R. Hasty,1
A.
M. Hawthorne-Allen,5
T. Averett,9
D. Barkhuff,4
D. H. Beck,1
E. J. Beise,3*
A. Blake,2
H. Breuer,3
R. Carr,2
S. Covrig,2
A. Danagoulian,1
G. Dodson,4
K. Dow,4
M. Farkhondeh,4
B. W. Filippone,2
J. Gao,2
M. C. Herda,3
T. M. Ito,2
C. E. Jones,2
W. Korsch,6
K. Kramer,9
S. Kowalski,4
P. Lee,2
R. D. McKeown,2
B. Mueller,7
M. Pitt,5
J. Ritter,5
J. Roche,9
V. Savu,2
D. T. Spayde,3
R. Tieulent,3
E. Tsentalovich,4
S. P. Wells,8
B. Yang,4
T. Zwart4
The violation of mirror symmetry in the weak force
provides a powerful tool to study the internal structure of the proton. Experimental results have been obtained that address the role of
strange quarks in generating nuclear magnetism. The measurement reported here provides an unambiguous constraint on strange quark contributions to the proton's magnetic moment through the
electron-proton weak interaction. We also report evidence for the
existence of a parity-violating electromagnetic effect known as the
anapole moment of the proton. The proton's anapole moment is not yet
well understood theoretically, but it could have important implications for precision weak interaction studies in atomic systems such as
cesium.
1 Department of Physics, University of Illinois
at Urbana-Champaign, Urbana, IL 61801, USA.
2 Kellogg Radiation Laboratory, California Institute
of Technology, Pasadena, CA 91125, USA.
3 Department
of Physics, University of Maryland, College Park, MD 20742, USA.
4 Bates Linear Accelerator Center, Laboratory for
Nuclear Science and Department of Physics, Massachusetts Institute of
Technology, Cambridge, MA 02139, USA.
5 Department
of Physics, Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061-0435, USA.
6 Department of
Physics and Astronomy, University of Kentucky, Lexington, KY 40506, USA.
7 Physics Division, Argonne National
Laboratory, Argonne, IL 60439, USA.
8 Department of
Physics, Louisiana Tech University, Ruston, LA 71272, USA.
9 Department of Physics, College of William and
Mary, Williamsburg, VA 23187, USA.
*
To whom correspondence should be addressed. E-mail:
beise{at}physics.umd.edu
