High Precision Measurement of the Proton Elastic Form Factor Ratio $\mu_pG_E/G_M$ at low $Q^2$
Abstract
We report a new, high-precision measurement of the proton elastic form factor ratio \mu_p G_E/G_M for the four-momentum transfer squared Q^2 = 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 \mu_p G_E/G_M from unity observed in previous polarization measurements at high Q^2 continues down to the lowest Q^2 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 Q^2 range. We obtain new extractions of the proton electric and magnetic radii, which are <r^2_E>^(1/2)=0.875+/-0.010 fm and <r^2_M>^(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.
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Cite
@article{arxiv.1102.0318,
title = {High Precision Measurement of the Proton Elastic Form Factor Ratio $\mu_pG_E/G_M$ at low $Q^2$},
author = {X. Zhan and K. Allada and D. S. Armstrong and J. Arrington and W. Bertozzi and W. Boeglin and J. -P. Chen and K. Chirapatpimol and S. Choi and E. Chudakov and E. Cisbani and P. Decowski and C. Dutta and S. Frullani and E. Fuchey and F. Garibaldi and S. Gilad and R. Gilman and J. Glister and K. Hafidi and B. Hahn and J. -O. Hansen and D. W. Higinbotham and T. Holmstrom and R. J. Holt and J. Huang and G. M. Huber and F. Itard and C. W. de Jager and X. Jiang and J. Johnson and J. Katich and R. de Leo and J. J. LeRose and R. Lindgren and E. Long and D. J. Margaziotis and S. May-Tal Beck and D. Meekins and R. Michaels and B. Moffit and B. E. Norum and M. Olson and E. Piasetzky and I. Pomerantz and D. Protopopescu and X. Qian and Y. Qiang and A. Rakhman and R. D. Ransome and P. E. Reimer and J. Reinhold and S. Riordan and G. Ron and A. Saha and A. J. Sarty and B. Sawatzky and E. C. Schulte and M. Shabestari and A. Shahinyan and S. Sirca and P. Solvignon and N. F. Sparveris and S. Strauch and R. Subedi and V. Sulkosky and I. Vilardi and Y. Wang and B. Wojtsekhowski and Z. Ye and Y. Zhang},
journal= {arXiv preprint arXiv:1102.0318},
year = {2015}
}
Comments
12 pages, 3 figures