Strange baryon and in particular multi-strange baryon production is suggested to be a useful probe in the search for quark gluon plasma formation in heavy ion collisions. We have measured the (Ω − + Ω + ) (Ξ − + Ξ + ) production ratio to be 0.8±0.4 at central rapidity and ϱ T > 1.6 GeV/c.
Strange and multistrange baryon production is expected to be enhanced in heavy ion interactions if a phase transition from hadronic matter to a Quark-Gluon Plasma takes place. The production yields of Λ s, Λ s, Ξ − s, and Ξ + s relative to the production of negative particles are presented for sulphur-tungsten interactions at 200 GeV/ c per nucleon. These production yields are compared to those produced in proton-tungsten interactions and the enhancements of strange and multistrange baryons and antibaryons are presented.
We find an increase in ∑ ± production between E cm = 4 and 7 GeV which is consistent with charmed baryon production models. A search for the decay ∧ c − → ∑ ± π ± π − yields no significant peaks.
We report on a high precision measurement of ϕ-meson production in continuum events and in direct decays of the Υ(1S)- and Υ(2S)-mesons. The ratio of the total production rate of ϕ-mesons in direct Υ(1S)- and Υ(2S)-decays over that in continuum events is 1.32±0.08±0.09 and 1.07±0.13±0.11 respectively. This is compatible with the corresponding ratio obtained for lighter mesons, but is appreciably smaller than the relative baryon production rate.
We report on measurements of the inclusive production rate of Sigma+ and Sigma0 baryons in hadronic Z decays collected with the L3 detector at LEP. The Sigma+ baryons are detected through the decay Sigma+ -> p pi0, while the Sigma0 baryons are detected via the decay mode Sigma0 -> Lambda gamma. The average numbers of Sigma+ and Sigma0 per hadronic Z decay are measured to be: < N_Sigma+ > + < N_Sigma+~ > = 0.114 +/- 0.011 (stat) +/- 0.009 (syst), < N_Sigma0 > + < N_Sigma0~ > = 0.095 +/- 0.015 (stat) +/- 0.013 (syst). These rates are found to be higher than the predictions from Monte Carlo hadronization models and analytical parameterizations of strange baryon production.
The production of charmed particles by Sigma- of 340 Gev/c momentum was studied in the hyperon beam experiment WA89 at the CERN-SPS, using the Omega-spectrometer. In two data-taking periods in 1993 and 1994 an integrated luminosity of 1600 microb^-1 on copper and carbon targets was recorded. From the reconstruction of 930 +- 90 charm particle decays in 10 decay channels production cross sections for D, antiD, Ds and Lambdac were determined in the region xF>0. Assuming an A^1 dependence of the cross section on the nucleon number, we calculate a total ccbar production cross section of sigma(x_F > 0) = 5.3+- 0.4(stat)+-1.0(syst)+1.0(Xi_c) microb per nucleon. The last term is an upper limit on the unknown contribution from charmed-strange baryon production.
Production of Sigma- and Lambda(1520) in hadronic Z decays has been measured using the DELPHI detector at LEP. The Sigma- is directly reconstructed as a charged track in the DELPHI microvertex detector and is identified by its Sigma -> n pi decay leading to a kink between the Sigma- and pi-track. The reconstruction of the Lambda(1520) resonance relies strongly on the particle identification capabilities of the barrel Ring Imaging Cherenkov detector and on the ionisation loss measurement of the TPC. Inclusive production spectra are measured for both particles. The production rates are measured to be <N_{Sigma-}/N_{Z}^{had}> = 0.081 +/- 0.002 +/- 0.010, <N_{Lambda(1520)}/N_{Z}^{had}> = 0.029 +/- 0.005 +/- 0.005. The production rate of the Lambda(1520) suggests that a large fraction of the stable baryons descend from orbitally excited baryonic states. It is shown that the baryon production rates in Z decays follow a universal phenomenological law related to isospin, strangeness and mass of the particles.
The production of antineutrons and charged Σ's in e+e− annihilations has been measured at s=4 and 7 GeV and at the ψ(3.1) resonance. Two packages containing spark chambers, steel plates, and scintillation counters were added to each side of the Mark I detector at SPEAR. Antineutrons were identified by annihilations which produced large-angle charged prongs characteristic of a high-Q reaction. The resulting antineutron cross sections and momentum distributions are consistent with previous antiproton results. Charged Σ's were detected by forming mass combinations with the n's and charged tracks in the Mark I. A clear signal is seen in the 7-GeV and ψ data, with little or no signal at s=4 GeV. The increase in Σ± production between 4 and 7 GeV is consistent with simple expectations for charmed-baryon production. A search for the decays Λc−→Σ±π∓π− and Σc*Σc→Λc−π± yields no significant peaks. An upper limit, at the 90% confidence level, of σΛcB(Λc→Σ±π∓π−)<56 pb is set.