Determination of Z coordinate from track width in MiniTPC

A gas-filled Time Projection Chamber and a radioactive neutron source were used to study recoil tracks produced by scattering of the multi-MeV neutrons on gas nuclei. Since the event readout is triggered by the first electron arrival, the initial time and position in the electron drift direction are unknown, leading to a translational uncertainty in this direction. By using the track width due to electron diffusion, the coordinate along the drift direction was determined. With a suitable width calibration at a known drift distance, it is found that width measurements of the track can provide useful information for establishing a well-defined gas fiducial volume for the interactions. The coordinate determination is also sufficiently precise that it can be used as a third parameter in kinematic reconstruction of the neutron collision, providing improved knowledge of the neutron collision process. Despite a wide range of track ionization levels resulting from the broad spectrum of neutron energies and varying angles of scatter, the coordinate determination is not sensitive to the track ionization.