Extracting the Fifth Structure Function of the $\rm ^2H(e,e^\prime p)n$ Reaction

We have measured the imaginary part of the longitudinal-transverse interference term (the fifth structure function) of the $^2{\rm H}(e,e^\prime p)n$ reaction to test the hadronic model of nuclear physics. At Thomas Jefferson National Accelerator Facility, a 2.6-GeV electron beam was incident on a deuterium target. The beam polarization was rapidly and pseudo-randomly flipped parallel or anti-parallel to the beam momentum. Using a large-solid-angle, magnetic spectrometer, the CEBAF Large Acceptance Spectrometer (CLAS), we obtained two sets of data in the range $\rm Q^2=0.2-2.0 ~(GeV/c)^2$ using opposite polarizations of the toroidal magnetic field in CLAS. To extract the fifth structure function, we formed the helicity asymmetry $A^\prime_{LT}$. We start by taking the ratio of the difference of events for the two beam polarizations divided by their sum as a function of their missing momentum $p_m$ and $\phi_{pq}$, the out-of-plane angle between the scattering and reaction planes. The data in each $p_m$ bin were fitted as a function of $\phi_{pq}$ to a sinusoidal curve over the range $p_m = 0-0.7 ~ \rm GeV/c$. The amplitude of the fit is $A^\prime_{LT}$. The results were consistent with other methods for extracting $A^\prime_{LT}$.