S.O. Sørensen

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 .

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.

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.

An experimental study of large-angle elastic scattering of charged mesons and antiprotons on protons at 20 and 30 GeV/c incident momenta

A description is given of an experiment to study elastic scattering of π±, K±and p on protons at c.m. scattering angles from 45° to 100° at incident laboratory momenta 20 GeV/c and 30 GeV/c. The corresponding t range is from −6.2 (GeV/c)2 to −28 (GeV/c)2. There are no previous observations for these reactions in this t range. High intensity and large geometrical acceptance were required in order to measure the low cross sections. The experiment used a double-arm spectrometer. MWPCs were used for reconstruction, and threshold and differential Cerenkov counters for identification. Scintillation counters, Cerenkov counters and a hadron calorimeter were used in the trigger. The trigger logic utilized specially designed matrices and a hard wired microprocessor. The π−p elastic scattering cross sections follow approximately the dimensional counting rule from 3.5 GeV/c.and up to 30 GeV/c. The cross sections decrease by seven orders of magnitude in this energy range. The data is compared to quark models. None of these models give a comprehensive description of the results. However, some modifications to these models improve their consistency with the data.

Large-angle elastic scattering of charged pions on protons at 20 and 30 GeV/c incident momenta

Abstract Elastic cross-section measurements are presented for π ± −p at 20 GeV/ c and π − −p at 30 GeV/ c incident momenta in the large angle region (50° to 90° in the c.m. system). The data are compared with published lower energy elastic cross sections. A test is made of the dimensional counting rules for π ± −p elastic scattering and some indication of a deviation from this rule is observed in the π − −p case. A comparison is also made with the predictions of the constituent interchange model. Although the broad features of the predictions are confirmed, there are some important discrepancies. Finally, the predictions of the model due to Preparata and Soffer are also compared with the new data.

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.

p-3 He reaction cross section at 200 MeV/c

Abstract Inelastic p - 3 He events at 192.8 MeV/ c are detected with a self-shunted streamer chamber. The measured reaction cross section is 392±23.8mb. This result is briefly discussed and compared with other reaction cross sections for low-energy p with light nuclei.

anti-p He-3 REACTION CROSS-SECTION AT 200-MeV/c

Abstract Inelastic p - 3 He events at 192.8 MeV/ c are detected with a self-shunted streamer chamber. The measured reaction cross section is 392±23.8mb. This result is briefly discussed and compared with other reaction cross sections for low-energy p with light nuclei.