C. Maher

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

The production of antihyperon‐hyperon pairs out of the antiproton‐proton collison has been studied by the PS185 collaboration using the Low Energy Antiproton Ring (LEAR) at CERN. The emphasis of the studies is to investigate the production threshold region. Results obtained for the reactions pp→ΛΛ and pp→ΛΣ°=c.c. are presented and discussed. Total‐ and differential cross sections were measured, polarizations, spin correlations and singlet fractions were extracted at a variety of incident antiproton momenta.The investigations of the collaboration concentrated on the ΛΛ‐final channel. Data on pp→ΛΛ are a vailable for a rather wide energy range. A few results on the ΛΣ channel were analyzed as well as some events for the pp→Σ+Σ+ reaction. Further investigations on the charged sigma final hyperon‐antihyperon pairs are planned and in progress.

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

Results from the experiment PS 185 investigating the production of antilambda (Λ) lambda (Λ) and K° K° out of the antiproton (p) proton (p) annihilation are reported. In particular, the threshold measurements of the reaction pp→ΛΛ is discussed. From the shapes of the excitation function and of the angular distribution higher angular momentum contributions are conclued even at enegies close to to threshold. An interconnection of ΛΛ and the K° K channels to the ξ(2230) resonance is search for.