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Photoproduction is studied at 2.8 and 4.7 GeV using a linearly polarized monoenergetic photon beam in a hydrogen bubble chamber. We discuss the experimental procedure, the determination of channel cross sections, and the analysis of the channel γp→pπ+π−. A model-independent analysis of the ρ0-decay angular distribution allows us to measure nine independent density-matrix elements. From these we find that the reaction γp→pρ0 proceeds almost completely through natural parity exchange for squared momentum transfers |t|<1 GeV2 and that the ρ production mechanism is consistent with s-channel c.m. helicity conservation for |t|<0.4 GeV2. A cross section for the production of π+π− pairs in the s-channel c.m. helicity-conserving p-wave state is determined. The ρ mass shape is studied as a function of momentum transfer and is found to be inconsistent with a t-independent Ross-Stodolsky factor. Using a t-dependent parametrization of the ρ0 mass shape we derive a phenomenological ρ0 cross section. We compare our phenomenological ρ0 cross section with other experiments and find good agreement for 0.05<|t|<1 GeV2. We discuss the discrepancies in the various determinations of the forward differential cross section. We study models for ρ0 photoproduction and find that the Söding model best describes the data. Using the Söding model we determine a ρ0 cross section. We determine cross sections and nine density-matrix elements for γp→Δ++π−. The parity asymmetry for Δ++ production is incompatible with simple one-pion exchange. We compare Δ++ production with models.
FROM QUOTED TOPOLOGICAL CROSS SECTIONS. 1.44 GEV CROSS SECTION PUBLISHED PREVIOUSLY.
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NO TMIN CORRECTION HAS BEEN MADE.
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STATISTICAL ERRORS ONLY.
For the reaction γ p → K + Λ 0 the differential cross section has been measured at t = −0.147 GeV 2 ( θ C.M. = 26.5 ± 3.5°) and photoenergies between 1.05 and 2.2 GeV and for the reaction γ p→K + Σ 0 at ≈−0.17 GeV 2 ( θ C.M. = 28±3.5°) and photoenergies between 1.3 and 2.2 GeV. For this four momentum transfer the differential cross section of K + Λ 0 photoproduction has a surprising steep increase above threshold and stays nearly constant up to 2.2 GeV. The K + Σ 0 cross section increases from 1.3 to 1.56 GeV and goes down gradually at higher energies.
AT CONSTANT MOMENTUM TRANSFER OF -T = 0.147 GEV**2.
AT APPROXIMATELY CONSTANT MOMENTUM TRANSFER OF -T = 0.17 GEV**2.
The π−+p→π0+n differential cross section at 180° has been measured for 52 values of π− momentum from 1.8 to 6.0 GeV/c using a constant-geometry detection system. The average statistical uncertainty is ∼5% and the systematic uncertainty is ∼10%. The details of the experiment and the data analysis are discussed. The data are compared with those of other experiments with which they are generally in agreement. One set of data disagrees with those presented here and a possible reason for this is discussed. A five-parameter fit of the predictions of a dual-resonance model to our data gave excellent agreement. The differential cross sections at 180° for π±p elastic scattering have been compiled and the moduli and relative phase of the T=12 and T=32 pion-nucleon s- and u-channel amplitudes (|A12|, |A32|, and cosδ) have a minimum at u=0.4 GeV/c and, in the s channel, a corresponding minimum at s=2.2 GeV/c.
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The differential cross section has been measured for the reaction γ +p→p+ π o at the Bonn 2.5 GeV electron synchrotron in the energy range from 0.4 to 2.2 GeV for a c.m. angle of 150 degrees. The protons were detected in a magnetic spectrometer system. The excitation curve shows a distinct resonance structure. The total corrections to the counting rate are about 3%. The contribution of the process γ +p→p+2 π was separated. The uncertainty of this separation leads to an error of about 4% in the cross section.
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The target asymmetry T = ( σ ↑ − σ ↓)/( σ ↑ + σ ↓) for the reaction γ p → π + n has been measured at the Bonn 2.5 GeV electron synchrotron for a pion c.m. angle of 40° and γ energies between 0.5 and 2.2 GeV. Butanol was used as the target material. About 35% of the protons could be polarized using the dynamic-polarization method in a continuous-flow cryostat operating at 1°K and 25 kG. The π + mesons were detected in a magnetic-spectrometer system. Considerable structure in the asymmetry was observed.
Axis error includes +- 11/11 contribution.
The electroproduction of a π-meson and of a Δ(1236) nucleon resonance on hydrogen, ep → e πΔ (1236), was investigated in the two charge states π − Δ ++ and π + Δ 0 by measuring the scattered lepton and the produced π-meson in coincidence. The differential cross sections as funcions of W , q 2 , t − t min and ø πq were determine in the following kinematical region: w = (π + δ) 2 = 2.0 − 3.0 GeV , |q 2 | = |(e−e′) 2 | = 0.15 − 0.8 GeV 2 /c 2 , |t − t min | = 0-0.5 GeV 2 /c 2 with t = ( p − δ) 2 , φ πq = 0 − 360° .
W-DEPENDENCE FOR 4.0 GEV INCIDENT POSITRONS.
W-DEPENDENCE FOR 4.9 GEV INCIDENT POSITRONS.
W-DEPENDENCE FOR 5.4 GEV INCIDENT POSITRONS.
Results are presented on the elastic scattering of photons by protons. The incident photon energy ranged from 0.55 GeV to 4.5 GeV, and the four-momentum transfer t ranged from 0.12 to 1.0 (GeV/c)2. The data at large angles, 60°<θ*<115°, are characterized by a pronounced excitation of the D13(1518) resonance, a shoulder in the 1688-MeV mass region, and a precipitous drop thereafter in the cross section as a function of incident energy. The low-t data are characterized by a diffraction slope of 5 (GeV/c)−2. The data are inconsistent with the predictions of the vector-dominance model if the latter is restricted to ρ0, ω, and φ vector mesons.
No description provided.
The analysis of 1466 events of the type e + e − → μ ± μ ± , in the time-lifke range from 1.44 to 9.00 GeV 2 , sh that the absolute value of the cross-section and its energy dependence follow QED expectations within (± 3.2%) and (± 1.2%), respectively.
The cross section of the reaction $e^+ e^- \to \mu^\pm \mu^\mp$ integrated over the experimental apparatus at 14 values of the colliding beam energy $E$ corresponding to total centre-of-mass energy $\sqrt{s}=2E$ from 1.2 to 3.0 GeV.
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