Narrow Results

We present a preliminary analysis of the photon beam asymmetry observable (Σ) from the photoproduction reaction channel γn → π^-p. This new data was obtained using the near-4π CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory, USA, employing a linearly polarised photon beam with an energy range 1.1 - 2.3 GeV. The measurement will provide new data to address the poorly established neutron excitation spectrum and will greatly expand the sparse world data-set both in energy and angle.

The high-energy photoproduction of light-quark pseudoscalar and scalar mesons is an effective tool for understanding the properties of strong interaction in the nonperturbative regime. It has been investigated theoretically using Regge-cut phenomenology with massive quasi-particle exchange in the high-energy regime, and the linearly polarized photon beam asymmetry $\mathrm{\Sigma }$ can provide insight into the dominant production mechanism. In the low-energy region, it can provide constraints on ”background” to baryon resonance extraction. With an almost 50-year history, intensive experiments on meson photoproduction are growing vigorously at several international laboratories, such as JLab, ELSA, and MAMI. Recently the beam asymmetry $\mathrm{\Sigma }$ in high-energy ${\pi }^0/\eta$ photoproduction has been measured at GlueX, which is the first measurement both from the GlueX experiment and the 12 GeV upgraded JLab. The highest precision measurement of the ${\pi }^0$ asymmetry and the first measurement of $\eta$ beam asymmetry at a beam energy above 3 GeV are presented. A broad meson photoproduction project, including scalar meson $a_0(980)/f_0(980)$, is under way at GlueX. In the proceedings, we report the beam asymmetry results for ${\pi }^0/\eta$ photoproduction at GlueX, as well as preliminary results for scalar meson photoproduction in the ${\pi }^0{\pi }^0$ and ${\pi }^0\eta$ channels.

Recently, the CLAS collaboration at Thomas Jefferson Nation Acceleration Facility reported the total cross section data for K* photoproduction, and found that the t-channel K exchange dominates the production amplitudes at small scattering angles. The measurement of forward-angle beam spin asymmetries for this reaction, where the theoretical calculations show an unambiguous signal, would establish the role of the κ(800). We have measured the photon beam asymmetry for the γp → K*⁰Σ⁺ reaction on a Liquid Hydrogen target in the energy from threshold to 3.0 GeV by using a linearly polarized photon beam at SPring-8.