A particle of mass \(m\) is confined in the ground state of a one-dimensional box extending from \(x = -2L\) to \(x = +2L\). The wave function of the particle in this state is \(\psi = \psi_0 \cos\dfrac{\pi x}{4L}\), where \(\psi_0\) is a constant. The energy eigenvalue corresponding to this state is: