The differential cross section for the reaction γp → π 0 p at forward angles has been measured in the energy region between 350 MeV and 1175 MeV. A phenomenological multiple analysis was carried out on the present data together with other data.
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We have measured the ratio of the cross section for γ+n→π0+n to the cross section for γ+p→π0+p at 4.7 and 8.2 GeV. The measurements were made by detecting the recoil nucleons in coincidence with the decay γ rays of the π0's produced from a deuterium target. At 4.7 GeV the cross-section ratio, R≡σ(γ+n→π0+n)σ(γ+p→π0+p), is less than 1.0 at low t, with an indication of a dip at about t=−0.7(GeVc)2, and rises to 1.0 at high t. The ratios at the higher energy have less structure and are uniformly closer to 1.0.
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Measurements are presented of the recoil-proton polarization for π0 photoproduction angles near 64° in the c.m. system. The steep angular dependence observed by others at lower energies persists to at least 1500 MeV, and the polarization crosses through zero near 63° over the entire 900-1600-MeV energy interval. Summary fits are made to available recoil-proton polarization data, 950-1250 MeV, and are found to require terms of order cos3θ, but no higher.
Axis error includes +- 0.0/0.0 contribution (?////).
Electron-proton elastic-scattering cross sections have been measured at the Stanford Linear Accelerator Center for four-momentum transfers squared q 2 from 1.0 to 25.0 (GeVc)2. The electric (GEp) and magnetic (GMp) form factors of the proton were not separated, since angular distributions were not measured at each q 2. However, values for GMp were derived assuming various relations between GEp and GMp. Several theoretical models for the behavior of the proton magnetic form factor at high values of q 2 are compared with the data.
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The photoproduction yields of π0 mesons from D2, Be, C, Al, Cu, Ag, and Pb targets have been measured at peak bremsstrahlung energies of 4.25, 5.6, 7.8, and 9.6 GeV. The A dependence of π0 photoproduction is found to be almost independent of energy in this range in contrast to vector-meson dominance predictions.
A-EFFECTIVE IS SIG(GAMMA A --> PI0 A)/SIG(GAMMA NUCLEON --> PI0 NUCLEON). IT IS NORMALIZED RELATIVE TO THE VALUE FOR DEUTERIUM WHICH IS CALCULATED WITH GLAUBER CORRECTIONS.
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The differential cross sections for the γ + n → π O + n reaction have been measured at the photon energies of 500–900 MeV. The ratios, R oo = [ d δ d Ω(γ n → π o n ) ] [ d δ d Ω(γ p → π o p ) ] , have been obtained at the c.m. pion angles of 60 O , 90 O , 105 O , 120 O , and 140 O .
Axis error includes +- 0.0/0.0 contribution (8 TO 11////).
Axis error includes +- 0.0/0.0 contribution (8 TO 11////).
Axis error includes +- 0.0/0.0 contribution (8 TO 11////).
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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