Lowest Q² measurement of the [gamma] *p [right arrow] [Delta] reaction : probing the pionic contribution

The first excited state of the proton, the Delta, can be reached through a magnetic dipole spin flip of one of the quarks (M1) or through electric and Coulomb quadrupole terms (E2 and C2) which indicate a deviation from spherical symmetry. The quark models using the color hyperfine interaction underestimate the size of the quadrupole terms by more than an order of magnitude. Models using the pion cloud do a much better job of describing the data. This is expected due to the spontaneous breaking of chiral symmetry which leads to a cloud of virtual p wave pions which introduce the non-spherical amplitudes. The data presented in this work fill gaps in the low Q2, long distance region where the pion cloud is expected to dominate and to produce significant Q2 variation. The p(e, e'p)7r0 reaction was measured in the A region at Q2 = 0.060 (GeV/c)2, the lowest Q2 to date for pion electroproduction, utilizing out-of-plane magnetic spectrometers at the Mainz Microtron in Germany.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2006

Author dc:creator

• Stave, Sean C. (Sean Christoph), 1976-

Advisor dc:contributor.advisor

• Aron Bernstein.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/37213

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/37213