Design of high-light-collection-efficiency optical fiber for germanium detectors immersed in liquid argon

Abstract The implementation of Slicon Photon-Multipliers (SiPMs) wave-length shifting (WLS) fibers light response system in liquid argon (LAr) is a promising technology for suppressing background in rare event experiments. Moreover, it is particularly relevant for experiments that utilize high-purity germanium (HPGe) detectors directly operated in LAr, such as the direct detection of dark matter and neutrinoless double beta decay. In this work, we exhibit a designed WLS fiber for the LAr detector, verify the feasibility of the manufacturing technology, and simulation research about its light collection performance. The novel fiber incorporates two materials, styrene and 1,1,4,4-tetraphenyl-1,3-butadiene (TPB). The pre-experiments proved that the fiber has good WLS and light-conducting properties for ultraviolet light. In addition, the effect of different light collection methods on detection efficiency was assessed by Geant4 simulation. Our results show that adding optical fibers can significantly increase light collection efficiency. Compared with the design of TPB coating with commercial fiber, the new structure of WLS fiber can improve the light collection efficiency by 50%. The simulation results indicate that the new fiber structure can enhance the light collection efficiency of the LAr detection system, thereby improving the anti-coincidence system's performance in rare event experiments.