The inclusive cross section for the production ofKs0 mesons, Λ and\(\bar \Lambda\) particles in proton-proton interactions at\(\sqrt s= 63\) GeV is presented. The produced particles have been detected in the full phase space. Behaviour of the longitudinal and transversal depandences of the cross sections are discussed. The total production cross sections fors0 mesons and Λ particles was determined to\(\sigma _{{\rm K}_S^0 }= (25.5 \pm 1.4)\) mb andσΛ=(7.8±1.2) mb respectively. A strong energy dependence of the production cross sections is observed.
THE SIG(KS) ERROR INCLUDES THE UNCERTAINTY OF THE NORMALIZATION AND THE PT EXTRAPOLATION.
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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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Production of proton-antiproton pairs by two-photon scattering has been observed at the electron-position storage ring PETRA. A total of eight proton-antiproton pairs have been identified using the time-of-flight technique. We have measured a total cross section of 4.5 ± 0.8 nb in the photon-photon c.m. energy range 2.0–2.6 GeV.
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From the analysis of 5630 v υ and of 1372 v π charged current interactions, obtained in the BEBC bubble chamber filled with deuterium and exposed to the CERN wide band antineutrino beam, the ratios of cross section on neutron and photon targets have been measured and found to be R σ ν)/σ v p = 0.51 ± 0.01 (±0.03) , and R σ( ν n )/σ( v p ) = 22.2 ± 0.12 (±0.25) The dependence of these ratios on the x scaling variable shows, in a direct way, that the momentum distribution of the majority quark, u p ( x ) = d n ( x ), is broader than that of the minority quark, u n ( x ) = d p ( x ).
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Measurements of pp→μ+μ−+X at s=44 and 62 GeV are compared. The data are taken under identical conditions utilizing clean proton-proton collisions from the CERN intersecting storage rings and confirm scaling to 5%. The observed μ+μ− yield is a factor of 1.6±0.2 larger than estimated from a simple parton model but is consistent with QCD. The pT dependence of the muon pairs agrees well with expectations from QCD.
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We investigate the four-photon final state produced in γγ colissions. In the π 0 π 0 channel we observe f(1270) production with predominantly helicity 2 and measure a partial width Γ γγ 2.9 +0.6 −0.4 ± keV (independent of assumptions on the helicity). We observe A 2 (1310) production in the π 0 η channel and find a partial width Γ γγ = 0.77 ± 0.18 ± 0.27 KeV (assuming helicity 2). We give an upper limit for f ≈ ηη .
Data read from graph. Systematic error on M is of order of 2% or less.
Data read from graph.
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New measurements of thee + e − → π + π − π + π − cross section have been performed by the magnetic detector DM1 at DCI (ORSAY) in the 1.4−2.18 GeV total energy range with statistics of 11000 events. Assuming the4 π ± production is dominated by the ϱ′(1.6) we determine its parameters: M = 1.57 ± 0.02 (stat.) −0.00 +0.06 (syst.) GeV,Γ = 0.51 ± 0.04 (stat.) −0.01 +0.04 (syst.)GeV,Γ ρ ′ee B ϱ′→ ρ 0 π + π − = 2.67 ± 0.19 (stat.) −0.36 +0.27 (syst.)keV.
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The process e + e − → π 0 + anything has been measured at c.m. energies of 14 and 34 GeV for π 0 energies between 0.5 and 4 GeV. The ratio of π 0 to π ± production for π momenta between 0.5 and 1.5 GeV/ c is measured to be 2 σ ( π 0 )/ [ σ ( π + ) + σ ( π − )] = 1.3 ± 0.4 (1.2 ± 0.4) at 14 (34) GeV. The scaled cross section ( s / μ )d σ /d x when compared with lower energy (4.9–7.4 GeV) π 0 data indicates a substantial scaling violation.
COMPARISON OF PI0 WITH CHARGED PION CROSS SECTIONS (SCALED BI 1/S TO SAME ENERGIES).
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