Evidence for narrow resonant structures at W ≈ 1.68 GeV and W ≈ 1.72 GeV in real Compton scattering off the proton.

First measurement of the beam asymmetry Σ for Compton scattering off the proton in the energy range Ey = 0.85-1.25 GeV is presented. The data reveal two narrow structures at Er = 1.036 and Ey = 1.119 GeV. They may signal narrow resonances with masses near 1.68 and 1.72 GeV, or they may be generated by the subthreshold K A and cop production. Their decisive identification requires additional theoretical and experimental efforts. [ABSTRACT FROM AUTHOR]