Secondary scintillation yield in pure argon

The secondary scintillation yield is of great importance for simulating double phase detectors, which are used in several of the ongoing Dark Matter search experiments, as well as in the future large-scale particle detectors proposed in Europe as the next generation underground observatories. The argon secondary scintillation yield is studied, at room temperature, as a function of electric field in the gas scintillation gap. A Large Area Avalanche Photodiode (LAAPD) collects the VUV secondary scintillation produced in the gas, as well as the 5.9 keV x-rays directly absorbed in the photodiode. The direct x-rays were used as a reference for the determination of the number of charge carriers produced by the scintillation pulse and, so, the number of photons impinging the LAAPD. A value of 81 photons/kV was obtained for the scintillation amplification parameter, defined as the number of photons produced per drifting electron and per kilovolt. The scintillation yields obtained in this work are in agreement with those obtained by Monte Carlo calculations and a factor of ∼10 higher than those determined by the WARP experiment.