Inclusive phi-meson production in neutral current deep inelastic e+p scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 45 pb^{-1}. The phi mesons were studied in the range 10<Q2<100 GeV2, where Q2 is the virtuality of the exchanged photon, and in restricted kinematic regions in the transverse momentum, p_T, pseudorapidity, eta, and the scaled momentum in the Breit frame, x_p. Monte Carlo models with the strangeness-suppression factor as determined by analyses of e+e- annihilation events overestimate the cross sections. A smaller value of the strangeness-suppression factor reduces the predicted cross sections, but fails to reproduce the shapes of the measured differential cross sections. High-momentum phi mesons in the current region of the Breit frame give the first direct evidence for the strange sea in the proton at low x.
The production cross sections for the Λ, Σ0, Ξ−, Σ0 (1385), Ξ0 (1530) and Ω− hyperons have been measured, both in the continuum and in direct ϒ decays. Baryon rates in direct ϒ decays are enhanced by a factor of 2.5 or more compared to the continuum. Such a large baryon enhancement cannot be explained by standard fragmentation models. The strangeness suppression for baryons and mesons turns out to be the same. A strong suppression of spin 3/2 states is observed.
The production of Δ ++ baryons has been measured using 3.5 million hadronic Z 0 decays collected with the OPAL detector at LEP. The production rate and fragmentation function are presented. A total of 0.22 ± 0.04 ± 0.04 Δ ++ + ( Δ ) −− per hadronic Z 0 decay is observed. The fragmentation function is found to be softer than that predicted by the JETSET and HERWIG Monte Carlo event generators. With this measurement of Δ ++ production, at least one baryon of each strangeness level in the lightest baryon decuplet has now been measured at LEP.
The production of neutral strange hadrons is investigated using deep-inelastic scattering events measured with the H1 detector at HERA. The measurements are made in the phase space defined by the negative four-momentum transfer squared of the photon 2 < Q^2 < 100 GeV^2 and the inelasticity 0.1 < y < 0.6. The K_s and Lambda production cross sections and their ratios are determined. K_s production is compared to the production of charged particles in the same region of phase space. The Lambda - anti-Lambda asymmetry is also measured and found to be consistent with zero. Predictions of leading order Monte Carlo programs are compared to the data.
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.
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