Beam Line Parameters for PERC at the ESS

Precision measurements of correlations in neutron beta decay test the standard model of particle physics. Here, pulsed neutron beams are invaluable to fight systematic effects. We show that the Proton Electron Radiation Channel PERC in pulsed mode is particularly well suited for a long-pulse spallation source, due to its long decay volume. We indicate how the optimum beam line parameters to run PERC at the ESS can be derived and compare the performance with that at the most powerful continuous source, the reactor of the ILL.