Measurement of the attenuation length of argon scintillation light in the ArDM LAr TPC

Abstract

Abstract. We report on a measurement of the attenuation length for the scintillation light in the tonne size liquid argon target of the ArDM dark matter experiment. The data was recorded in the first underground operation of the experiment in single-phase operational mode. The results were achieved by comparing the light yield spectra from 39 Ar and 83m Kr to a description of the ArDM setup with a model of full light ray tracing. A relatively low value close to 0.5 m was found for the attenuation length of the liquid argon bulk to its own scintillation light. We interpret this result as a presence of optically active impurities in the liquid argon which are not filtered by the installed purification systems. We also present analyses of the argon gas employed for the filling and discuss cross sections in the vacuum ultraviolet of various molecules in respect to purity requirements in the context of large liquid argon installations.

Index of refraction, Rayleigh scattering length, and Sellmeier coefficients in solid and liquid argon and xenon

“…ArDM used the results of this calculation to update the optical simulation. Using this, an in situ measurement of the attenuation length was made with result of 52±7cm [15]. This is within error the predicted value.…”

“…• The ArDM collaboration published an in situ measurement of the attenuation length of liquid argon in the detector. This yield a measurement of 52±7cm [15].…”

Search for dark matter with a 231-day exposure of liquid argon using DEAP-3600 at SNOLAB

“…Figure 12 shows the difference between the z-coordinates reconstructed by both algorithms, where the z-axis runs parallel to the AV neck. Both algorithms typically agree for 39 Ar events in data and for simulations of 40 Ar recoils, returning z-coordinates that agree to within 35 mm for 50% of such events. For simulated events generated by α-decays through a LAr film on the surface of the AV neck (to be discussed in Sec.…”

“…Impurities (e.g., O 2 , N 2 ) can decrease the scintillation yield [36][37][38] of LAr by absorbing the scintillation light and, for electronegative impurities, by capturing the excitation energy from the Ar excimers. Electronegative impurities thus preferentially suppress the triplet scintillation component and affect the PSD distributions [39,40].…”

Near-infrared scintillation of liquid argon: recent results obtained with the NIR facility at Fermilab

“…This is not a concern for small volumes of LNG but indeed becomes a source of performance degradation as the volume increases and light coming from as far as 2.5 m away from the photon collection system needs to be efficiently detected [9]. A recent theoretical estimate of the Rayleigh scattering length [10] places it at 55 cm a value that seems to be supported by indirect measurements by two different DM experiments, ArDM and DarkSide-50 [11].…”