A.G. Frodesen

The inclusive single-particle spectra of π−, KS0 and Λ in proton-proton collisions at 19 GeV/c

Abstract Data on the inclusive production spectra of K S 0 and Λ from proton-proton collisions at 19 GeV are presented and discussed in connection with the earlier studied inclusive π − production spectrum. The three single-particle spectra are compared with a crude two-center thermal model for the average radiation from the pp collisions.

The four-prong annihilation of 1.2 GeV/c antiprotons in hydrogen (II) π+π+π−π−π0 final state

Abstract Approximately 17 000 four-prong annihilations of 1.2 GeV/ c antiprotons in hydrogen have been analyzed. The present report considers those events with one neutral pion (5π). The 5π events show production of ϱ 0 , ϱ ± , f 0 , ω 0 , η 0 mesons, and the possibility of a ϱϱ enhancement at 1400 MeV/ c and/or a ϱπ enhancement at 1080 MeV/ c is considered. The influence of the Bose-Einstein correlation function of Goldhaber et al. [6] is investigated. Centre-of-mass angular distributions of the pions and centre-of-mass opening angles between pairs of pions are presented. The production upper limits at the 95% confidence level, for several resonant states are given.

The four-prong annihilation of 1.2 GeV/c antiprotons in hydrogen (I): Four-pion final state

Abstract Approximately 17 000 four-prong annihilations of 1.2 GeV/c antiprotons in hydrogen have been analyzed. The cross section for annihilation into four prongs is 31.6 ± 1.0 mb and the partial cross section for the 4π final state 2.9 ± 0.2 mb. The 4π state, which is reported here, shows production of ϱ0, f0, A2± mesons and an enhancement in the 3π and/or ϱπ system at the mass of the A1 meson. The frequencies of various resonance channels have been determined. Two-body intermediate states account for 40–60% of the 4π final state. Centre-of-mass angular distributions of the pions are presented. A change in the momentum dependence of the forward-backward asymmetry of the pions is observed at a pion momentum corresponding to the production of A2±π+.

Strange particle cross sections and multiplicity distributions in 19 GeV/c proton-proton interactions

Inclusive cross sections are presented for strange-particle production in proton-proton interactions at 19 GeV/c for the pairs (K0K0C=+1, K0Λ, K+Λ, K0Σ+, K0Σ− and for Λ, Ks0, Σ+, Σ− and Ξ−. The KK, the KY and the total strange particle cross sections have been found to be 1.40 ± 0.10 mb, 2.69 ± 0.09 mb and 4.23 ± 0.20 mb, respectively. The charged multiplicity distributions for events with Ks0, Λ, (K0K0)C=+1 or K0 Λ are shown to follow a modified KNO curve, whereas K+ Λ does not. For the inclusive reactions pp→(K0K0)C=+1 + X++, pp→K0Λ + X++ and pp → Λ + X++, we find that the average charged multiplicity of the remainder system X++ is the same as when X++ is produced in other reactions with the same system energy and quantum numbers.

A triple-Regge analysis of the inclusive reaction pp → Λ + X++ at 19 GeV/c

Abstract The inclusive reaction pp → Λ + X ++ at 19 GeV/ c beam momentum has been analyzed in terms of the triple-Regge formalism. A good description of the structure function is achieved for events with | t | c ) 2 . The effective trajectory obtained from fits to the M 2 / s distribution in different t bins is α R ( t ) = −(0.38 ± 0.11) + (1.15 ± 0.07) t , which holds up to a | t | value of 4 (GeV/ c ) 2 . This is consistent with the K trajectory rather than the K ∗ trajectory which has been reported from other experiments.

The four-prong annihilation of 1.2 GeV/c antiprotons in hydrogen (III) K+K−π+π− and K+K−π+π−π0 final states

Abstract From approximately 12 000 four-prong annihilations of 1.2 GeV/ c antiprotons in hydrogen about 200 events involving two charged kaons were selected mainly on basis of ionization. The cross sections for the K + K − π + π − and K + K − π + π − π 0 final states are 260 ± 40 μ b and 290 −60 +40 μ b, respectively. The amounts of resonances produced have been estimated. The four-body final state is dominated by K ∗ (890) production, whereas the five-body final state shows an abundant production of K ∗ (890), ω(783) and o(1019).

PREDICTIONS OF MULTI-REGGE MODELS FOR THE ANTIPROTON--PROTON ANNIHILATION TO FOUR CHARGED PIONS.

The predictions of the multi-Regge model of Chan. Łoskiewicz and Allison (CLA) and of two modified versions by Plahte and Roberts and by Roberts have been examined by comparison with observations for the annihilation channel p+p → 2π+ + 2π− at 1.2, 3.3 and 5.7 GeV/c incoming antiproton momentum. The CLA model is found to give a good description of various single-particle distributions, such as c.m. angles and longitudinal and transverse momenta. The Roberts model also provides a fair account of all single-particle distributions, whereas the Plahte-Roberts model is less successful. In its original form the CLA model does not incorporate resonance formation. The other models, on the other hand, seem to over emphasize two particle resonance production compared to the experimental findings. Attempts to remedy this discrepancy are discussed. The first model gives a correct variation of the cross section with the antiproton momentum, whereas the other models predict cross sections which seem to decrease too fast with the antiproton momentum.

Production of Λ-hyperons in K− interactions at rest in CF3Br

Abstract An investigation has been made of Λ-hyperons produced by about 39000 K − mesons stopping in the Ecole Polytechnique bubble chamber filled with CF 3 Br. Approximately 1600 Λ-hyperons decaying by the charged mode were measured. From a comparison of the momentum spectra of Λ-hypersons originating in various types of K − interactions, the percentage of Λ-hyperons produced in K − captures on more than one nucleon is estimated to lie between (22±4)% and (40±3)%. Observed momentum and angular distributions are compared with expectations for different reactions as calculated from an optical model. The amplitude for direct Λ-production in K − captures on pairs of protons is shown to be small, and it is likely that most Λ-hypersons from multi-nucleon K − captures are indirectly produced. The total emission rate of Λ-hyperons from K − interactions at rest in CF 3 Br is (60±3)%.

The spin and parity of the A2± produced in pp annihilations

Abstract Evidence supporting the assignment J P = 2 + for the A 2 meson is obtained from analysis of p p → ππππ with 1.2 GeV/ c antiprotons.

A systematic study of hypernuclei from Σ− captures in nuclear emulsions

Abstract A total of 35 hypernuclei produced by stopping Σ− hyperons in nuclear emulsions has been studied with main emphasis on the identification problem. A kinematical analysis of the hypernucleus production and decay stars has been combined with mass and charge determination of individual prongs. Out of 25 non-mesic hypernuclei, 8 could be uniquely identified and 4 assigned a unique charge. All 10 mesic decays could be uniquely identified. The emission rate of measurable hypernuclei from Σ− capture is found to be (3.7 ± 0.9)%. For hypernuclei of charge Z≧2 the overall non-mesic to mesic decay ratio is 4.2 ± 1.9).