H. Tøfte

Structure in differential cross section distributions of two-body reactions in 8 GeV/c π+p interactions

Abstract From 60 000 two- and four-prong interactions of 8 GeV/c positive pions in hydrogen, total cross sections have been determined for elastic scattering, for 13 inelastic two-body reactions which represent about 7% of the total cross section, and for the various many-body channels. For elastic scattering and the other two-body reactions, the differential cross section dσ/dt′ is studied in detail, especially in the forward direction. It is found that (a) in the region near t′ = 0 a dip is observed in the channels N ∗++ η, N ∗++ ω and p ϱ , and possibly also in N ∗++ π o and N∗++A2o; however, the forward dips predicted by the Regge-pole conspiracy model with factorisation for the channels N ∗++ ϱ o and N ∗++ f o are not observed, on the contrary N ∗++ ϱ o presents a steep rise near t′ = 0; (b) at larger t′ values, a dip is observed for the pϱ+ channel at about 0.55 GeV2 and for the N∗++A2o channel at about 0.45 GeV2; (c) in general, the dσ/dt′ distributions can be fitted in the small |t′| region by the function exp (−At′), while over a larger t′ range, a fit of the form exp (−at′ + bt′2) is more satisfactory. However, for the channels N ∗++ ϱ o and N∗++fo a significantly better fit is obtained between 0 and 2 GeV2 with the sum of two exponentials, K1 exp (−Ct′) + K2 exp (−Dt′), with the break point at |t′| = 0.2 GeV2; C is about 15 GeV−2, while D is about 3 GeV−2. The latter is about the same value as obtained for elastic scattering in the t′ range from 0.7 to 2.0 GeV2.

Mass dependence of the small angle differential cross section for high energy interactions

Abstract A study of differential cross sections for 8 GeV/ c π + p and 10 GeV/ c K − p reactions, treated as two-body processes, has indicated that as the mass M of one of the “bodies” varies, the small angle differential cross section is described by d σ /d t ′ = K exp (− At ′) for all values of M , whether corresponding to a resonance or to a “background” region. In general, similar values of A are obtained for a resonance region and for its neighbouring mass bands. In most channels, as M increases, the angular distribution becomes broader, namely, A ∝ M − α , with 0 α

Strange particle production in 8 GeV/c positive pion interactions in hydrogen

Abstract Results are presented on strange particle production in 8 GeV/c π+p interactions with three and four particles in the final state. Total cross sections for different channels and for production of different resonances are estimated. Differential cross sections for quasi two-body reactions are given. Evidence is presented for the production of a (ΛK) enhancement with a mass of 1755 ± 21 MeV and a full width of 220 ± 60 MeV. Branching ratios for rare decay modes of A1, A2, fo and f′ into strange particles are given. In the ( K K π ) mass distribution possible enhancements are observed at 1490 and 1690 MeV.

The g-meson

The present status of our knowledge of the properties of the g-meson is summarized and discussed. New results obtained by the ABC collaboration in a 8 GeV/c π+p experiment, concerning (2π)+ and (4π)+ enhancements at about 1700 MeV, are presented. For the question of the g-meson spin, it is shown that the two types of determinations based on analyses of the decay angular distributions published in the literature, as well as the analysis attempted on these 8 GeV/c results, all favouring JP = 3−, cannot be considered as definitive. A third method of spin analysis is here tried, based on a study of the g-meson cross section as a function of the g-meson spin and elasticity, using the OPE model. This new method is a general one which could be applied to other resonances with production mechanism similar to that of the g-meson. It is found that in the framework of this model, (a) irrespective of the spin assignment, the g-meson must have elasticity η < 1, which means that the g → 2π and at least part of the 4π enhancement are the same object, (b) assuming that all the 4π enhancement derives from the g-meson, the experimental value of the elasticity η ≈ 0.4, favours JP = 3−.

Comparison of π±p and K−p reactions with a multiperipheral model using the Van Hove hexagon and cuboctahedron plots

Abstract Several reactions of 8 ifGeV/ cπ + p , 10 GeV/ c K − p and 16 GeV/ c π − p have been compared with the multiperipheral Regge-pole model of chan, Łoskiewicz and Allison, using the technique of longitudinal phase-space plots introduced by Van Hove, to investigate the relative importance of the various exchange diagrams. While the gross features of the data are satisfactorily reproduced at all

Experimental evidence from π+p reactions at 8 GeVc against the hypothesis of pion regge conspiracy plus factorisation

Abstract It has been predicted that with the hypothesis of a Regge trajectory conspiring with the pion trajectory and applying the factorisation theorem, the differential cross section for the reaction π + p → N ∗ ϱ 0 should have a dip in the forward direction near t = 0. It is shown that no such dip is observed in 8 GeV c π+p interactions.

A study of the reaction K−p → pKoπ− with the Veneziano model

Abstract The five-point function Veneziano model has been applied to the reaction K − p → p K 0 π − in the energy range from ≈ 3 to 10 GeV/c. The predictions of the model are shown to be sensitive to the choices made for the assumptions and the parameters involved in the expression of the amplitude. Several choices can be made that give a satisfactory general description of this reaction. However, the mass spectra are not described in detail and the differential cross sections do not have the correct t-dependence, especially at the lower energies. These difficulties derive mostly from the fact that the simple model used does not consider the possibility that more than one trajectory is exchanged between a pair of particles.

Ξ−, Ω− and antibaryon production in 10 GeV/c K−p interactions

Production of Ξ−, Ω− and antibaryons has been studied in 10 GeV/c K−p interactions. The Ξ∗(1530) is produced in about 15% of the reactions with Ξ− production. Four unambiguous examples of Ω− production with decay into (ΛK) have been observed: this gives a lower limit for the Ω− production cross section of 2.5 μb. One example of anti-Xi has been found. Distributions and average values of transverse and c.m. longitudinal momenta are presented.

Quark-model predictions for joint decay distributions in π+p double resonance production reactions at 8 GeV/c

Abstract The quark-model predictions of Bialas and Zalewski are compared with the experimental results for the joint decay distributions in the double resonance production reactions π + p → N ∗++ ϱ 0 , π + p → N ∗++ ω at 8 GeV /c . The relations fall into three categories, which differ in the assumptions made. Those of class A, which depend only on the additivity assumption, are found to be well satisfied for both reactions, within large errors. Similar agreement is found for relations of class B. A number of class C relations are badly violated in Jackson and helicity frames but are found to be valid in the Donohue-Hogaasen system.

Production of proton-antiproton and kaon-antikaon pairs in four-body reactions of 8 GeV/c π+ and 10 GeV/c K− on protons

The production of (pp), (K+K−) and (π+π−) pairs in four-body reactions of 8 GeV/c π+ and 10 GeV/c K− on protons has been studied. The cross sections for these processes are smaller in K−p interactions than in π+p interactions. For both π+ and K− induced reactions, the production of a K+K− pair is about 30 times less probable than that of a π+π− pair. In K−p interactions frequent production of φ but not of fo is observed, whereas in π+p interactions fo production is observed but not φ production. The production of the N∗(3755) isobar decaying into (ppp), reported by other authors, is not confirmed. The results are discussed in terms of a simple additive quark model.