Investigation of wavelength shifting materials in an active helium target and detector calibrations

Abstract

The strong nuclear force, responsible for binding nucleons and nuclei together, has proved challenging for physicists to study experimentally. Asymptotic freedom allows the strong force to be studied and tested e↵ectively at high energies; however in medium to low energy regimes, it remains to be solved. To establish a deeper understanding of how particles behave at these energy scales, the A2 Collaboration in Mainz, Germany, studies nucleon polarizabilites, which are fundamental structure constants specific to each nucleon. While these polarizability values are well established for protons, results obtained for the neutron remain unsatisfactory. To gain access to the neutron, the A2 Collaboration is using various helium targets: the cryogenic liquid 4He target that had been employed already, and the planned Active Helium target, set to contain gaseous helium isotopes. One of the main motivations for using the active target is it allows for the collection of scintillation light, which may be used to reduce backgrounds. However, the silicon photomultipliers in the prototype active volume are unable to detect the vacuum ultraviolet light emitted by the helium gas, and thus a wavelength shifting material is required. The work of this thesis examines various materials of this sort, including Tetraphenyl Butadiene, which has shown promising initial results and necessitates further examination. This thesis also examines detector calibrations in the aforementioned liquid 4He experiment from June of 2019, which include time and analog to digital onversion, setting o↵set values, energy pedestals and energy gains. A brief discussion of the beginnings of polarizability extraction is also touched upon. i