Evidence for narrow resonant structures at $W \approx 1.68$ and $W \approx 1.72$ GeV in real Compton scattering off the proton

TL;DR

This study reports the first measurement of beam asymmetry in real Compton scattering off the proton, revealing narrow structures at specific energies that could indicate new narrow resonances or threshold effects.

Contribution

It provides new experimental data on beam asymmetry in Compton scattering, highlighting potential narrow resonant structures near 1.68 and 1.72 GeV.

Findings

Two narrow structures observed at photon energies 1.036 and 1.119 GeV.

Structures may indicate narrow resonances or threshold effects.

Further research needed for definitive identification.

Abstract

First measurement of the beam asymmetry $\Sigma$ for Compton scattering off the proton in the energy range $E_{\gamma}=0.85 - 1.25$ GeV is presented. The data reveals two narrow structures at $E_{\gamma}= 1.036$ and $E_{\gamma}=1.119$ GeV. They may signal narrow resonances with masses near $1.68$ and $1.72$ GeV, or they may be generated by the sub-threshold $K\Lambda$ and $\omega p$ production. Their decisive identification requires additional theoretical and experimental efforts.