The inclusive production of π± andK± mesons and of protons and antiprotons ine+e− annihilations has been measured at 34 GeV and 44 G
We present evidence for the production of Ξ· − , Ξ − in e + e − annihilation into hadrons. Our measurements yields: 0.026 ± 0.008 (stat.) ± 0.009 (syst.) Ξ − , Ξ − per hadronic event at W ∼ 34 GeV. Using our previous measurements of Λ, Λ and p, p production we obtain the relative yields (Ξ − , Ξ − /(Λ, Λ = 0.087 ± 0.03 ( stat. ) ± 0.03 ( syst. ) and (Ξ − , Ξ − /( p , p = 0.033 ± 0.011 ( stat. ) ± 0.011 ( syst. ) .
Production of the F meson by e + e − annihilation at high energies has been obsrved in the ϕπ final state with a mass of 1.975 ± 0.009 ± 0.010 GeV and a width consistent with the mass resolution. The yield of F production times branching ratio relative to μ pair production is R F ( x ⩾ 0.3) B (F ± → ϕπ ± ) = 0.061 ± 0.012 ± 0.018.
Measurements are presented of the inclusive cross section for K ∗ (892) ± production in hadronic decays of the Z 0 using a sample of about half a million events recorded with the OPAL experiment at LEP. Charged K ∗ mesons are reconstructed in the decay channel K 0 S π ± . A mean rate of 0.72±0.02±0.08 K ∗ mesons per hadronic event is found. Comparison of the results with predictions of the JETSET and HERWIG models shows that JETSET overestimates the K ∗± production cross section while HERWIG is consistent with the data.
The cross section for the processe+e−→π0+ anything has been measured at an average center of mass energy of 34.6 GeV for π0 energies between 0.7 and 17 GeV. The angular distribution for π0 energies larger than 2 GeV is of the formdσ/dΩ∼1+Acos2θ, withA=1.2±0.5. The ratio of π0 to π± production in the measured energy range is 2σ(π0)/(σ(π+)+σ(π−))=1.13±0.18
The production rates of the $J_{P}={1⩈er 2}^{+}$ octet Σ baryons in hadronic Z0 decays have been measured using the OPAL detector at LEP. The inclusive production rates per hadronic Z0 decay of the three isospin states (including the respective antiparticle) have been separately measured for the first time: $άtrix {n_{Sigma^{+}}=0.099pm 0.008pm 0.013ŗ n_{Sigma^{0}}=0.071pm 0.012pm 0.013ŗ n_{Sigma^{-}}=0.083pm 0.006pm 0.009ŗ}$ where the first error is statistical and the second is systematic. Differential cross-sections are also presented for the Σ+ and Σ− and compared with JETSET and HERWIG predictions. Assuming full isospin symmetry, the average inclusive rate is: ${1⩈er 3}[n_{Sigma^{+}+Sigma^{0}+Sigma^{-}}]=0.084pm 0.005 ({⤪ stat.}) pm 0.008 ({⤪ syst.})$.
The production of neutral kaons in e+e− annihilation at centre-of-mass energies in the region of the Z0 mass and their Bose-Einstein correlations are investigated with the OPAL detector at LEP. A total of about 1.26×106 Z0 hadronic decay events are used in the analysis. The production rate of K0 mesons is found to be 1.99±0.01±0.04 per hadronic event, where the first error is statistical and the second systematic. Both the rate and the differential cross section for K0 production are compared to the predictions of Monte Carlo generators. This comparison indicates that the fragmentation is too soft in bothJetset andHerwig. Bose-Einstein correlations in Ks0Ks0 pairs are measured through the quantityQ, the four momentum difference of the pair. A threshold enhancement is observed in Ks0Ks0 pairs originating from a mixed sample of\(K^0 \bar K^0\) and K0K0 (\(\bar K^0 \bar K^0\)) pairs. For the strength of the effect and for the radius of the emitting source we find values of λ=1.14±0.23±0.32 andR0=(0.76±0.10±0.11) fm respectively. The first error is statistical and the second systematic.
We have studied hadronic events produced at LEP at a centre-of-mass energy of 161 GeV. We present distributions of event shape variables, jet rates, charged particle momentum spectra and multiplicities. We determine the strong coupling strength to be αs(161 GeV) = 0.101±0.005(stat.)±0.007(syst.), the mean charged particle multiplicity to be 〈nch〉(161 GeV) = 24.46 ± 0.45(stat.) ± 0.44(syst.) and the position of the peak in the ξp = ln(1/xp) distribution to be ξ0(161 GeV) = 4.00 ±0.03(stat.)±0.04(syst.). These results are compared to data taken at lower centre-of-mass energies and to analytic QCD or Monte Carlo predictions. Our measured value of αs(161 GeV) is consistent with other measurements of αs. Within the current statistical and systematic uncertainties, the PYTHIA, HERWIG and ARIADNE QCD Monte Carlo models and analytic calculations are in overall agreement with our measurements. The COJETS QCD Monte Carlo is in general agreement with the data for momentum weighted distributions like Thrust, but predicts a significantly larger charged particle multiplicity than is observed experimentally.
The production of the $J^{P}={1⩈er 2}^{+}$ octet baryons Λ and Ξ−, the $J^{P}={3⩈er 2}^{+}$ decuplet baryons Σ(1385)±Ξ(1530)0, and Ω−, and the $J^{P}={3⩈er 2}^{-}$ orbitally excited state Λ(1520) has been measured in a sample of approximately 3.65 million hadronic Z0 decays. The integrated rates and the differential cross-sections as a function of xE, the scaled energy, are determined. The differential cross-sections of the Λ and Ξ− baryons are found to be softer than those predicted by both the JETSET and HERWIG Monte Carlo generators. The measured baryon yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is allowed. The yields are further compared with a thermodynamic model of hadron production which includes the production of orbitally excited mesons and baryons. The momentum spectra of Λ, Ξ−, Σ(1385)±Ξ(1530)0, and Λ(1520) are also compared to the predictions of an analytical QCD formula.
The full TASSO data have been used to study the inclusive production of strange mesons ine+e− annihilations. Differential and total cross sections have been measured in the centre of mass energy range 14 to 44 GeV forK0,\(\bar K^0\) and 34.5 to 44 GeV forK*± (892). We have investigated the strange meson production properties in jets by studying the rapidity andpt2 distributions as well as the evolution of the multiplicities as a function of the event sphericity. We find no evidence that the strange meson yields increase with increasing sphericity faster than the total charged multiplicity.
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