The Experiment PS185 "Hyperon Production"

PS185 - PS185/2 - PS185/3

The experiment PS185 studies the exclusive production of strangeness in antiproton proton annihilations in flight at LEAR at CERN. Detailed information on the dynamics of strange-antistrange quark-pair creation has been obtained by precision measurements of total and differential cross sections, as well as final-state polarizations and spin correlations.
The experiment PS185/2 investigates Lambda-Antilambda pair production very close to the reaction threshold at 1435 MeV/c antiproton beam momentum. It will clarify an irregularity 1 MeV above the reaction threshold observed in the PS185 data.
The study of the dependence of the observables on the initial-state target-proton polarization is the objective of the experiment PS185/3. The experiment is currently setup in CERN's south-hall and is scheduled to take data from October to December 1996.
The reaction channels investigated from the respective thresholds up to the maximum antiproton beam-momentum of 2 GeV/c include neutral and charged hyperon-antihyperon pairs. The reaction channel into the KsKs final state has been investigated as well. Final states containing more then one photon cannot be distinguished. These are the Lambda-Antilambda-pi0 and the Sigma0-Antisigma0 channels, which have thresholds below 2 GeV/c.

Some results

Total cross sections

Differential total cross sections

Angular distributions of cross sections for the reaction p p-bar --> Lambda Lambda-bar have been measured at a variety of beam momenta between the reaction threshold at 1.435 GeV/c and the maximum available momentum at LEAR, which is 2 GeV/c. Presented here are data taken at 16.42 GeV/c antiproton momentum comprising about 43,430 events.

Polarizations

Polarizations for the reaction p p-bar --> Lambda Lambda-bar at 1642 MeV/c antiproton momentum.

Spin correlations

Here is also a compilation of results for the singlet fraction for the reaction p p-bar --> Lambda Lambda-bar

** Singlet Fraction ** 

 P(beam)   exc.E         MC           intrinsically
 [GeV/c]   [MeV]      corrected         corrected     references
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 1.489    18.932  -0.077 +/- 0.142                    PL B331 203  [FS91]
 1.546    39.056  -0.078 +/- 0.052                    NP A526 575  PL B199 147  [WD88]
 1.567    46.477  -0.113 +/- 0.089                    PL B331 203  [FS91]
 1.642    72.991                    -0.003 +/- 0.015  [HF92]
 1.6533   76.986  -0.055 +/- 0.040                    [RTo95]
 1.6583   78.753  -0.085 +/- 0.030                    [RTo95]
 1.695    91.725  -0.032 +/- 0.030                    NP A526 575  [GS89]
 1.726   102.677  -0.08  +/- 0.05                     [RTa95]
 1.7704  118.352  -0.024 +/- 0.037                    [RTo95]
 1.835   141.124                     0.014 +/- 0.030  [RK94]
 1.8918  161.103  -0.002 +/- 0.036                    [TS92]
 1.9034  165.178  -0.036 +/- 0.024                    [TS92]
 1.9185  170.479   0.010 +/- 0.016   0.058 +/- 0.016  [MZ92]
 1.9476  180.685   0.036 +/- 0.031   0.062 +/- 0.031  [RB95]
 1.9906  195.738  -0.026 +/- 0.031   0.031 +/- 0.031  [RB95]
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 average          -0.021 +/- 0.009  +0.028 +/- 0.009 
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CP violation

A=0.006+-0.015