Measurement of the neutron charge radius and the role of its constituents.

ABSTRACT

The neutron is a cornerstone in our depiction of the visible universe. Despite the neutron zero-net electric charge, the asymmetric distribution of the positively- (up) and negatively-charged (down) quarks, a result of the complex quark-gluon dynamics, lead to a negative value for its squared charge radius, [Formula see text]. The precise measurement of the neutron's charge radius thus emerges as an essential part of unraveling its structure. Here we report on a [Formula see text] measurement, based on the extraction of the neutron electric form factor, [Formula see text], at low four-momentum transfer squared (Q2) by exploiting the long known connection between the N → Δ quadrupole transitions and the neutron electric form factor. Our result, [Formula see text], addresses long standing unresolved discrepancies in the [Formula see text] determination. The dynamics of the strong nuclear force can be viewed through the precise picture of the neutron's constituent distributions that result into the non-zero [Formula see text] value.