Stellan Ohlsson

Study of the reaction pp→ΛΛ near threshold

Abstract Results are presented from a study of the reaction p p→ Λ Λ near threshold. Over 3000 events recorded at s values 14.6 and 25.5 MeV above the Λ Λ threshold (2231.2 MeV) have been analysed. Results for the production cross section, differential cross section, and the Λ and Λ polarization are given at both energies and are compared with recent theoretical calculations of this process.

Study of the reaction p̄p → \̄gLΛ at 1.546 and 1.695 GeV/c

Abstract The PS185 experiment at the CERN Low Energy Antiproton Ring (LEAR) has studied the reaction p p → gLΛ at several momenta. In this paper results from two runs with high statistics at 1.546 GeV/c and 1.695 GeV/c are described. Based on 4063 and 11362 analysed events, respectively, differential and integrated cross sections, polarizations and spin correlations are presented. The singlet fraction, extracted from the spin correlations, is consistent with zero at both momenta, showing that the gLΛ pairs are produced in a pure triplet state. A comparison of the decay asymmetry parameters of Λ and gL reduces the upper limits for the violation of the CP invariance for this system.

Threshold measurement of the reaction pp→ΛΛ at lear

Abstract The excitation function of the reaction p p→ Λ Λ in the threshold region has been measured at LEAR. Sixteen measurements of the total cross section, in the energy range between 0.85 MeV below threshold and 4.05 MeV above, are presented. The shapes of the measured differential cross sections indicate a remarkably strong p-wave contribution even down to the reaction threshold. We also report here the measurement of significant polarizations in the threshold region; these are compared with previous higher-energy data.

CP invariance in the reaction pp→ΛΛ→pπ+pπ− at 1.546 GeV/c

Abstract In a study of hyperon production with antiprotons at the CERN Low-Energy Antiproton Ring (LEAR), we have measured the ratio A=(α + α )/(α− α ) . Here α and α are the decay asymmetry parameters of the Λ and Λ non-leptonic charged decays. The hyperons were produced with identical polarization in the reaction p p→ Λ Λ at an incident p momentum of 1.546 GeV/c. The result, A=− 0.07 ± 0.09, is consistent with zero, as required from CP invariance.

Induced strategy shifts in spatial reasoning

Abstract Previous research on reasoning about spatial arrangements has revealed two major strategies used by adults: Series Formation and Elimination. It was hypothesized that all adults have both strategies available. An experiment was carried out in which subjects who showed no spontaneous tendency to shift strategy were induced to do so. The strategy shifts by the subjects are simulated by a computer program in the form of a homogeneous production system. The conditions under which homogeneous and hierarchical production system models will yield the same predictions are discussed.

Measurement of the reaction pp→ΛΣ0+c.c. at 1.695 GeV/c

Abstract The reaction p p → Λ Σ 0 together with its charge conjugate channel (c.c.) has been measured at LEAR. The incident p momentum was 1.695 GeV/c, corresponding to an excess energy above threshold of 14.8 MeV. Results are given for the production cross section and the differential cross section as well as for the polarization. Comparisons are made with theoretical calculations and with the reaction p p → Λ Λ .

Measurement of the reaction pp → KsKs in the region near s ≈2230 MeV

Abstract Measurements of the total and differential cross sections of the reaction p p → K s K s are presented for values of s in the region near 2230 MeV. The 18 energies of the scan were chosen to permit a sensitive search for resonant structure related to the ¢E(2230) state in a channel with a minimal non-resonant background. No such structure is observed. Stringent limits for the branching ratio are set based on various assumptions for the width and spin of the ¢E.

Study of the reaction pp → ΛΛ below 6 MeV excess energy

Abstract The reaction p p → Λ Λ → p π + pπ − is studied in the experiment PS185 at the CERN Low Energy Antiproton Ring (LEAR). A precise measurement of the excitation function in the immediate threshold region below 6 MeV excess energy was achieved. The total cross section shows an unexpected behaviour around 1 MeV excess energy.

The Enaction Theory of Thinking and Its Educational Implications

Abstract Ohlsson, S. 1983. The Enaction Theory of Thinking and Its Educational Implications. Scandinavian Journal of Educational Research 27, 73‐88. The educational objective of training pupils to think for themselves is widely accepted in contemporary education. The conception of thinking and knowledge which has been developed within Logic has influenced pedagogical thinking more than is commonly realized, due to the lack of precise alternatives. The new theory of thinking created by Allen Newell and Herbert A. Simon is summarized informally, and some of its educational implications developed. The theory implies that thinking is a skill, and thus should be taught like other skills, i.e. by teaching methods of how to perform it.

Study of the reaction\bar pp \to \bar \Lambda \Lambda close to threshold at LEARp→⊼Λ close to threshold at LEAR

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