The $u$- and $d$-quark contributions to the elastic nucleon electromagnetic form factors have been determined by using experimental data on $G_E^n$, $G_M^n$, $G_E^p$, and $G_M^p$. Such a flavor separation of the form factors became possible up to negative four-momentum transfer squared $Q^2=3.4{\mathrm{GeV}}^2$ with recent data on $G_E^n$ from Hall A at Jefferson Lab. For $Q^2$ above $1{\mathrm{GeV}}^2$, for both the $u$ and the $d$ quark, the ratio of the Pauli and Dirac form factors, $F_2/F_1$, was found to be almost constant in sharp contrast to the behavior of $F_2/F_1$ for the proton as a whole. Also, again for $Q^2>1{\mathrm{GeV}}^2$, both $F_2^d$ and $F_1^d$ are roughly proportional to $1/Q^4$, whereas the dropoff of $F_2^u$ and $F_1^u$ is more gradual.

• Received 8 March 2011

DOI:https://doi.org/10.1103/PhysRevLett.106.252003