Multiparticle Final States Research Articles

Direct-simulation Monte Carlo models for high-energy inelastic processes

Three Monte Carlo models are presented for providing descriptions of center-of-mass angular distributions, longitudinal and transverse momentum distributions, and effective-mass distributions for multiparticle final states produced in high-energy inelastic processes. They are applied specifically to the reaction pp → ppπ+π−, and the results are compared with experimental data for this reaction at incident-proton laboratory momenta of 22 GeV/c and 10 GeV/c. One of the models I involves a virtual dissociation of the target (projectile) into pπ+π− with projectile (target) involved only to the extent that its longitudinal momentum is reduced sufficiently to permit the target (projectile) associated pπ+π− to be freed in the final state with overall energy-momentum conservation. A second model II has the target (projectile) dissociating into pπ+ and the projectile (target) dissociating into pπ−. Both I and II include additional exchanged systems to provide transverse-momentum transfer from the target to projectile system. The last model III is based on a virtual dissociation of both target and projectile into a proton and another system (mass taken as zero). These two systems combine and decay into π+ and π−. It is shown that a particular combination of I and III provides a good qualitative description of the ppπ+π− data at both 10 GeV/c and 22 GeV/c.

Analysis of some multiparticle final states produced in K −-proton interactions at 6 GeV/ c

The reactions K − p→ p K o π +π −π −, p K o π +π −π − π o and n K o π +π +π −π − have been studied at 6 GeV/ c incident momentum. Cross sections are given for the various resonances produced in each channel. In the first two channels, resonance production dominates. A detailed analysis has been performed on the simultaneous resonance production K − p→ Δ ++ K ∗−π − , and evidence is given for a vector-ex-change mechanism. A Veneziano-model calculation has been attempted for this quasi three-body final state, and the predictions are found to be in good agreement with the experimental results.

Models for High-Energy Processes

Recent developments in the concepts and models used to describe high-energy collisions of fundamental particles are reviewed. The areas of appreciable activity in research in high-energy physics are surveyed briefly and the general framework for the description of processes at high energies is outlined. There follows a sampling of recent experimental data designed to show the extent and detail of present-day experimental results. Recent applications of Regge pole models are reviewed with emphasis on the difficulties as well as the successes of models employing only Regge poles. The various multiple-scattering models are then discussed and correlated by means of the methods of Glauber. The connection of these models with amplitudes having branch cuts in the angular-momentum plane (Regge cuts) is described, as well as some comparisons with experiment. Finite energy sum rules as a means of relating the low-energy and high-energy domains are discussed in some detail. Next, the far-reaching concept of duality whereby the direct-channel resonances are (in some sense) the crossed-channel Regge exchanges is described, along with the related ideas of exchange degeneracy, the special role of the Pomeranchon Regge pole, and duality diagrams. An explicit realization of duality is achieved in the Veneziano model. This model is discussed in some detail for the relatively simple and interesting example of pion-pion scattering. Brief mention is also made of the extensions of the Veneziano model to the $n$-particle amplitude, attempts at unitarization, and various applications. The topic of multiparticle final states is covered relatively briefly with emphasis on the applications of double Regge pole exchange to three-body final states, the calculation of proton and pion energy and angular distributions in proton-proton collisions by means of the multi-Regge exchange model, and the generation of self-consistent Regge singularities with the multi-Regge exchange model and unitarity. The final section of the review concerns recent results on pion-pion scattering phase shifts and also $K\ensuremath{-}\ensuremath{\pi}$ phase shifts, and some remarks on theorems connecting decay correlations of resonances with the mechanism of production. The literature survey ended, with a few exceptions, in May 1969.

Strange-Particle Production inπ+−pCollisions

Strange particles produced in interactions of positive pions with protons have been studied with the Brookhaven 20-in. bubble chamber, which was exposed to ${\ensuremath{\pi}}^{+}$ beams of 2.35, 2.62, and 2.90 BeV/c. Cross sections are presented and the production of resonances is discussed. The outstanding feature of the multi-particle final states is that they are dominated by $K\ensuremath{-}\ensuremath{\pi}$, $K\ensuremath{-}\overline{K}$, and $Y\ensuremath{-}\ensuremath{\pi}$ resonances. The isotopic spin of the $\ensuremath{\phi}$ is confirmed to be zero and no evidence is found for a $\ensuremath{\phi}$ decay into three pions.

Remarks on the phenomenological analysis of resonances

Some remarks are made concerning various aspects of the analysis of resonances produced in multi-particle final states resulting from high-energy collisions. The shape and position of a resonance are discussed by means of the connection between production cross-sections for stable and unstable particles, and a numerical example ofN* as seen in KN → KN* at different energies is given. The relation between the present description of the resonant effects and others (Watson’s finalstate interaction formula and the one-meson-exchange model of Chew and Low) is examined. Off-the-mass-shell corrections to the one-meson-exchange model are obtained in a relatively simple way. The bearing of the decay angular correlations on the production mechanism is explored ; co-ordinate axes appropriate for the peripheral model are specified; the equivalence of the azimuthal angular distribution and the Treiman-Yang distribution is established. Angular correlations are given for the decay of boson resonances (J=l, 2) resulting from definite spin and parity states in thet-channel. Some remarks are made about the inclusion of nonresonant contributions when there is a mixture of pseudoscalar and vector exchange.