Speaker
Description
The exploration of nucleon structure and electromagnetic transitions from ground state to excited state is a cornerstone of nuclear physics research. Meson electro-production experiments have opened new avenues for investigating these phenomena, particularly in the 12 GeV era at Jefferson Lab with the CLAS12 spectrometer. The $\eta N$ final states, accessible only through isospin $I = 1/2$ resonances, provide a unique tool for studying nucleon excitations. By simplifying the analysis and enabling a cleaner extraction of resonance properties compared to the extensively studied $\pi N$ final states, $\eta$ electro-production offers a complementary approach to unraveling the structure of excited nucleons. This work presents the first-ever measurement of the beam spin asymmetry (BSA) in exclusive $\eta$ electro-production, covering a previously unexplored kinematic region with $1.6 \leq W \leq 2.2$~GeV. The BSA is extracted from the CLAS12 data using a comprehensive analysis framework that carefully considers the statistical limitations of the data set. The results are compared to predictions from theoretical models, such as the J"{u}lich-Bonn-Washington (JBW) and MAID, as well as compared to previously published cross-section and spin observable results from CLAS, and SLAC. Notably, the extracted BSA exhibits discrepancies with the model predictions, highlighting the potential for refining theoretical descriptions of nucleon resonances and their electromagnetic couplings through the incorporation of these new data. The high-precision data obtained in this previously unmeasured kinematic region now serve as valuable input for refining models.
