Phys. Rev. Lett.
88,
122001
(2002)
[5 pages]
Q2 Dependence of Quadrupole Strength in the γ*p → Δ+(1232) → pπ0 Transition
K. Joo et al. (The CLAS Collaboration)
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K. Joo1, L. C. Smith1, V. D. Burkert3, R. Minehart1, I. G. Aznauryan4, L. Elouadrhiri2,3, S. Stepanyan4,23, G. S. Adams24, M. J. Amaryan4, E. Anciant26, M. Anghinolfi15, D. S. Armstrong8, B. Asavapibhop29, G. Audit26, T. Auger26, H. Avakian14, S. Barrow12, H. Bagdasaryan4, M. Battaglieri15, K. Beard18, M. Bektasoglu23, W. Bertozzi20, N. Bianchi14, A. S. Biselli24, S. Boiarinov16, B. E. Bonner25, W. K. Brooks3, J. R. Calarco30, G. P. Capitani14, D. S. Carman22, B. Carnahan7, P. L. Cole34, A. Coleman8, D. Cords3, P. Corvisiero15, D. Crabb1, H. Crannell7, J. Cummings24, E. De Sanctis14, R. De Vita15, P. V. Degtyarenko3, R. A. Demirchyan4, H. Denizli31, L. C. Dennis12, A. Deppman14, K. V. Dharmawardane23, K. S. Dhuga13, C. Djalali33, G. E. Dodge23, D. Doughty2,3, P. Dragovitsch12, M. Dugger5, S. Dytman31, M. Eckhause8, Y. V. Efremenko16, H. Egiyan8, K. S. Egiyan4, L. Farhi26, R. J. Feuerbach6, J. Ficenec35, K. Fissum20, T. A. Forest23, H. Funsten8, M. Gai28, V. B. Gavrilov16, S. Gilad20, G. P. Gilfoyle32, K. L. Giovanetti18, P. Girard33, K. A. Griffioen8, M. Guidal17, M. Guillo33, V. Gyurjyan3, D. Hancock8, J. Hardie2, D. Heddle2,3, J. Heisenberg30, F. W. Hersman30, K. Hicks22, R. S. Hicks29, M. Holtrop30, C. E. Hyde-Wright23, M. M. Ito3, D. Jenkins35, J. H. Kelley9, M. Khandaker21,3, K. Y. Kim31, W. Kim19, A. Klein23, F. J. Klein3, M. Klusman24, M. Kossov16, Y. Kuang8, S. E. Kuhn23, J. M. Laget26, D. Lawrence29, A. Longhi7, K. Loukachine35, M. Lucas33, R. W. Major32, J. J. Manak3, C. Marchand26, S. K. Matthews7, S. McAleer12, J. W. C. McNabb6, B. A. Mecking3, M. D. Mestayer3, C. A. Meyer6, M. Mirazita14, R. Miskimen29, V. Muccifora14, J. Mueller31, G. S. Mutchler25, J. Napolitano24, G. Niculescu22, B. Niczyporuk3, R. A. Niyazov23, M. S. Ohandjanyan4, A. Opper22, Y. Patois33, G. A. Peterson29, S. Philips13, N. Pivnyuk16, D. Pocanic1, O. Pogorelko16, E. Polli14, B. M. Preedom33, J. W. Price27, L. M. Qin23, B. A. Raue11,3, A. R. Reolon14, G. Riccardi12, G. Ricco15, M. Ripani15, B. G. Ritchie5, F. Ronchetti14, P. Rossi14, D. Rowntree20, P. D. Rubin32, C. W. Salgado21, M. Sanzone14, V. Sapunenko15, M. Sargsyan4, R. A. Schumacher6, Y. G. Sharabian4, J. Shaw29, S. M. Shuvalov16, A. Skabelin20, E. S. Smith3, T. Smith30, D. I. Sober7, M. Spraker9, P. Stoler24, M. Taiuti15, S. Taylor25, D. Tedeschi33, R. Thompson31, L. Todor6, T. Y. Tung8, M. F. Vineyard32, A. Vlassov16, H. Weller9, L. B. Weinstein23, R. Welsh8, D. P. Weygand3, S. Whisnant33, M. Witkowski24, E. Wolin3, A. Yegneswaran3, J. Yun23, Z. Zhou20, and J. Zhao20 (The CLAS Collaboration)
1University of Virginia, Department of Physics, Charlottesville, Virginia 22903
2Christopher Newport University, Newport News, Virginia 23606
3Thomas Jefferson National Accelerator Facility, 12000 Jefferson Avenue, Newport News, Virginia 23606
4Yerevan Physics Institute, 375036 Yerevan, Armenia
5Arizona State University, Department of Physics and Astronomy, Tempe, Arizona 85287
