First measurement of the helicity asymmetry E in η photoproduction on the proton.

Document Type


Publication Date



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.


© 2016 The Author(s)

Published by Elsevier B.V. under CC License Attribution 4.0 International (CC BY 4.0)

Publication Title

Physics Letters B

Published Citation

Senderovich, Igor, Brian T. Morrison, M. Dugger, Barry G. Ritchie, E. Pasyuk, R. Tucker, J. Brock, Biselli A. et al [CLAS Collaboration]. "First measurement of the helicity asymmetry E in η photoproduction on the proton." Physics Letters B 755 (2016): 64-69. https://doi.org/10.1016/j.physletb.2016.01.044