Proton Detection System for the BL3 Experiment*

The BL3 experiment aims to measure the lifetime of the free neutron using the Sussex-ILL-NIST method to an uncertainty below 0.3 s.  Protons from in-flight decays of cold neutrons are trapped in a segmented electrode trap, which is “emptied” periodically and the protons guided to a detector via a magnetic field.  This approach requires absolute proton counting.  To reach the improved precision necessary for Standard Model tests with this approach requires a large area, segmented proton detector.  The design of the system will be discussed as well as the program of measurements to understand and characterize potential proton loss mechanisms.