The c.m. angular distribution of π+p elastic scattering at 1.6 GeV/c shows a strong forward diffraction peak decreasing exponentially with a slopeA + = (6.9±0.5) GeV−2 comparable to thatA − = (7.2±0.5) GeV−2 observed in a previous experiment for π-p elastic scattering at the same incident momentum. The behaviour of the π+ and the π− angular distributions is quite different beyond the diffraction peak. The π+p total elastic cross-section is found to be Σ01 = (16.70±0.45) mb.
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We present results on .~--p seattering at kinetic energies in the laboratory of 516, 616, 710, 887 and 1085MeV. The data were obtained by exposing a liquid hydrogen bubble chamber to a pion beam from the Saelay proton synchrotron Saturne. The chamber had a diameter of 20 cm and a depth of 10 cm. There was no magnetic field. Two cameras, 15 em apart, were situated at 84 cm from the center- of the chamber. A triple quadrnpole lens looking at an internal target, and a bending magnet, defined the beam, whose momentum spread was less than 2%. The value of the momentum was measured by the wire-orbit method and by time of flight technique, and the computed momentum spread was checked by means of a Cerenkov counter. The pictures were scanned twice for all pion interactions. 0nly those events with primaries at most 3 ~ off from the mean beam direction and with vertices inside a well defined fiducial volume, were considered. All not obviously inelastic events were measured and computed by means of a Mercury Ferranti computer. The elasticity of the event was established by eoplanarity and angular correlation of the outgoing tracks. We checked that no bias was introduced for elastic events with dip angles for the scattering plane of less than 80 ~ and with cosines of the scattering angles in the C.M.S. of less than 0.95. Figs. 1 to 5 show the angular distributions for elastic scattering, for all events with dip angles for the scattering plane less than 80 ~ . The solid curves represent a best fit to the differential cross section. The ratio of charged inelastic to elastic events, was obtained by comparing the number of inelastic scatterings to the areas under the solid curves which give the number of elastic seatterings.
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The polarization of the recoil proton in γ + p → p + π0 has been measured at photon energies of 725 MeV and 900 MeV for centerof-mass angles near 90° using a small propane-ethane gas bubble chamber. Protons emerging from a liquid hydrogen target are momentum-analysed with a magnet, and the scattering from carbon observed in the bubble chamber. A counter telescope rejects pions and electrons, and protons from multiple pion processes are discriminated against by keeping the peak bremsstrahlung energy just above the mean photon energy. The visual method of observing scattering asymmetries has the advantage of being insensitive to systematic asymmetries in the incoming proton flux. It also quickly eliminates strongly inelastic scatters (stars), and provides a complete angular distribution from which the fraction of scatters which are inelastic can be deduced. The effect of inelastic scatters upon the scattering asymmetry is large when the energy-loss resolution is poor, an inherent problem with bremsstrahlung beams. The counting rate for this small chamber (3.4g/cm2 carbon scatterer) was 11 scatters/hour using every 5th synchrotron pulse; larger chambers with more dense scatterers (such as Freon) could give higher counting rates. Results are fork = 725MeV and ϑ (pion) = 87° (cm.), P=0.74±0.20, and for k=900MeV and ϑ (pion) = 70°, P=.51±.7. P is taken to be positive along the directionK xp, wherep is the momentum of the outgoing proton.
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Using the internal beam of DESY elastic electron-proton cross-sections were measured at various angles between 32° and 130°, and with momentum transfers ofq 2=39, 60, 80 and 110 fm−2. Two single-quadrupole spectrometers, movable around a common liquid-hydrogen target, were used for analysing the momentum of the scattered electrons. Čerenkov and shower counters discriminated against pion and low-energy background. As a cross-section reference, recoil protons from elastic scattering atq 2=10 fm−2 were used, with a quantameter serving as an intermediate monitor. The data are consistent with the Rosenbluth formula, giving real form factorsG E andG M . Both continue to decrease with increasing momentum transfer, but somewhat faster than indicated by measurements performed so far.
