https://doi.org/10.1140/epja/i2002-10176-7
Original Paper
Deviation of the nucleon shape from spherical symmetry: Experimental status
Laboratory for Nuclear Science, MIT, MA 02139, Cambridge, USA
* e-mail: bernstein@mitlns.mit.edu
In this brief pedagogical overview the physical basis of the deviation of the nucleon shape from spherical symmetry will be presented along with the experimental methods used to determine it by the $\gamma^{*} p \rightarrow \Delta$ reaction. The fact that non-spherical electric (E2) and Coulomb quadrupole (C2) amplitudes have been observed will be demonstrated. We have measured these multipoles for the $N,\Delta$ system as a function of Q2 from the photon point through 4 GeV2 with modest precision. Their precise magnitude remains model dependent due to the contributions of the background amplitudes, although rapid progress is being made to reduce these uncertainties. A discussion of what is required to perform a model-independent analysis is presented. All of the data to date are consistent with an oblate shape for the proton and a prolate shape for the $\Delta$.
© Società Italiana di Fisica and Springer-Verlag, 2003
