Speaker
Mikhail Yurov
(UVA)
Description
Two experimental techniques, Rosenbluth separation and recoil polarization transfer, used to extract proton's electromagnetic form factors ratio $\frac{G_E}{G_M}$ yield markedly different results. Modern theoretical calculations suggest that two-photon exchange (TPE) might be responsible for the observed discrepancy and that it is $\varepsilon$ dependent. Jefferson Lab Experiment E05-017 was designed to measure the TPE contribution over a wide range of $\varepsilon$ and $Q^2$. In contrast with the conventional Rosenbluth method, E05-017 detected the elastically scattered proton rather
than the electron. At a fixed $Q^{2}$, proton momentum is constant for all $\varepsilon$ while the proton rate and the radiation corrections have a smaller dependence on $\varepsilon$ compared to ($e,e{\textprime}$) detection. This allows a much more precise extraction of the form factor ratios. This approach can be exploited to significantly improve precision for experiments comparing $e^{+}p$ and $e^{-}p$ scattering which have been used to directly constrain TPE at lower $Q^2$. Positron production development at JLab in the context of the 12 GeV program opens up an opportunity to directly explore TPE effects at low $\varepsilon$ and much higher values of momentum transfer where the disagreement between the Rosenbluth separation and polarization transfer methods is largest. The current status of E05-017 analysis along with preliminary results will be presented. The kinematic coverage and the effects on TPE extraction that could be obtained from measurements with a 5uA positron beam combined with proton detection will be outlined.
Primary author
Mikhail Yurov
(UVA)
