Testing the electronics for the Nab Experiment at SNS

The Nab experiment at the SNS is designed to measure the values of the beta neutrino correlation and Fierz interference terms in neutron β-decay using a cold neutron beam.  These two parameters provide critical input for tests of the standard model of particle physics which probe for new physics at energy scales higher (in some scenarios) than those achievable at the Large Hadron Collider.  To make these measurements we have developed 1.5-2 mm thick silicon detectors with ~11.5 cm diameter active regions divided into 127 hexagonal pixels operated as reverse-biased diodes.  A Field Effect Transistor (FET) front end and two stages of amplification convert the integrated charge into energies of incoming particles into voltage signals read into the Data Acquisition System (DAQ).  A new circuit was designed to simulate pulses from charged particles to characterize the performance of the electronics.  Using this with the DAQ sped up the testing process by a factor of 30 from a benchtop setup.  Initial results provide a range in which the response signal is directly proportional to the incoming particle’s energy, and reveals at what point the FETs become saturated.