J. Seydoux

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.

Study of the reaction anti-p p ---> anti-Lambda Lambda at 1.546-GeV/c 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

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.

\bar{p} p \to \bar{\ell}

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.

ambda

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 .

\lambda

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.

at {LEAR}

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.

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

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.

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

Abstract The reaction p p → Y Y is being investigated at LEAR in the energy range from threshold up to 2.0 GeV/c. Integrated and differential cross sections as well as polarizations have been measured at six energies for the Λ Λ channel. At 1.546 GeV/c also spin correlations have been determined. The results are discussed and compared with different theoretical predictions. First and preliminary results on the reaction p p → K S K S in the energy range of the hypothetical ξ (2232) resonance are presented. The cross section is flat, and shows no indication of a structure.