O. Skjeggestad

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+.

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).

Experimental study of Ko → π+ π− πo decays and search for CP violation

The time distribution of 180 uniquely identified π+π−πo decays of the Ko meson between 0.04 and 20 KSo lifetimes has been studied. We find that the ratio η+−o of the KSo→π+π−πo to the KLo →π+π−πo amplitude is consistent with no CP violation. Our results confine η+−o to ∼0 < Reη+−o < −2 with small negative values of Imη+−o. If we set Reη−o = 0, we obtain Imη+−o = 0.37−-.34+0.47. If in addition we use the known value of Γ(KLo → π+π−πo) we obtain Imη = −0.23−0.25+0.31. Without these restrictions, a more accurate determination of η+−o can only be made, with the present statistics, by a combination of Ko and Ko data. Assuming η+−o = 0, we find Γ(KLo → π+π−πo = (2.35 ± 0.20) × 106 s−1.

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.

Experimental study of the selection rule ΔS = ΔQ in Koe3 and Koμ3 decays

We have studied the time distribution of semi-leptonic decays of the neutral K meson produced in a hydrogen bubble chamber in the reaction K+p → Kopπ+ with K+ momenta between 1.2 and 1.7 GeV/c. We have identified 306 πev decays and 74 πμv decays of known lepton charge with proper times between 0.04 and 20 KS lifetimes. The results are compatible with no violation of the ΔS = ΔQ rule. For the ratio x of the ΔS = −ΔQ amplitude to the ΔS = ΔQ amplitude we find the values +0.06+0.13inKe3decays:Re⁡xe=0.05inKμ3decays:Re⁡xμ=0.10−0.07−0.16+0.06+0.16Im⁡xe=0.08Im⁡xμ=−0.03−0.07,−0.18. Assuming ΔS = ΔQ we find the rate Γ(KoL → πev + πμv) = (12.4 ± 0.7) × 106 s−1.

Measurement of the KSO mean life

We have measured theKSO mean life using a sample of 50 000 KO → π+π− decays in a hydrogen bubble chamber. We obtain τ = (0.8958 ± 0.0045) × 10−10 s. This value is significantly higher than the present world average of τ = (0.862 ± 0.006) × 10−10 s.

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)%.

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).

Energy spectrum of charged pions from K− captures in CF3Br

Abstract From about 30 000 stopped K − mesons in the Ecole Polytechnique bubble chamber filled with CF 3 Br, a search has been made for long-range π − mesons due to the reaction K − + Br → → Λ Br + π − , in an attempt to determine a lower limit of the Λ binding energy in Λ Br. No event compatible with this reaction has been found. Results from measurements of the total π − and π + energy spectra have been used to investigate the production and trapping of Λ hyperons in K − captures on complex nuclei. From the frequency of Λ production associated with the emission of π − mesons with kinetic energy > 110 MeV, the fraction of directly produced Λ hyperons being trapped in the production nuclei was estimated as 0.29 −0.07 +0.15 . For Λ hyperons due to Σ conversion a lower limit for the same quantity is 0.28 ± 0.05.

Measurement of the

We have measured theKSO mean life using a sample of 50 000 KO → π+π− decays in a hydrogen bubble chamber. We obtain τ = (0.8958 ± 0.0045) × 10−10 s. This value is significantly higher than the present world average of τ = (0.862 ± 0.006) × 10−10 s.