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perimental analysis of the process is presented. Theσ(−)/σ(+) ratio has been measured in the photon energy interval (170÷230) MeV and Lab. angles 45°, 75°, 105°, 150°. The results are interpreted on the base of the impulse approximation with the aim of getting information on the processhv+n →π −+p.
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The differential cross section for the gamma +n --> pi- + p and the gamma + p --> pi+ n processes were measured at Jefferson Lab. The photon energies ranged from 1.1 to 5.5 GeV, corresponding to center-of-mass energies from 1.7 to 3.4 GeV. The pion center-of-mass angles varied from 50 degree to 110 degree. The pi- and pi+ photoproduction data both exhibit a global scaling behavior at high energies and high transverse momenta, consistent with the constituent counting rule prediction and the existing pi+ data. The data suggest possible substructure of the scaling behavior, which might be oscillations around the scaling value. The data show an enhancement in the scaled cross section at center-of-mass energy near 2.2 GeV. The differential cross section ratios at high energies and high transverse momenta can be described by calculations based on one-hard-gluon-exchange diagrams.
Differential cross section for the process GAMMA N --> PI- P for an incident electron energy of 5.614 GeV.
Differential cross section for the process GAMMA N --> PI- P for an incident electron energy of 4.236 GeV.
Differential cross section for the process GAMMA N --> PI- P for an incident electron energy of 3.400 GeV.
Differential cross sections for π−p→γn have been determined from 427 to 625 MeV/c, mainly at 90° and 110° c.m. The data were obtained by combining measurements of the Panofsky ratio in flight with known charge-exchange cross sections. The results are compared with γn→π−p data derived from γd experiments; the difference is typically 30%. The radiative decay amplitudes of neutral πN resonances are therefore uncertain by at least 30%.
Charge exchange cross section from PWA.
PI- P --> GAMMA N cross section.
GAMMA N --> PI- P cross section calculated using detailed balance.
π−-photoproduction cross sections from neutrons have been measured with a deuterium target at effective γ-energies from 900 to 1,800 MeV and pion centre-of-mass angles 65 to 125°. The outgoing pion and proton were detected in coincidence, the pion with a magnetic spectrometer and the proton with a time-of-flight system. To test the reliability of the analysis method, a comparison of π+-photoproduction from protons and deuterons was made with a slightly modified apparatus. It was found adequate to use the spectator model with a Huthèn wave function.
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Axis error includes +- 10./10. contribution (DUE TO BEAM POLARIZATION UNCERTAINTY).
D(SIG)/D(OMEGA)=(D(SIG(O))/D(OMEGA)+D(SIG(C))/D(OMEGA))/2, WHERE (O) AND (C) DENOTES GAMMA POLARIZATION ORTHOGONAL AND COPLANAR TO THE REACTION PLANE.
Axis error includes +- 10./10. contribution (DUE TO BEAM POLARIZATION UNCERTAINTY).
The asymmetries in forward π−N, π−Δ, and K+−(Λ+Σ) photoproduction have been measured with a 16-GeV linearly polarized beam. The experimental method and the procedures for extracting cross sections and asymmetries from the data are discussed in detail. Information on the energy and momentum-transfer dependence of cross sections for natural- and unnatural-parity exchange, interference between exchanges of opposite G parity, and vector-meson dominance is obtained and discussed.
ASYMMETRIES AND DIFFERENTIAL CROSS SECTIONS FOR PION-NUCLEON PHOTOPRODUCTION WERE FIRST PUBLISHED IN D. J. SHERDEN ET AL., PRL 30, 1230 (1973) AND PRL 31, 667 (1973) (ERRATUM). THESE SLIGHTLY REVISED NUMBERS ARE INCLUDED IN THE RECORD OF THE 1973 PAPER.
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The differential cross sections for γ p→ π + n from hydrogen and the π − π + ratios from deuterium were measured at nine c.m. angles between 30° and 150° for laboratory photon energies between 260 and 800 MeV. A magnetic spectrometer with three layers of scintillation hodoscope was used to detect charged π mesons. The cross section for γ n→ π − p was obtained as a product of d σ d Ω (γ p →π + n ) and the π − π + ratio. The overall features in the cross sections of the two reactions, γ p→ π + n and γ n→ π − p, and in the ratios, π − π + , agree with predictions by Moorhouse, Oberlack and Rosenfeld, and Metcalf and Walker. An investigation of the possible existence of an isotensor current was made and a negative result was found. In detailed balance comparison with the new results on the inverse reaction π − p→ γ n, no apparent violation of time-reversal invariance was observed.
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