It is currently unknown if the neutron has an electric dipole moment, all the current experiments are consistent with zero and provide only an upper bound, meaning the electric dipole moment cannot exceed some value. It does have charged constituents, two down quarks and one up quark, so it's possible that it has a non-zero moment. Each down quark has a charge of
−1/3e
and the up quark has a charge of
+2/3e
. Imagine the two down quarks right next to each other and separated by some distance from the up quark, so that we we have a pure dipole. Now, we perform an experiment to measure the neutron dipole moment, and obtain a value consistent with zero and which cannot exceed
d=5.9E−26ecm
. What is the maximum possible separation between the up quark and the down quarks?
s=
m
. What is the ratio between this distance and the radius of the neutron
r=8.6E−16 m
?