![](https://d3ilqtpdwi981i.cloudfront.net/seHjWGpKV6GOB0lT3htnNALOq-g=/425x550/smart/https://bepress-attached-resources.s3.amazonaws.com/uploads/b2/78/c3/b278c371-bae6-4a6a-bc60-93292990349c/thumbnail_ac67bd10-2612-46de-a14c-ab18973b1495.jpg)
Results are presented for the first measurement of the double-polarization helicity asymmetry E for the η photoproduction reaction . Data were obtained using the FROzen Spin Target (FROST) with the CLAS spectrometer in Hall B at Jefferson Lab, covering a range of center-of-mass energy W from threshold to 2.15 GeV and a large range in center-of-mass polar angle. As an initial application of these data, the results have been incorporated into the Jülich–Bonn model to examine the case for the existence of a narrow ⁎ resonance between 1.66 and 1.70 GeV. The addition of these data to the world database results in marked changes in the predictions for the E observable from that model. Further comparison with several theoretical approaches indicates these data will significantly enhance our understanding of nucleon resonances.
Available at: http://works.bepress.com/angela_biselli/128/
© 2016 The Author(s)
Published by Elsevier B.V. under CC License Attribution 4.0 International (CC BY 4.0)