction Dissociation Research Articles

The “true” multiplicity distribution in K −p interactions and the two-component model

A method is presented for deriving channel cross sections for all multiplicities, considering both charged and neutral particles, for K −p reactions of pion production, Thus the “true”, rather than charged, multiplicity is obtained. The input data are the channel cross sections measured with four- and one-constraint fits. The model employed is the two-component one, so that for each reaction channel, separate cross sections are derived for kaon diffraction, proton diffraction and for non-diffractive processes. Results are obtained up to the highest energies at which data of channel cross sections are available, i.e. up to 16 GeV/ c incoming momentum, and some extrapolation is also made towards higher energies. It is found that the cross section for single kaon diffraction dissociation is equal to that for single proton diffraction dissociation. In the energy range considered, the sum of kaon and proton single diffraction processes has a cross section of (2.4 ± 0.3) mb, i.e., about 75% of the elastic cross section. The cross section for kaon diffraction dissociation into (Kπ) is consistent with zero.

Quantum number transfer in K −p interactions

Five-body final states from K −p interactions at 6, 10 and 16 GeV/ c are separated into sub-reactions depending upon which particles go forward in the c.m. system. The relative population and energy dependence of the various sub-reactions are shown to be closely related to the quantum numbers exchanged between the forward and backward going particles. In particular the energy dependence is the same as that found for the production of two-body final states involving exchange of the same quantum numbers. Single diffraction dissociation of the incident kaon and proton are shown to be important processes in these five-body states. We refer to this technique of separating events as binary LPS.

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

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.

Single and double dissociation in π−p collisions at 11 and 16 GeV/ c

The reactions π −p → 2 π − π +p, π −p → 2 π − π + π o p and π −p → 2 π −2 π +n are analysed at 11 and 16 GeV/ c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π −p → 2 π − π +p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π −p → (2 π − π +)p, and of the proton, π −p → π −( π − π +p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π −p → (2 π)( πp) decrease with increasing energy. In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/ c a maximum for single dissociation of the proton into 3 πp, namely π −p → π −( π − π + π o p); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π −p → π −( π −2 π +)n. Another strong maximum corresponds to the pion dissociation π −p → (2 π − π + π o )p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π −p → (2 π −2 π +)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π −p → (2 π − π +)( π o p) and π −p → (2 π − π +)( π +n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed. An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy.