A solid insulating sphere of radius \(R\) carries a net charge \(Q\) distributed uniformly throughout its volume. The electric field energy density stored in space is defined by \(u = \dfrac{1}{2}\varepsilon_0 E^2\). Integrating this energy density over all space, which of the following expressions represents the total electrostatic potential energy \(U\) stored in the electric field of the sphere?