We report a new, high-precision measurement of the proton elastic form factor ratio μpGE/GM for the four-momentum transfer squared Q2=0.3-0.7(GeV/c)2. The measurement was performed at Jefferson Lab (JLab) in Hall A using recoil polarimetry. With a total uncertainty of approximately 1%, the new data clearly show that the deviation of the ratio μpGE/GM from unity observed in previous polarization measurements at high Q2 continues down to the lowest Q2 value of this measurement. The updated global fit that includes the new results yields an electric (magnetic) form factor roughly 2% smaller (1% larger) than the previous global fit in this Q2 range. We obtain new extractions of the proton electric and magnetic radii, which are 〈rE2v1/2=0.875±0.010 fm and 〈rM2〉1/2=0.867±0.020 fm. The charge radius is consistent with other recent extractions based on the electron-proton interaction, including the atomic hydrogen Lamb shift measurements, which suggests a missing correction in the comparison of measurements of the proton charge radius using electron probes and the recent extraction from the muonic hydrogen Lamb shift.
|Original language||American English|
|Number of pages||6|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - 3 Nov 2011|
Bibliographical noteFunding Information:
We thank the Jefferson Lab Physics and Accelerator Divisions. This work was supported by the National Science Foundation, the Department of Energy , including Contract No. DE-AC02-06CH11357 , and the US–Israeli Bi-National Scientific Foundation . Jefferson Science Associates operates the Thomas Jefferson National Accelerator Facility under DOE Contract No. DE-AC05-06OR23177 .