The ratio of the electric and magnetic form factor of the proton, \(\mu_p G_E^p/G_M^p\), has been measured for elastic electron-proton scattering with polarized beam and target up to four-momentum ...transfer squared, \(Q^2=5.66\) (GeV/c)\(^2\) using the double spin asymmetry for target spin orientation aligned nearly perpendicular to the beam momentum direction. This measurement of \(\mu_p G_E^p/G_M^p\) agrees with the \(Q^2\) dependence of previous recoil polarization data and reconfirms the discrepancy at high \(Q^2\) between the Rosenbluth and the polarization-transfer method with a different measurement technique and systematic uncertainties uncorrelated to those of the recoil-polarization measurements. The form factor ratio at \(Q^2\)=2.06 (GeV/c)\(^2\) has been measured as \(\mu_p G_E^p/G_M^p = 0.720 \pm 0.176_{stat} \pm 0.039_{sys}\), which is in agreement with an earlier measurement with the polarized target technique at similar kinematics. The form factor ratio at \(Q^2\)=5.66 (GeV/c)\(^2\) has been determined as \(\mu_p G_E^p/G_M^p=0.244\pm0.353_{stat}\pm0.013_{sys}\), which represents the highest \(Q^2\) reach with the double spin asymmetry with polarized target to date.
Cross sections for semi-inclusive electroproduction of charged pions (\(\pi^{\pm}\)) from both proton and deuteron targets were measured for \(0.2<x<0.5\), \(2<Q^2<4\) GeV\(^2\), \(0.3<z<1\), and ...\(P_t^2<0.2\) GeV\(^2\). For \(P_t<0.1\) GeV, we find the azimuthal dependence to be small, as expected theoretically. For both \(\pi^+\) and \(\pi^-\), the \(P_t\) dependence from the deuteron is found to be slightly weaker than from the proton. In the context of a simple model, this implies that the initial transverse momenta width of \(d\) quarks is larger than for \(u\) quarks and, contrary to expectations, the transverse momentum width of the favored fragmentation function is larger than the unfavored one.
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