First Measurement of the $\hat{I}\pounds$ Beam Asymmetry in $\hat{I}{\cdot }^{\prime }$ Photoproduction off the Proton near Threshold

Abstract

The $\hat{I}\pounds$ beam asymmetry in $\hat{I}{\cdot }^{\prime }$ photoproduction off the proton was measured at the GrAAL polarised photon beam with incoming photon energies of 1.461 and 1.480 GeV. For both energies the asymmetry as a function of the meson production angle shows a clear structure, more pronounced at the lowest one, with a change of sign around 90${}^o$. The observed behaviour is compatible with P-wave D-wave (or S-wave F-wave) interference, the closer to threshold the stronger. The results are compared to the existing state-of-the-art calculations that fail to account for the data.

6 pages, 4 figures, accepted for publication on Eur. Phys. J A