Photoproduction of Eta Mesons from Hydrogen at 0° and 180° for Energies Between 0.7 and 1.1 Gev
<p>We have measured, using the Caltech 1.5-GeV electron synchrotron, the cross section for γp → pη(η → γγ) at 0° and 180 in the energy range 0.7 to 1.1 GeV. Two totally-absorbing lead glass Cherenkov counters detected both photons from the decay η → γγ, while the recoil proton went undetected...
| Summary: | <p>We have measured, using the Caltech 1.5-GeV electron synchrotron, the cross section for γp → pη(η → γγ) at 0° and 180 in the energy range 0.7 to 1.1 GeV. Two totally-absorbing lead glass Cherenkov counters detected both photons from the decay η → γγ, while the recoil proton went undetected. Eta events produced a peak in the di-photon energy spectrum of the two counters. Approximately 100,000 eta events were identified using a background subtraction procedure.</p>
<p>The energy of the incident photon was not well resolved experimentally, which made the cross section evaluation difficult. One method of evaluation localizes the incident photon energy artificially by forming appropriate linear combinations of the physical measurements. An alternate method parametrizes the cross section as a smooth function of energy and fits the physically measured yield of eta events. The two methods agree tolerably well.</p>
<p>A significant departure from angular isotropy in the cross section is observed starting at about 0.8 GeV, with the backward cross section dominating the forward cross section. We interpret this result, plus recent measurements of the recoil proton polarization, in the framework of a simple resonance model. Tentative upper limits are set for the contributions of the states P₁₁(1460) and S₁₁(1710) to the amplitude for eta photoproduction.</p> |
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