Nucleon Form Factors

G.A. Miller

I was able to extend include the effects of the pion cloud[19] in our previous model[20,21]. This enabled a reasonably good description of all four nucleon electromagnetic form factors. I was also able to define and compute compute the matrix element of a spin-dependent density operator that enables one to characterize the shape of the proton[22]. The shapes range from spherical, to peanut to bagel, depending on the momentum and spin of the quarks. Some experimental consequences of these shapes are discussed.

Figure 4: Shapes of the proton. ${\bf s}$ is in the vertical direction $\bf\hat z$. Left column quark spin parallel to nucleon spin ${\bf n}=\hat{\bf s}$. Right column : quark spin anti-parallel to nucleon spin ${\bf n}=-{\bf s}$. The value of $K$ increases from 0 to 1 to 4 GeV/c.