An APD for the efficient detection of the fast scintillation component of BaF 2

Barium fluoride crystals are the baseline choice for the calorimeter of the Mu2e experiment at Fermilab. By the fast (decay time 0.9ns) 220nm scintillation component and discriminating against the larger slow (decay time 630ns) 300nm component, it is possible to build a radiation-hard calorimeter with good energy and time resolution and high rate capability. This requires a solid state photosensor with high quantum efficiency at 220nm, discrimination against the 300nm component and good rise and decay times. Progress on the development of such a sensor is presented.