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 $\\ensuremath{\\Sigma}$ for Compton scattering off the proton in the energy range ${E}_{\\ensuremath{\\gamma}}=0.85--1.25\\phantom{\\rule{0.28em}{0ex}}\\mathrm{GeV}$ is presented. The data reveal two narrow structures at ${E}_{\\ensuremath{\\gamma}}=1.036$ and ${E}_{\\ensuremath{\\gamma}}=1.119 \\mathrm{GeV}$. They may signal narrow resonances with masses near 1.68 and $1.72\\phantom{\\rule{0.28em}{0ex}}\\mathrm{GeV}$, or they may be generated by the sub-threshold $K\\ensuremath{\\Lambda}$ and $\\ensuremath{\\omega}p$ production. Their decisive identification requires additional theoretical and experimental efforts.