Experimental study of $\eta$ meson photoproduction reaction at MAMI

Abstract

New data for the differential cross sections, polarization observables $T$, $F$, and $E$ in the reaction of $\eta$ photoproduction on proton from the threshold up to a center-of-mass energy of W=1.9 GeV are presented. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. The polarization measurements were made using a frozen-spin butanol target and circularly polarized photon beam. The results are compared to existing experimental data and different PWA predictions. The data solve a long-standing problem related the angular dependence of older $T$ data close to threshold. The unexpected relative phase motion between $s$- and $d$-wave amplitudes required by the old data is not confirmed. At higher energies, all model predictions fail to reproduce the new polarization data indicating a significant impact on our understanding of the underlying dynamics of $\eta$ meson photoproduction. Furthermore, we present a fit of the new data and existing data from GRAAL for $\Sigma$ asymmetry based on an expansion in terms of associated Legendre polynomials. A Legendre decomposition shows the sensitivity to small partial-wave contributions. The sensitivity of the Legendre coefficients to the nucleon resonance parameters is shown using the $\eta$MAID isobar model.

8 pages, 13 figures. International Conference Dark Matter, Hadron Physics and Fussion Physics, Messina (Italy), Sept- 24-26. 2014

References in corpus (4)

• Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C
• Study of the gp-->etap reaction with the Crystal Ball detector at the Mainz Microtron(MAMI-C)
• Measurement of the transverse target and beam-target asymmetries in $\eta$ meson photoproduction at MAMI
• Energy dependent analysis of eta-meson photoproduction on protons and neutrons without background in the energy region up to 3.4 GeV

Cited by in corpus (1)

• Ordinary and exotic mesons in the extended Linear Sigma Model