We present data on inclusive and semi-inclusive ϱ 0 production in 147 GeV/ c π − p interactions. We find a total cross section of 7.3 ± 1.3 mb. Most of this cross section is found in the lower topology events (⩽ 10 prongs), and in the central and forward rapidity regions. The P T 2 dependence of ϱ 0 production, 〈: n > ϱ 0 per event, and the ϱ 0 / π + ratios are also discussed.
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We have investigated inclusive Λ , Λ and Σ ± (1385) productions in 405 GeV/ c pp interactions. The observed cross sections are σ ( Λ )=4.05±0.39 mb, σ( Λ =0.63±0.17 mb, σ ( Σ + (1385))=0.74±0.17 mb and σ ( Λ − (1385))=0.56±0.17 mb. Λ production is dominant in a central region of ∣ x ∣≤0.4. The Λ/ Λ production ratio at ∣ x ∣≈0 is found to be 1.2±0.5. The excess, about 0.2 mb, of σ ( Λ + (1385)) over σ ( Λ − (1385)) is most likely attributed to proton fragmentations (∣ x ∣≥0.4), and gives an evidence for scaling.
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We present new high statistics data on hadron production in photon-photon reactions. The data are analyzed in terms of an electron-photon scattering formalism. The dependence of the total cross section of Q 2 , the four-momentum transfer squared of the scattered electron, and on the mass W of the hadronic system is investigated. The data are compared to predictions from Vector-Meson Dominance and the quark model.
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DEPENDENCE ON VISIBLE HADRONIC INVARIANT MASS.
Data read from graph.
Results on inclusive production of γ,K n , Λ 0 and Λ 0 in K − p interactions at 110 GeV/ c are presented. Total cross sections, and differential cross sections in terms of Feynman x , rapidity and p T 2 are given. It is found that about 40% of K n 's are produced together with a strange particle pair, and that 80% of Λ 0 's are produced together with a K K pair. These Λ 0, 's are produced predominantly in the backward direction. Fits to the form (1−| x |) n to the x F distributions of K n and Λ 0 in the fragmentation regions are found to be in general agreement with quark counting rule predictions.
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The final states of charged hadrons produced in 280 GeV μp scattering are analysed with respect to their planarity and jet structure. Distributions of p ⊥ 2 in and p ⊥ out 2 are presented. A two jet structure in the forward hemisphere is observed for events with high p ⊥ tracks are predicted by QCD models.
PTIN**2 is the sum of the PTIN components squared.
PTOUT**2 is the sum of the PTOUT components squared.
Total and differential cross sections ofK*−(890),K*−(890),\(\bar K^{ * 0} \)(890),K*0(890),\(\bar K^{ * 0} \)(1430) andϱ0(770) produced inK−p interactions at 110 GeV/c are presented. The cross sections of the neutral resonances show a smooth increase with energy from 10 to 110 GeV/c incident momentum. For theK*+(890) and theK*0(890), i.e. the resonances with strangenessS=+1, this rise is quite significant: their cross sections practically double between 32 GeV/c and 110 GeV/c incidentK− momentum. About 50% of the neutral kaons and 30% of charged pions produced inK−p interactions at our energy are found to be decay products of the resonances considered.
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The production of J/ ϑ and ϑ′ has been measured in 250 GeV muon iron interactions. The measured total cross sections are σ ( μ N → μ J/ ϑ X)=0.74±0.14 nb and σ ( μ N → μϑ ′X)=0.16 ± 0.07 nb. An upper limit on the cross section times branching ratio for ϒ production of BR · σ ( μ N → μϒ X) < 5.2 × 10 −38 cm 2 (at 90% confidence level) is obtained. About half the J/ ϑ cross section is found to have Z ⩾ 0.95 (where Z = E (J/ ϑ / ν ). The first-order photon-gluon fusion model agrees well with the measured Q 2 and ν dependence of the J/ ϑ data and is used to extract the gluon momentum distribution. However, higher order QCD effects are needed to explain the Z distribution of the J/ ϑ and the observed broadening of the P t 2 distribution with decreasing Z . The decay angular distributions of the J/ ϑ are found to be flat in the s -channel frame, but there is evidence for polarisation in the t -channel frame.
NUMBERS ARE CROSS-SECTIONS FOR PSI AND PSI(PRIME) BUT CROSS-SECTION*BR.RATIO FOR THE UPSILON.
THE COHERENT PRODUCTION IS NOT SUBTRACTED.
THE COHERENT PRODUCTION IS SUBTRACTED.
Dimuon and trimuon events produced by the interaction of 250 GeV muons in an iron target have been studied and are shown to originate predominantly from charm production. The data are used to measure the contribution of charm to the nucleon structure function F 2 . The cross sections for real photoproduction ( Q 2 =0) of charm in the current fragmentation region are derived as a function of photon energy and are found to be ∼0.6% of the total, hadronic photoproduction cross section in this energy range. The measured cross sections are found to be well represented by the photon-gluon fusion model. The charmed quark fragmentation function is obtained by using this model to fit the measured decay muon energy distribution and is found to be well represented by exp(1.6±1.6) Z . The data are used to study the momentum distribution of the gluons in the nucleon. An upper limit of 1.4% (90% confidence level) is set on the branching ratio D→ μν and a model-dependent upper limit on the branching ratio F→ μν is derived.
The charm contribution to the nucleon structure function from the dimuon data.
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Identification of muons in hadronic events from e+e− annihilation observed in the MAC detector at the storage ring PEP provides flavor tagging of heavy primary quarks. A sample enriched in events from bb¯ production is obtained and the b-quark fragmentation function is inferred from the momentum spectrum of the muons. The b quark is found to fragment predominantly with high values of z, with 〈zb〉=0.8±0.1, and to have an over-all semimuonic branching fraction of (15.5−2.9+5.4)%.
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