Phys. Rev. Lett.
99,
202002
(2007)
[5 pages]
Measurements of the Proton Elastic-Form-Factor Ratio μpGEp/GMp at Low Momentum Transfer
G. Ron et al. Jefferson Lab Hall A Collaboration
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G. Ron1, J. Glister2,3, B. Lee4, K. Allada5, W. Armstrong6, J. Arrington7, A. Beck8, F. Benmokhtar9, B. L. Berman10, W. Boeglin11, E. Brash12, A. Camsonne13, J. Calarco14, J. P. Chen13, Seonho Choi4, E. Chudakov13, L. Coman15, B. Craver15, F. Cusanno16, J. Dumas17, C. Dutta5, R. Feuerbach13, A. Freyberger13, S. Frullani16, F. Garibaldi16, R. Gilman13,17, O. Hansen13, D. W. Higinbotham13, T. Holmstrom18, C. E. Hyde19,20, H. Ibrahim19, Y. Ilieva10, C. W. de Jager13, X. Jiang17, M. K. Jones13, H. Kang4, A. Kelleher18, E. Khrosinkova21, E. Kuchina17, G. Kumbartzki17, J. J. LeRose13, R. Lindgren15, P. Markowitz11, S. May-Tal Beck8, E. McCullough2, D. Meekins13, M. Meziane18, Z.-E. Meziani6, R. Michaels13, B. Moffit18, B. E. Norum15, Y. Oh4, M. Olson22, M. Paolone23, K. Paschke15, C. F. Perdrisat18, E. Piasetzky1, M. Potokar24, R. Pomatsalyuk13,25, I. Pomerantz1, A. Puckett26, V. Punjabi27, X. Qian28, Y. Qiang26, R. Ransome17, M. Reyhan17, J. Roche29, Y. Rousseau17, A. Saha13, A. J. Sarty2, B. Sawatzky15,6, E. Schulte17, M. Shabestari15, A. Shahinyan30, R. Shneor1, S. Širca24,31, K. Slifer15, P. Solvignon7, J. Song4, R. Sparks13, R. Subedi21, S. Strauch23, G. M. Urciuoli32, K. Wang15, B. Wojtsekhowski13, X. Yan4, H. Yao6, X. Zhan26, and X. Zhu28 (Jefferson Lab Hall A Collaboration)
1Tel Aviv University, Tel Aviv 69978, Israel
2Saint Mary’s University, Halifax, Nova Scotia B3H 3C3, Canada
3Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada
4Seoul National University, Seoul 151-747, Korea
5University of Kentucky, Lexington, Kentucky 40506, USA
6Temple University, Philadelphia, Pennsylvania 19122, USA
7Argonne National Laboratory, Argonne, Illinois 60439, USA
8NRCN, Beer-Sheva 84190, Israel
9University of Maryland, Baltimore, Maryland 20742, USA
10George Washington University, Washington, D.C. 20052, USA
11Florida International University, Miami, Florida 33199, USA
12Christopher Newport University, Newport News, Virginia, 23606, USA
13Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA
14University of New Hampshire, Durham, New Hampshire 03824, USA
15University of Virginia, Charlottesville, Virginia 22904, USA
16INFN, Sezione Sanitá and Istituto Superiore di Sanitá, Laboratorio di Fisica, I-00161 Rome, Italy
17Rutgers, The State University of New Jersey, Piscataway, New Jersey 08855, USA
18College of William and Mary, Williamsburg, Virginia 23187, USA
19Old Dominion University, Norfolk, Virginia 23508, USA
20Université Blaise Pascal/CNRS-IN2P3, F-63177 Aubière, France
21Kent State University, Kent, Ohio 44242, USA
22Saint Norbert College, Green Bay, Wisconsin 54115, USA
23University of South Carolina, Columbia, South Carolina 29208, USA
24Institute “Jožef Stefan”, 1000 Ljubljana, Slovenia
25Kharkov Institute, Kharkov 310108, Ukraine
26Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
27Norfolk State University, Norfolk, Virginia 23504, USA
28Duke University, Durham, North Carolina 27708, USA
29Ohio University, Athens, Ohio 45701, USA
30Yerevan Physics Institute, Yerevan 375036, Armenia
31Department of Physics, University of Ljubljana, 1000 Ljubljana, Slovenia
32INFN, Sezione di Roma, 00185 Roma, Italy
Received 4 June 2007; published 13 November 2007
High-precision measurements of the proton elastic form-factor ratio, μpGEp/GMp, have been made at four-momentum transfer, Q2, values between 0.2 and 0.5 GeV2. The new data, while consistent with previous results, clearly show a ratio less than unity and significant differences from the central values of several recent phenomenological fits. By combining the new form-factor ratio data with an existing cross-section measurement, one finds that in this Q2 range the deviation from unity is primarily due to GEp being smaller than expected.
© 2007 The American Physical Society
URL:
http://link.aps.org/doi/10.1103/PhysRevLett.99.202002
DOI:
10.1103/PhysRevLett.99.202002
PACS:
14.20.Dh, 13.40.Gp, 24.70.+s, 25.30.Bf
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