Development of a liquid argon detector with high light collection efficiency using tetraphenyl butadiene and a silicon photomultiplier array

To increase the light collection efficiency of a liquid argon (LAr) detector. we optimized the evaporation technique of tetraphenyl butadiene (TPB) on the detector surface and tested the operability of a silicon photomultiplier at LAr temperature. TPB converts LAr scintillations (vacuum ultraviolet light) to visible light, which can be detected using high-sensitivity photosensors. Because the light collection efficiency depends on the deposition mass of TPB on the inner surface of the detector, we constructed a well-controlled TPB evaporator to ensure reproducibility and measured the TPB deposition mass using a quartz crystal microbalance sensor. After optimizing the deposition mass of TPB (30 mu g/cm(2) on the photosensor window and 42 mu g/cm(2) on the detector wall), the observed light yield was 12.8 +/- 0.3 p.e./keVee using photomultiplier tubes with a quantum efficiency of approximately 30% for TPB-converted light. We also tested the low-temperature tolerance of the silicon photomultiplier, which has a high photon detection efficiency, in a LAr environment. It detected the LAr scintillations converted by TPB with a photon detection efficiency exceeding 50%.