Object Tracking Vision System for Mapping the UCN$\tau$ Apparatus Volume.

The UCN$\tau$ collaboration has an immediate goal to measure the lifetime of the free neutron to within 0.1%, i.e. about 1~s. The UCN$\tau$ apparatus is a magneto-gravitational “bottle” system. This system holds low energy, or ultracold, neutrons in the apparatus with the constraint of gravity, and keeps these low energy neutrons from interacting with the bottle via a strong $\sim$1~T surface magnetic field created by a bowl-shaped array of permanent magnets. The apparatus is wrapped with energized coils to supply a magnetic field throughout the "bottle" volume to prevent depolarization of the neutrons. An object-tracking stereo-vision system will be presented that precisely tracks a Hall probe and allows a mapping of the magnetic field throughout the volume of the UCN$\tau$ bottle. The stereo-vision system utilizes two cameras and open source openCV software to track an object's 3-d position in space in real time. The desired resolution is $\pm$1~mm resolution along each axis. The vision system is being used as part of an even larger system to map the magnetic field of the UCN$\tau$ apparatus and expose any possible systematic effects due to field cancellation or low field points which could allow neutrons to depolarize and possibly escape from the apparatus undetected.