Commissioning of the ArDM experiment at the Canfranc underground laboratory: First steps towards a tonne-scale liquid argon time projection chamber for Dark Matter searches

The Argon Dark Matter (ArDM) experiment consists of a liquid argon (LAr) time projection chamber (TPC) sensitive to nuclear recoils, resulting from scattering of hypothetical Weakly Interacting Massive Particles (WIMPs) on argon targets. With an active target mass of 850 kg ArDM represents an important milestone towards developments for large LAr Dark Matter detectors. Here we present the experimental apparatus currently installed underground at the Laboratorio Subterráneo de Canfranc (LSC), Spain. We show data on gaseous or liquid argon targets recorded in 2015 during the commissioning of ArDM in single phase at zero E-field (ArDM Run I). The data confirms the overall good and stable performance of the ArDM tonne-scale LAr detector.ISSN:1475-751

Backgrounds and pulse shape discrimination in the ArDM liquid argon TPC

The ArDM experiment completed a single-phase commissioning run (ArDM Run I) with an active liquid argon target of nearly one tonne in mass. The analysis of the data and comparison to predictions from full detector simulations allowed extraction of the detector properties and an assessment of the low background conditions. The 39Ar specific activity from the employed atmospheric argon is measured to be (0.95±0.05) Bq/kg. The cosmic muon flux at the Canfranc underground site was determined to be in the range (2–3.5)× 10−3m−2s−1. The statistical rejection power for electronic recoil events using the pulse shape discrimination method was estimated using a 252Cf neutron calibration source. Electronic and nuclear recoil band profiles were found to be well described by Gaussian distributions. Employing such a model we derive values for the electronic recoil statistical rejection power of more than 108 in the tonne-scale liquid argon target for events with more than 50 detected photons at a 50% acceptance for nuclear recoils. The 222Rn emanation rate of the ArDM cryostat at room temperature was found to be (65.6±0.4) μHz/l. These results represent an important physics milestone for the next run in the double-phase mode and in the context of foreseen developments towards the use of depleted argon targets.ISSN:1475-751