Measurement of the transverse target and beam-target asymmetries in $\eta$ meson photoproduction at MAMI

Abstract

We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the $\vec{\gamma }\vec{p}\to \eta p$ reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of $\eta$ meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed.

Comments: 5 pages, 3 figures, accepted for publication in PRL