Effects of Nitrogen and Oxygen contaminations in liquid Argon

Two dedicated and distinct tests of the effects of Nitrogen and Oxygen contaminations in liquid Argon (LAr) have been performed within the WArP R&D program. Purpose of the tests is to detect the reduction of the LAr scintillation light emission as a function of the amount of the contaminant injected in the Argon volume. The rate constant of the light quenching process induced by Nitrogen in LAr has been found to be k ( N 2 ) = 0.11 μ s - 1 ppm - 1 (part per million), while the rate constant for Oxygen has been found to be k ′ ( O 2 ) = 0.54 ± 0.03 μ s - 1 ppm - 1 . Direct PMT signals acquisition allowed to extract with high precision the main characteristics of the scintillation light emission in pure and contaminated LAr. In particular, the decreasing behavior in lifetime and relative amplitude of the slow component is found to be appreciable from O (1 ppm) of Nitrogen concentrations and from O (0.1 ppm) of Oxygen concentrations.