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The π0 photoproduction cross section has been measured at 180° for photon energies from 220 to 380 MeV, in steps of 20 MeV, by detecting the recoil proton at 0°. The statistical accuracy of the measurements varies between 3 and 7%, depending on the energy. Absolute cross sections have been deduced from a comparison of the measurements with electron-proton scattering. The experimental data are compared with theoretical results calculated from fixed-momentum-transfer dispersion relations. Special attention is paid to the prediction of the multipoles at the first resonance, namely, E1+32, M1+32, and E0+π0 to obtain agreement with experiment.
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Accurate measurements have been made of the π−π+ photoproduction ratio on deuterium, in the gammaray energy range 165-210 MeV, for several angles: 155°, 125°, 90° (center-of-mass system) and along Baldin's kinematical line. These last data are new contributions: π−π+=1.20±0.03 averaged between 165 and 180 MeV. The others are improvements of the accuracy of previous data. The comparison with Ball's theory, corrected for taking into account the I=12 phase shifts, gives for the coupling constant Λ for γ−π−p the value: 0.25<+Λe<0.75.
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We present a new measurement of the total photoproduction cross section performed with the H1 detector at HERA. For an average centre of mass energy of 200GeV a value of $\sigma_{tot}~{\gamma{p}}= 165\pm2\pm11\mu$b has been obtained. A detailed analysis of the data in adequate kinematic regions enabled a decomposition of the total cross section in its elastic, single diffractive dissociation and remaining non-diffractive parts, based on safe assumptions on the double diffractive dissociation contribution.
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Total GAMMA P cross section.
We have measured transverse momentum spectra up to 10 GeV/ c for charged particles produced centrally in proton-antiproton collisions at 540 GeV in the centre of mass at the CERN collider. Our results are compared with data at ISR energies and with the predictions of a QCD model. The charged particle spectrum shows a clear dependence on charged track multiplicity.
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We report on an improved measurement of the value of the strong coupling constant σ s at the Z 0 peak, using the asymmetry of the energy-energy correlation function. The analysis, based on second-order perturbation theory and a data sample of about 145000 multihadronic Z 0 decays, yields α s ( M z 0 = 0.118±0.001(stat.)±0.003(exp.syst.) −0.004 +0.0009 (theor. syst.), where the theoretical systematic error accounts for uncertainties due to hadronization, the choice of the renormalization scale and unknown higher-order terms. We adjust the parameters of a second-order matrix element Monte Carlo followed by string hadronization to best describe the energy correlation and other hadronic Z 0 decay data. The α s result obtained from this second-order Monte Carlo is found to be unreliable if values of the renormalization scale smaller than about 0.15 E cm are used in the generator.
Value of LAMBDA(MSBAR) and ALPHA_S.. The first systematic error is experimental, the second is from theory.
The EEC and its asymmetry at the hadron level, unfolded for initial-state radiation and for detector acceptance and resolution. Errors include full statistical and systematic uncertainties.
The elastic scattering of K+ mesons on protons is studied at 3.5 and 5 GeV/c. The total elastic cross-sections are found to be (4.36±0.36) mb and (3.82±0.41) mb respectively. The differential elastic cross-sections, which exhibit characteristic diffraction peaks, are fitted by dσ/dt=(dσ/dt)0eαt, giving α=(3.85±0.12) and (4.70±0.21) (GeV/c)−2 for the two momenta respectively, with |t|⪝0.65 (GeV/c)2. The results are compared to those at neighbouring energies, giving some support to the presence of a real part of the forward scattering amplitude. The diffraction peak shows definite shrinking with increasing momenta. The data are examined in the light of models for high-energy scattering.
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BEBC filled in turn with hydrogen, and with a neon-hydrogen mixture, was exposed to the CERN SPS wide band neutrino and antineutrino beams. The ratios of the charged-current cross sections per nucleon, σ(νH 2 ) σ(ν Ne ) and σ( ν H 2 ) σ( ν Ne ) , between 20 and 300 GeV were found to be 0.656 ± 0.020 and 1.425 ± 0.052, respectively. Multiplying these ratios by the revised cross sections in neon, σ(ν Ne ) E = (0.723 ± 0.038) × 10 −38 cm 2 / GeV per nucleon and σ( ν Ne ) E = (0.351 ± 0.019) × 10 −38 cm 2 / GeV per nucleon, and their ratio, σ( ν Ne ) σ(ν Ne ) = 0.485 ± 0.020 ,, yields values for the total charged-current cross sections on protons, σ(νp)/ E and σ( ν p ) E , of (0.474 ± 0.029) × 10 −38 cm 2 /GeV and (0.500 ± 0.032) × 10 −38 cm 2 /GeV. respectively, and a value for the ratio σ( ν p ) σ(ν p ) of 1.053 ± 0.066.
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