6533b7cffe1ef96bd1258ca2

RESEARCH PRODUCT

Search for Effects Beyond the Born Approximation in Polarization Transfer Observables ine→pElastic Scattering

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Intensive theoretical and experimental efforts over the past decade have aimed at explaining the discrepancy between data for the proton electric to magnetic form factor ratio, $$G_{E}/G_{M}$$, obtained separately from cross section and polarization transfer measurements. One possible explanation for this difference is a two-photon-exchange (TPEX) contribution. In an effort to search for effects beyond the one-photon-exchange or Born approximation, we report measurements of polarization transfer observables in the elastic $$H(\vec{e},e'\vec{p})$$ reaction for three different beam energies at a fixed squared momentum transfer $Q^2 = 2.5$ GeV$^2$, spanning a wide range of the virtual photon polarization parameter, $$\epsilon$$. From these measured polarization observables, we have obtained separately the ratio $R$, which equals $$\mu_p G_{E}/G_{M}$$ in the Born approximation, and the longitudinal polarization transfer component $$P_\ell$$, with statistical and systematic uncertainties of $$\Delta R \approx \pm 0.01 \mbox{(stat)} \pm 0.013 \mbox{(syst)}$$ and $$\Delta P_\ell/P^{Born}_{\ell} \approx \pm 0.006 \mbox{(stat)}\pm 0.01 \mbox{(syst)}$$. The ratio $R$ is found to be independent of $$\epsilon$$ at the 1.5% level, while the $$\epsilon$$ dependence of $$P_\ell$$ shows an enhancement of $$(2.3 \pm 0.6) %$$ relative to the Born approximation at large $$\epsilon$$.