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Jefferson Lab experiment E08-007 measured the proton elastic form factorratio $\mu_pG_E/G_M$ in the range of $Q^2=0.3-0.7(\mathrm{GeV}/c)^2$ by recoilpolarimetry. Data were taken in 2008 at the Thomas Jefferson NationalAccelerator Facility in Virginia, USA. A 1.2 GeV polarized electron beam wasscattered off a cryogenic hydrogen target. The recoil proton was detected inthe left HRS in coincidence with the elasticly scattered electrons tagged bythe BigBite spectrometer. The proton polarization was measured by the focalplane polarimeter (FPP). In this low $Q^2$ region, previous measurement fromJefferson Lab Hall A (LEDEX) along with various fits and calculations indicatesubstantial deviations of the ratio from unity. For this new measurement, theproposed statistical uncertainty ($<1%$) was achieved. These new results are afew percent lower than expected from previous world data and fits, whichindicate a smaller $G_{Ep}$ at this region. Beyond the intrinsic interest innucleon structure, the new results also have implications in determining theproton Zemach radius and the strangeness form factors from parity violationexperiments.

High Precision Measurement of the Proton Elastic Form Factor Ratio at Low $Q^2$