Neutron EDM Model Scale Model

We know that the neutron is electrically neutral to better than one part in 1021. But we also know that neutrons are made up electrically charged sub-units called quarks.   Furthermore we know that the neutron charge distribution has a radial dependence.   But as far as we know the charge distribution is spherically symmetric. A non-zero electric dipole moment would contradict that, it would mean that neutrons are not quite round. Imagine a neutron the size of the earth. At that scale the nEDM@SNS goal precision (dn < 3×10-28 e·cm) can be translated into a relative difference between the polar and equatorial diameters that is a mere tens of nanometers.

Another way to picture the scale of the neutron’s EDM

The goal sensitivity of the nEDM@SNS experiment corresponds to a length scale of 10-28 cm. That’s a 1 in the 28th decimal place. This figure tries to put that tiny number into perspective. Each object is 100,000 times smaller than the object to its left.