Measurements on large-angle photoproduction of π+ mesons from hydrogen have been made at the Stanford Linear Accelerator Center for photon energies between 5 and 15.5 GeV and u values from +0.05 to -1.8 (GeV/c)2. The measured cross section decreased with energy approximately as k−3, showing no shrinkage in this range of u values. Furthermore, it had a smooth u dependence with no sign of a dip at u≃−0.15 (GeV/c)2 as would be expected from nucleon exchange. π−Δ++ production was measured at 5 GeV and shows a rapid decrease with increasing |u|.
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Cross sections for π0 photoproduction from hydrogen in the backward direction have been measured for photon energies of 6, 8, 12, and 18 GeV. The range of momentum transfer covered in these measurements is −1 (GeVc)2<u<0(GeVc)2, dσdu is found to have a backward peak and decreases with energy as s−3.0±0.2. Photoproduction of η0 and ρ0 mesons has also been observed.
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We have investigated the photoproduction process γ+p→π++n over a wide range of energies and u values at the Stanford Linear Accelerator Center (SLAC) accelerator. We also have investigated γ+p→π−+N*++ at one value of u and γ+p→K++Λ0, Σ0 at one u value and three energies. Our results for dσdu for the photoproduction of π+ mesons from hydrogen are roughly α2π of the corresponding cross sections for the elastic scattering of π− mesons from hydrogen. The u dependence of our cross sections is not dominated by nucleon exchange as it is in the case of π+p elastic scattering.
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We report measurements of the photoproduction from hydrogen of single π+ mesons at gamma-ray energies of 3.4 and 5.0 BeV and at laboratory angles of 5.1°, 7.1°, 9.9°, and 15.1°. The s dependence at fixed t is derived for momentum transfers of -0.20, -0.37, and -0.70 BeV2. The pion data are compared with a Reggeized one-pion-exchange model.
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The target asymmetry T, recoil asymmetry P, and beam-target double polarization observable H were determined in exclusive $\pi ^0$ and $\eta $ photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the $\gamma p \rightarrow \pi ^0 p$ and $\gamma p \rightarrow \eta p$ reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the $\eta n$ system at $W = 1.68\ \textrm{GeV}$. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the $S_{11}(1535)$ and $S_{11}(1650)$ resonances within the $S_{11}$-partial wave.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma p \to \pi^0 p$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma n \to \pi^0 n$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma p \to \eta p$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
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