Observation of the $p{\eta }^{\prime }$ Cusp in the New Precise Beam Asymmetry $\Sigma$ Data for $\gamma p\to p\eta$

Abstract

Data on the beam asymmetry $\Sigma$ in the photoproduction of $\eta$ mesons off protons are reported for tagged photon energies from 1130 to 1790 MeV (mass range from $W=$ 1748 MeV to $W=$ 2045 MeV). The data cover the full solid angle that allows for a precise moment analysis. For the first time, a strong cusp effect in a polarization observable has been observed that is an effect of a branch-point singularity at the $p{\eta }^{\prime }$ threshold [$E_{\gamma }=$ 1447 MeV ($W=$ 1896 MeV)]. The latest BnGa partial wave analysis includes the new beam asymmetry data and yields a strong indication for the $N(1895){\frac{1}{2}}^{-}$ nucleon resonance, demonstrating the importance of including all singularities for a correct determination of partial waves and resonance parameters.

References in corpus (6)

• Chiral dynamics of the S11(1535) and S11(1650) resonances revisited
• Measurement of eta photoproduction on the proton from threshold to 1500 MeV
• Eta photoproduction in a combined analysis of pion- and photon-induced reactions
• Linearly polarised photon beams at ELSA and measurement of the beam asymmetry in pi^0-photoproduction off the proton
• Relevance of complex branch points for partial wave analysis
• Measurement of the Helicity Asymmetry $E$ for the reaction $\gamma p\to {\pi }^{0}p$

Cited by in corpus (6)

• 50 Years of Quantum Chromodynamics
• Light Baryon Spectroscopy
• Light baryon resonances from a coupled-channel study including $\mathbf{K\Sigma }$ photoproduction
• Differential cross sections and photon beam asymmetries of $\eta$ photoproduction on the proton at $E_{\gamma }$ = 1.3-2.4 GeV
• Spectral function of the ${\eta }^{\prime }$ meson in nuclear medium based on phenomenological models
• New graphical criterion for the selection of complete sets of polarization observables and its application to single-meson photoproduction as well as electroproduction