Reconstructing nuclear recoil tracks in the Dark Matter Time Projection Chamber

Abstract

Astrophysical evidence indicates that 23% of our universe's energy density is in the form of nonluminous, nonbaryonic matter referred to as dark matter. One theoretically appealing dark matter candidate is the Weakly Interacting Massive Particle (WIMP). Because of astrophysical dynamics, the detectable signal from the expected WIMP dark matter halo should exhibit a unique daily directional modulation for which experiments can search . The Dark Matter Time Projection Chamber (DMTPC) group aims to provide an unequivocal detection of WIMP particles through the anisotropy in the angular recoil spectrum. DMTPC uses a low-pressure time projection chamber filled with CF 4 gas to search for WIMPs via elastic collisions. Crucial to this experiment is the fidelity of nuclear recoil track reconstruction. By extracting parameters such as the angle and vector direction of nuclear recoils, DMTPC has sensitivity to the anisotropic WIMP signal. This thesis develops a new track reconstruction algorithm motivated by the physics of nuclear energy loss in a diffuse gas medium. The algorithm is applied to simulated nuclear recoils and is compared to the existing track reconstruction algorithm. The new fitting algorithm outperforms the old algorithm in determining vector direction of nuclear recoils for recoil energies between 20 and 300 keV. The algorithm shows little sensitivity to CCD read noise. The length reconstruction of the new algorithm, however, fails to outperform the old algorithm below 100 keV.