In the Standard Model, b quarks produced in e^+e^- annihilation at the Z^0 peak have a large average longitudinal polarization of -0.94. Some fraction of this polarization is expected to be transferred to b-flavored baryons during hadronization. The average longitudinal polarization of weakly decaying b baryons, <P_L^{\Lambda_b}>, is measured in approximately 4.3 million hadronic Z^0 decays collected with the OPAL detector between 1990 and 1995 at LEP. Those b baryons that decay semileptonically and produce a \Lambda baryon are identified through the correlation of the baryon number of the \Lambda and the electric charge of the lepton. In this semileptonic decay, the ratio of the neutrino energy to the lepton energy is a sensitive polarization observable. The neutrino energy is estimated using missing energy measurements. From a fit to the distribution of this ratio, the value <P_L^{\Lambda_b}> = -0.56^{+0.20}_{-0.13} +/- 0.09 is obtained, where the first error is statistical and the second systematic.
Charge conjugate states are included.
Data on multiplicity, correlations, and inclusive spectra of KS0 mesons and Λ0(Λ¯0) hyperons produced with xF≤0 in inelastic pNe20 and pN interactions at 300 GeV are presented and compared. The inclusive cross sections for pNe20 (pN) with xF≤0 are 61.1±2.8 mb (3.34±0.64 mb) for KS0, 40.8±2.5 mb (1.89±0.29 mb) for Λ0, and 3.9±0.5 mb (0.31±0.08 mb) for Λ¯0. The multiplicity ratio for pNe20 and pN interactions is 1.58±0.16 for KS0, 1.95±0.23 for Λ0, and 1.12±0.43 for Λ¯0. We have observed the Σ0(1193) hyperon and measured the average multiplicity (nΣ0=0.049±0.027) for xF≤0. We have also observed the strange resonances K*(892), K*(1415), and Σ*(1385) with xF≤0 and measured the fraction of V0 coming from each resonance. Λ0 polarization for xF≤0 is measured and shows a decrease as p⊥ increases [pΛ(pNe20)≈−0.25 at p⊥=1.5 GeV/c], in agreement with other experiments which measure polarization in the region xF≫0. Since (43±7)% of the Λ0 are produced in Σ0→Λ0γ decays, the Λ0 polarization is significantly greater than the measured values. Experimental results are compared to predictions of the Lund model and the dual parton model of soft hadron-nucleus and hadron-nucleon interactions.
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Axis error includes +- 0.0/0.0 contribution (NOT GIVEN).
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Results are presented on the inclusive photoproduction of λ and λ for incident photon energies between 25 and 70 GeV. The slope parameter of the p T 2 distribution is found to be 2.83±0.1 GeV −2 for λ and 3.28±0.25 GeV −2 for λ . The x F distributions, measured in the range −0.2 to 0.7, show that while λ are produced centrally, λ production extends to more negative values of x F ; the shapes show no energy dependence and are similar to those in pion-induced reactions. The polarization of the produced λ is less than 10%. The results are discussed in terms of vector dominance and quark fusion models.
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The polarization parameter for K + n charge exchange scattering has been measured at five momenta between 0.851 GeV/ c and 1.351 GeV/ c for centre of mass angles −0.8 < cos θ ∗ < 0.8 . Results from a phase shift analysis incorporating these results are presented. No Z ∗ resonances are observed.
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The polarizaton parameter has been measured for K + n elastic scatteringat five incident beam momenta between 0.851 GeV/ c and 1.351 GeV/ c for c.m. angles in the range −0.9 < cos θ ∗ < 0.9 . It is in good agreement with the most recent partial wave analysis of the KN system.
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The polarization parameter has been measured for K − p elastic scattering at nine incident beam momenta between 0.955 and 1.272 GeV/ c covering the c.m. angular range −0.9 < cos θ ∗ < + 0.9 . Experimental results and coefficients of Legendre polynomial fits to the data are presented and compared with other measurements and a partial-wave analysis.
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LEGENDRE POLYNOMIAL COEFFICIENTS FOR POLARIZATION DERIVED USING INTERPOLATED DIFFERENTIAL CROSS SECTION DATA OF B. CONFORTO ET AL., NP B105, 189 (1976).
New results on inclusive lambda polarization in K − p interactions at 14.3 GeV/ c are presented. At the kaon fragmentation vertex, the polarization is compared to that from inclusive experiments at lower momenta and to that from two-body reactions with a Λ. As predicted by the triple-Regge model with N α (or N γ ) exchange, the polarization is found to be independent of s and M X 2 / s . In particular it has the same value as that found in the two-body reactions.
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AVERAGED OVER ALL PRODUCTION ANGLES.
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