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Precise measurements of the proton electromagnetic form factor ratio $R =\mu_p G_E^p/G_M^p$ using the polarization transfer method at Jefferson Lab haverevolutionized the understanding of nucleon structure by revealing the strongdecrease of $R$ with momentum transfer $Q^2$ for $Q^2 \gtrsim 1$ GeV$^2$, instrong disagreement with previous extractions of $R$ from cross sectionmeasurements. In particular, the polarization transfer results have exposed thelimits of applicability of the one-photon-exchange approximation andhighlighted the role of quark orbital angular momentum in the nucleonstructure. The GEp-II experiment in Jefferson Lab's Hall A measured $R$ at four$Q^2$ values in the range 3.5 GeV$^2 \le Q^2 \le 5.6$ GeV$^2$. A possiblediscrepancy between the originally published GEp-II results and more recentmeasurements at higher $Q^2$ motivated a new analysis of the GEp-II data. Thisarticle presents the final results of the GEp-II experiment, including detailsof the new analysis, an expanded description of the apparatus and an overviewof theoretical progress since the original publication. The key result of thefinal analysis is a systematic increase in the results for $R$, improving theconsistency of the polarization transfer data in the high-$Q^2$ region. Thisincrease is the result of an improved selection of elastic events which largelyremoves the systematic effect of the inelastic contamination, underestimated bythe original analysis.

Final Analysis of Proton Form Factor Ratio Data at $\mathbf{Q^2 = 4.0}$, 4.8 and 5.6 GeV$\mathbf{^2}$