Calibration of the Nab Silicon Detectors with a Radioactive Source Insertion System

The Nab experiment at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) aims to test the Standard Model through measurements of free neutron beta decay parameters, specifically the electron-antineutrino correlation coefficient and the Fierz Interference term. The Nab spectrometer will detect energy and momentum of betas and protons with a magnet system and a pair of highly segmented silicon detectors. To characterize the response of the silicon detectors and to constrain systematic effects stemming from electron energy reconstruction, the Radioactive Source Insertion System (RSIS) has been designed, fabricated, and installed to the Nab spectrometer in previous years. The RSIS functions to introduce calibration sources on ultrathin films into the cryogenic bore of the Nab spectrometer’s superconducting magnet system, and perform 2D scans across the decay volume, where the magnetic field carries the charged particles to the silicon detectors.

In this talk, I will present results from the recent operation of the RSIS in tandem with the silicon detector, highlights of recent upgrades to the system for improved operational capability, an outlook for the upcoming calibration campaign, and a comparison to Monte Carlo simulation of the experimental geometry.