The inclusive production cross sections of η′ (958) andfo (975) mesons are measured ine+e− annihilation in the nonresonant continuum around\(\sqrt s= 10\) GeV and in decays of the υ resonances using the ARGUS detector. For η′ (958) mesons, a production ratio of η′ (958)/ηdir=0.35±0.24, with ηdir=η−BR(η′→ηX)·η′, is determined in direct υ(1S) decays, which can be partially explained by the pseudoscalar singlet/octet mixing. Forfo(975) production, we obtain a production ratio offo(975)/p(770)°=0.17±0.030 in direct υ(1S) decays. In its production features, thefo(975) behaves like an ordinary meson, though aK\(\bar K\) molecule nature cannot be excluded. The substantial production yield of thefo(975) meson demonstrates the important effect of feeddown from mesons beyond the basic multiples on pseudoscalar and vector meson production.
Direct etaprime rates per event for the continuum region (9.36 to 10.45 GeV), the UPSI(1S) (9.46 GeV), UPSI(2S)(10.02 GeV) and UPSI(4S)(10.58 GeV) regions. Data is extrapolated to the full z region.
Radiation corrected normalized cross section for F0(975) production in the continuum events.
Normalized cross section for F0(975) production in direct UPSI(1S) decays.
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.
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We have studied single diffraction dissociation ( p p→ p X ) in proton-antiproton collisions at √ s =1.8TeV, covering the ranges 3⪅ M X ⪅200 GeV and 0.05⪅| t |⪅0.11 (GeV/ c ) 2 . Parameterizing the production to be of the form dσ ( d t d M 2 X ) = (M 2 X ) −α exp (bt) , we obtain α = 1.13±0.07 and b = 10.5±1.8(GeV/ c ) −2 . The total single diffraction dissociation cross section is 2 σ SD =8.1±1.7 mb. Comparisons are made to previous lower energy data, and to an earlier measurement by us at the same energy.
Total single diffraction cross section.
We present measurements from events with two isolated prompt photons in p¯p collisions at √s =1.8 TeV. The differential cross section, measured as a function of transverse momentum (PT) of each photon, is about 3 times what next-to-leading-order QCD calculations predict. The cross section for photons with PT in the range 10–19 GeV is 86±27(stat)−23+32(syst) pb. We also study the correlation between the two photons in both azimuthal angle and PT. The magnitude of the vector sum of the transverse momenta of both photons, KT=‖PT1+PT2‖, has a mean value of 〈KT〉=5.1±1.1 GeV.
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Vector sum of the photons transvserse momenta.. Errors contain both statistics and systematics.. Data read from plots.
Observation of the semileptonic decay of the charmed baryon in the decay channel has been made using the ARGUS detector at the e + e − storage ring DORIS II at DESY. The cross section times branching ratio was found to be .
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Averaging the above two results.
The cross section and jet rates ofZ0 decays into photons and quarks are compared with matrix element Monte Carlos ofO(ααs). Good agreement is found between data and theoretical predic
Corrected number of hadronc events that have a final state photon per 1000 multhadronic Z0 decays, using the E0 scheme.
Corrected number of hadronc events that have a final state photon per 1000 multhadronic Z0 decays, using the Durham scheme.
Corrected number of events that have a final state photon with 1, 2, 3, or more jets per 1000 multhadronic Z0 decays, using the E0 scheme.
We present first results on the total photoproduction cross section measurement with the H1 detector at HERA. The data were extracted from low Q 2 collisions of 26.7 GeV electrons with 820 GeV protons. The γp total cross section has been measured by two independent methods in the γp center of mass energy range from 90 to 290 GeV. For an average center of mass energy of 195 GeV a value of σ tot ( γp ) = 159 ± 7 (stat.) ± 20 (syst.) μb was obtained.
Data from tagged sample.
Data from untagged sample.
A study of inclusive production of the meson resonances ρ 0 , K ∗0 (892), ƒ 0 (975) and ƒ 2 (1270) in hadronic decays of the Z 0 is presented. The measured mean meson multiplicity per hadronic event is 0.83 ± 0.14 for the ρ 0 0.64 ± 0.24 for the K ∗0 (892), 0.10 ± 0.04 for the ƒ 0 (975) in the momentum range p > 0.05 p beam ( x p > 0.05) and 0.11 ± 0.05 for the ƒ 2 (1270) for x p > 0.1 . These values and the corresponding differential cross sections ( 1 σ hadr ) d σ d x p for the vector mesons are in good agreement with the predictions of the JETSET 7.3 PS and HERWIG 5.4 models. The ƒ 2 (1270) production is overestimated by HERWIG but its x p -shape is correctly reproduced. The measured ratios of the production cross sections σ(ƒ 2 (1270)) σ(ρ 0 ) = 0.22 ± 0.08 and σ(ƒ 2 (1270)) σ(ƒ 0 (975)) = 3 −1 +7 for x p > 0.1 are consistent with the results obtained in hadronic reactions.
Average multiplicity per hadronic event. Extrapolation to x = 0 using the x shape predicted by JETSET 7.3 PS.
Average multiplicity per hadronic event. Extrapolation to x = 0 using the x shape predicted by JETSET 7.3 PS.
Average multiplicity per hadronic event. Extrapolation to x = 0 using the x shape predicted by JETSET 7.3 PS.
We report a study of electron proton collisions at very low Q 2 , corresponding to virtual photoproduction at centre of mass energies in the range 100–295 GeV. The distribution in transverse energy of the observed hadrons is much harder than can be explained by soft processes. Some of the events show back-to-back two-jet production at the rate and with the characteristics expected from hard two-body scattering. A subset of the two-jet events have energy in the electron direction consistent with that expected from the photon remnant in resolved photon processes.
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The total photoproduction cross section is determined from a measurement of electroproduction with the ZEUS detector at HERA. The Q 2 values of the virtual photons are in the range 10 −7 < Q 2 <2×10 −2 GeV 2 . The γp total cross section in the γp centre of mass energy range 186–233 GeV is 154 ± 16 (stat.) ± 32 (syst.) μ b.
Scattered electron in range 10 to 16 GeV.
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