6Carnegie Mellon University, Department of Physics, Pittsburgh, Pennsylvania 15213
7Catholic University of America, Department of Physics, Washington D.C. 20064
8College of William and Mary, Department of Physics, Williamsburg, Virginia 23187
9Duke University, Physics Building TUNL, Durham, North Carolina 27706
10Department of Physics and Astronomy, Edinburgh University, Edinburgh EH9 3JZ, United Kingdom
11Florida International University, Miami, Florida 33199
12Florida State University, Department of Physics, Tallahassee, Florida 32306
13George Washington University, Department of Physics, Washington, D.C. 20052
14Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, P.O. 13, 00044 Frascati, Italy
15Instituto Nazionale di Fisica Nucleare, Sezione di Genova e Dipartimento di Fisica dell'Universita, 16146 Genova, Italy
16Institute of Theoretical and Experimental Physics, 25 B. Cheremushkinskaya, Moscow, 117259 Russia
17Institut de Physique Nucleaire d'Orsay, IN2P3, BP 1, 91406 Orsay, France
18James Madison University, Department of Physics, Harrisonburg, Virginia 22807
19Kyungpook National University, Department of Physics, Taegu 702-701, South Korea
20M.I.T.-Bates Linear Accelerator, Middleton, Massachusetts 01949
21Norfolk State University, Norfolk, Virginia 23504
22Ohio University, Department of Physics, Athens, Ohio 45701
23Old Dominion University, Department of Physics, Norfolk, Virginia 23529
24Rensselaer Polytechnic Institute, Department of Physics, Troy, New York 12181
25Rice University, Bonner Lab, Box 1892, Houston, Texas 77251
26CEA Saclay, DAPNIA-SPhN, F91191 Gif-sur-Yvette Cedex, France
27University of California at Los Angeles, Department of Physics and Astronomy, Los Angeles, California 90095-1547
28University of Connecticut, Physics Department, Storrs, Connecticut 06269
29University of Massachusetts, Department of Physics, Amherst, Massachusetts 01003
30University of New Hampshire, Department of Physics, Durham, New Hampshire 03824
31University of Pittsburgh, Department of Physics and Astronomy, Pittsburgh, Pennsylvania 15260
32University of Richmond, Department of Physics, Richmond, Virginia 23173
33University of South Carolina, Department of Physics, Columbia, South Carolina 29208
34University of Texas at El Paso, Department of Physics, El Paso, Texas 79968
35Virginia Polytechnic and State University, Department of Physics, Blacksburg, Virginia 24061
Received 2 October 2001; published 6 March 2002
Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q2 dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the γ*p→Δ+→pπ0 transition. We report new experimental values for the ratios E1+/M1+ and S1+/M1+ over the range Q2 = 0.4–1.8GeV2, extracted from precision p(e,e′p)π0 data using a truncated multipole expansion. Results are best described by recent unitary models in which the pion cloud plays a dominant role.
© 2002 The American Physical Society
URL:
http://link.aps.org/doi/10.1103/PhysRevLett.88.122001
DOI:
10.1103/PhysRevLett.88.122001
PACS:
13.60.Le, 13.40.Gp, 14.20.Gk
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