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dc.contributor.advisorAron Bernstein.en_US
dc.contributor.authorStave, Sean C. (Sean Christoph), 1976-en_US
dc.contributor.otherMassachusetts Institute of Technology. Dept. of Physics.en_US
dc.date.accessioned2007-05-16T15:22:52Z
dc.date.available2007-05-16T15:22:52Z
dc.date.copyright2006en_US
dc.date.issued2006en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/37213
dc.descriptionThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.en_US
dc.descriptionThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.en_US
dc.descriptionIn title on t.p., "[gamma]" appears as the lower-case Greek letter; "[right arrow]" appears as the symbol; and, "[Delta]" appears as the upper-case Greek letter. Vita.en_US
dc.descriptionIncludes bibliographical references (p. 213-220).en_US
dc.description.abstractThe 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.en_US
dc.description.abstract(cont.) This work reports results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios obtained from fitting the new data with models using a three parameter, resonant multipole fit: M3/2 = (40.33 i 0.63stat+syst ± 0.61model) (10-3/m,r+), E2/M1 = Re(E3/2/M3/2) = (-2.28 i 0.29stat+syst ± 0.20modeI)%, and C2/M1 = Re(S3/M+3/2) = (-4.81 ± 0.27stat+syst i 0.26model)%. These new results for the transition multi-poles disagree with predictions of the quark models but are in reasonable agreement with a chiral extrapolation of lattice QCD, chiral effective field theory and dynamical model results confirming the dominance and general Q2 variation of the long range pionic contribution. While there is qualitative agreement with the models, there is no quantitative agreement thus indicating the need for further improvement of the models.en_US
dc.description.statementofresponsibilityby Sean C. Stave.en_US
dc.format.extent223 p.en_US
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.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.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582
dc.subjectPhysics.en_US
dc.titleLowest Q² measurement of the [gamma] *p [right arrow] [Delta] reaction : probing the pionic contributionen_US
dc.typeThesisen_US
dc.description.degreePh.D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Dept. of Physics.en_US
dc.identifier.oclc82142896en_US


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