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Measurements of π±p elastic differential cross-sections have been performed in the forward direction, using a missing-mass spark chamber spectrometer. The films have been seanned by an automatic apparatus. A phase-shift analysis of the experimental data has been done, leading to three solutions. Various experiments are proposed in order to resolve the ambiguities.
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An extensive investigation of antiproton-proton interactions at 5.7 GeV/c without strange-particle production was carried out using a hydrogen bubble chamber. Cross-sections for different channels are given and discussed. The reliability of the analysis was checked using artificially generated events. The cross-sections for elastic scattering, for all processes involving annihilation, and for all other inelastic processes are respectively σel=(16.3±0.6)mb,σannlbil=(22.5±2.0)mb, σinel=(24.8±2.0)mb. TheN * 1:38 is present both in the single and multiple pion production channels. For the reaction MediaObjects/11539_2007_Article_BF02720569_f1.jpg a cross-section of (1.05±0.21) mb was obtained. Cross-sections forN * 1238 production in other channels are also given. Some indication of the presence ofI=1/2 isobars was found in the nucleon-pion and the nucleon-two-pion systems. The inelastic nonannihilation reactions were found to be strongly peripheral. The one-pion exchange model including either a form factor or corrections for absorption was applied to the reaction MediaObjects/11539_2007_Article_BF02720569_f2.jpg . Neither version of the model could correctly account for all features of the reaction. The average number of pions in the annihilation was found to be 7.3±0.6. The presence of an asymmetry in the angular distribution of the charged pions was confirmed at this energy; it is due mostly to high-energy pions. The production of ρ and ω mesons was observed in various annihilation channels. Rates of up to 80% for ρ production and up to 15% for ω production were obtained by fitting phase-space and Breit-Wigner curves to the effective-mass distributions of different channels.
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The interactions of 720 MeV negative pions with protons were investigated using pictures from the 35 cm Saclay hydrogen bubble chamber. Partial cross-sections were determined with the following results: σ(elastic)=13.2±0.5) mb, σ(π−pπ0)=(5.25±0.30) mb, σ(π−π+n)=()7.17±0.35) mb σ (neutrals)=(9.9±0.7) mb, σ (2π production)=(1.03±0.13) mb. The elastic-scattering angular distribution was fitted with a fifth-order polynomial in cos θ* π which shows the effect of a significantF 5/2-D 5/2 interference contribution and predicts a value for (dσ/dΩ) (0°) in agreement with dispersion theory. For both single-π production channels, the two-body effective mass plots and c.m. angular distributions are presented, discussed and compared with the predictions from phase-space, the Olsson-Yodh isobar model and the pole model of isobar production. TheN *(3/2, 3/2) isobar is seen to play an important role in the ππN final states, but the agreement of the data with the existing isobar models and their assumptions is not satisfactory. A comparison of the different two-pion production cross-sections π−pπ−π+, π−pπ0π0 and π−π+nπ0 suggests a strong contribution of π−p→η0n to the π−π+nπ0 final state. An upper limit for σ(π−p→η0n) of (3.0±0.4) mb was obtained.
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Photoproduction cross-section of the η-particle for incident photon energiesK from ∼800 to ∼1000 MeV has been measured at the 1.1 GeV Frascati electronsynchrotron. The differential cross-section for this process, at a c.m. angle of the η of ∼110°, turns out to be fairly constant for 830 MeV≤K≤900 MeV, and drops down by a factor 5 to 10 atK=950 MeV. These results are discussed in terms of a comparison with the data on the production of η's by pions, and with the data on pion-nucleon scattering and pion photoproduction. The conclusions are in agreement with the hypothesis that the η-N system is dominated at low energies by a resonance with orbital angular momentuml=0 (S 1/2,1/2 resonance).
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Cross-sections for the photoproduction of positive pions in hydrogen have been measured at the 1.1 GeV Frascati electron synchrotron for photon energiesE γ between 500 and 800 MeV and for π+ c.m. angles of θ=30o, 90o. The cross-sections exhibit a smooth behavior as a function of energy forE γ=(500÷600) MeV. No immediate evidence is found of a contribution of theP 11 resonance.
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