Determination of the linear polarization of the Hall B tagged photon beam at JLab

The CLAS g9a experiment is part of the N* spectroscopy program at Jefferson Laboratory and has accumulated photoproduction data using a linearly polarized, tagged photon beam incident on a longitudinally polarized, frozen spin butanol target (FROST). Linearly polarized photons were produced via coherent bremsstrahlung from an electron beam incident on an oriented diamond crystal.\footnote{U. Timm, ``Coherent Bremsstrahlung of Electrons in Crystals.'' (1969), \textit{Fortschritte der Physik} \textbf{17}, 765-808.} The degree of polarization depends on the position of the coherent bremsstrahlung peak and at some settings, may exceed 90\%. The analysis of the spectrum shape was used to determine photon polarization. This report delineates the procedure and presents the results of these determinations.