A. Haatuft

Neutral strange-particle production in p̄20Ne reactions at 607 MeV/c

Abstract The Λ 0 and K 0 s production cross sections have been measured at 607 MeV/ c for the reaction p + 20 Ne → V 0 + X ( V 0 =Λ, 0 , K 0 s ) . The Λ 0 /K 0 s production ratio is found to be (2.3±0.7). The data are consistent with an evaporative character of the emission mechanism from a multinucleon system for Λ 0 and from one nucleon for K 0 s . The rapidity distributions of negative tracks in K 0 x events are different from those in Λ 0 events without V 0 .

Antiproton-helium annihilation around 45 MeV/c

Abstract The p ¯ 4 He annihilation cross section averaged over the interval 40–50 MeV/c has been measured using a streamer chamber in a magnetic field. The measured value is 1342±250 mb. It agrees with a behaviour like 1/p of the annihilation cross section. Our result has been obtained at the lowest momentum achieved till now in measurements of antiproton annihilation in flight.

Strangeness production in antiproton annihilation at rest on 3He, 4He and 20Ne

Abstract New data are reported on antiproton annihilations at rest with production of Λ and K s 0 , using a streamer chamber with 3 He, 4 He and 20 Ne as gas targets. The data include Λ, K s 0 , ΛK s 0 and K s 0 K S 0 production rates and momentum distributions, π − momentum spectra, mean numbers of charged particles generally and of negatively charged particles separately for different reaction channels. The yields are compared to simple combinatorial calculations based on the extreme assumptions of Λ production via B = 1 or via B = 0 ( K rescattering) annihilations. Λ and K s 0 momentum spectra are compared to simple model calculations where B = 0 and B = 1 annihilations with and without final-state interactions are considered. A review of existing data on Λ and K s 0 production is presented, showing the dependence on the p momentum and on the mass number of the target.

Antiproton-neon annihilation at rest and at 607 MeV/c

Abstract The analysis is based upon pNe annihilation events at rest and at 607 MeV/c detected with a self-shunted streamer chamber exposed to the LEAR beams. The main measured quantities are the following: charged-prong multiplicity, negative pion multiplicity; momentum, angular and rapidity distributions. General distributions are given as well as distributions as functions of charged prong multiplicity. A correlation is found between high multiplicity and depth of the annihilation point. The data are compared with recent theoretical analyses.

Measurement of the branching ratios of multi-pion final states in pp annihilation at 1.6 GeV/c

Abstract The final results on the pionic annihilation of 1.6 GeV/ c antiprotons on free protons in the heavy liquid bubble chamber Gargamelle are presented here. Branching ratios of the various channels (including multi-π 0 channels) as well as multiplicity distributions for charged and neutral pions are given which are for the most part compatible with the prediction of the isospin statistical model.

Pionic annihilation of antiprotons stopped on 3He

Abstract The pionic annihilation of antiprotons stopped on 3 He nuclei in a self-shunted streamer chamber exposed to the antiproton beam of LEAR is studied. The data concern charged-particle multiplicity distributions, branching ratios for different final states, the probability of final-state interaction, π − , π + , p and d momentum spectra, like and unlike pion angular correlations, π and other charged-particle angular correlations. The comparison of the 3 He data with those obtained on 1 H, 2 H and 4 He does not reveal relevant effects due to the increase of the nucleon number; the small differences can be seen as due to a weak final-state interaction.

Annihilation of Antiprotons at Rest in 3He and 4He

Abstract At LEAR of CERN the annihilation of antiprotons, stopping in 3 He and 4 He filling a self-shunted streamer chamber in a magnetic field, has been studied. The charged-particle multiplicities have been measured and the relative probabilities of π − production in p 3 He and p 4 He annihilation events have been obtained. The ratio between the p annihilation probability on the neutron and the proton for 3 He and 4 He has been deduced to be about half the value obtained for 2 H in bubble chamber experiments. The analysis of the results shows that this difference cannot be due only to the pion final-state interaction or to the shadow effect of the nucleons of the nuclei. The probability of p annihilation at rest on a proton bound in the nucleus results to be twice as high as that on a bound neutron, showing the dominance of annihilation in the I = 0 isospin states.

Dilepton and trilepton production by neutrinos in Gargamelle at CERN SPS energies

Abstract We report on a search for ν μ N → μ − e − X and ν μ N → μ − e + e − X events in Gargamelle at CERN Super Proton Synchrotron (SPS) energies. Ten μ − e − events were found with p e − > 0.5 GeV/ c and p μ − > 4.5 GeV/ c (seven of these events have p e − > 0.8 GeV/ c ). The rate relative to the charged-current events is (6.7 ± 3.9) × 10 −4 , and to the opposite-sign dileptons 0.20 ± 0.11. Some characteristics of the μ − e − events are compared with μ − e + and charged-current events. Three ν μ N → μ − e + e − X events were observed with p e ± > 0.3 GeV/ c , p μ − > 4.5 GeV/ c , and m e + e − > m π 0 . The rate of these events relative to the charged-current events is (3.1 ± 1.9) × 10 −4 .

An experimental study of the production of neutral pions in p̄p annihilations at 1.6 GeV/c

Abstract The heavy liquid bubble chamber Garamelle has been used to study the rate of production of neutral pions in the pionic annihilation of 1.6 GeV/ c antiprotons on free protons. Preliminary results are presented on the relative cross-sections for most channels together with the mean π 0 multiplicity and the first moments for annihilation into 0-prongs, 2-prongs, 4-prongs and 6-prongs.

Evidence of isospin effects in antiproton-nucleus annihilation

Abstract Antiproton- 3 He annihilation events at rest have been detected using a self-shunted streamer chamber. The ratio of the cross section for annihilation on neutrons and on protons has been measured (0.467 ± 0.035). It is compared with other results from annihilation on free nucleons, deuterium, 3 He and 4 He. The low value of the ratio seems to indicate a strong isospin dependence of the antinucleon-nucleon P-wave amplitude.