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Evidence for narrow resonant structures at $W \approx 1.68$ and $W \approx 1.72$ 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 $E_γ=0.85 - 1.25$ GeV is presented. The data reveals two narrow structures at $E_γ= 1.036$ and $E_γ=1.119$ GeV. They may signal narrow resonances with masses near $1.68$ and $1.72$ GeV, or they may be generated by the sub-threshold $KΛ$ and $ωp$ production. Their decisive identification requires additional theoretical and experimental efforts.