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The ArDM experiment completed a single-phase commissioning run in 2015 with an active liquid argon target of nearly one tonne in mass. The analysis of the data and comparison to simulations allowed for a test of the crucial detector properties and confirmed the low background performance of the setup. The statistical rejection power for electron recoil events using the pulse shape discrimination method was estimated using data from a Cf-252 neutron calibration source. Electron and nuclear recoil band profiles were found to be well described by Gaussian distributions. Employing such a model we derive values for the electron recoil statistical rejection power of more than 10\\(^8\\) in the tonne-scale liquid argon target for events with more than 50 detected photons at a 50% acceptance for nuclear recoils. The Rn-222 emanation rate of the ArDM cryostat at room temperature was found to be 65.6\\(\\pm\\)0.4 \\(\\mu\\)Hz/l, and the Ar-39 specific activity from the employed atmospheric argon to be 0.95\\(\\pm\\)0.05 Bq/kg. The cosmic muon flux at the Canfranc underground site was determined to be between 2 and 3.5\\(\\times 10^{-3}m^{2}s^{-1}\\) . These results pave the way for the next physics run of ArDM in the double-phase operational mode.

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 of 850 kg, ArDM represents an important milestone in the quest for Dark Matter with LAr. We present the experimental apparatus currently installed underground at the Laboratorio Subterraneo de Canfranc (LSC), Spain. We show first data recorded during a single-phase commissioning run in 2015 (ArDM Run I), which overall confirm the good and stable performance of the ton-scale LAr detector.

WIMPs (Weakly Interacting Massive Particles) are considered the main candidates for Cold Dark Matter. The ArDM experiment aims at measuring signals directly induced by WIMPs in liquid argon. A 1-ton prototype is currently developed with the goal of demonstrating the feasibility and performance of a detector with such a large target mass. ArDM aims at acting as a liquid argon TPC and additionally measuring the scintillation light. The principle of the experiment and the conceptual design of the detector are described.

ArDM is a new-generation WIMP detector which will measure simultaneously light and charge from scintillation and ionization of liquid argon. Our goal is to construct, characterize and operate a 1 ton liquid argon underground detector. The project relies on the possibility to extract the electrons produced by ionization from the liquid into the gas phase of the detector, to amplify and read out with Large Electron Multipliers detectors. Argon VUV scintillation light has to be converted with wavelength shifters such as TetraPhenyl Butadiene in order to be detected by photomultipliers with bialkali photocathodes. We describe the status of the LEM based charge readout and light readout system R&D and the first light readout tests with warm and cold argon gas in the full size detector.

The ArDM project aims at developing and operating large noble liquid detectors to search for direct evidence of Weakly Interacting Massive Particles (WIMP) as Dark Matter in the Universe. The initial goal is to design, assemble and operate an approximately 1 ton liquid argon prototype based on the double-phase detection principle to demonstrate the feasibility of a ton-scale experiment with the required performance to efficiently detect and sufficiently discriminate backgrounds for a successful WIMP detection. The detector will independently measure the primary scintillation light and the ionization charge. This paper will mainly describe the concept, R&D results and status of the charge read out system.

The Argon Dark Matter (ArDM-1t) experiment is a ton-scale liquid argon (LAr) double-phase time projection chamber designed for direct Dark Matter searches. Such a device allows to explore the low energy frontier in LAr with a charge imaging detector. The ionization charge is extracted from the liquid into the gas phase and there amplified by the use of a Large Electron Multiplier in order to reduce the detection threshold. Direct detection of the ionization charge with fine spatial granularity, combined with a measurement of the amplitude and time evolution of the associated primary scintillation light, provide powerful tools for the identification of WIMP interactions against the background due to electrons, photons and possibly neutrons if scattering more than once. A one ton LAr detector is presently installed on surface at CERN to fully test all functionalities and it will be soon moved to an underground location. We will emphasize here the lessons learned from such a device for the design of a large LAr TPC for neutrino oscillation, proton decay and astrophysical neutrinos searches.

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.

ArDM-1t is the first operating ton-scale liquid argon detector for direct search of Dark Matter particles. Developed at CERN as Recognized Experiment RE18, the experiment has been approved in 2010 to be installed in the Spanish underground site LSC (Laboratorio Subterraneo de Canfranc). Under the label of LSC EXP-08-2010 the ArDM detector underwent an intensive period of technical completion and safety approval until the recent filling of the target vessel with almost 2 ton of liquid argon. This report describes the experimental achievements during commissioning of ArDM and the transition into a stage of first physics data taking in single phase operational mode. We present preliminary observations from this run. A first indication for the background discrimination power of LAr detectors at the ton-scale is shown. We present an outlook for completing the detector with the electric drift field and upgrade of the scintillation light readout system with novel detector modules based on SiPMs in order to improve the light yield.

ArDM-1t is the prototype for a next generation WIMP detector measuring both the scintillation light and the ionization charge from nuclear recoils in a 1-ton liquid argon target. The goal is to reach a minimum recoil energy of 30\\,keVr to detect recoiling nuclei. In this paper we describe the experimental concept and present results on the light detection system, tested for the first time in ArDM on the surface at CERN. With a preliminary and incomplete set of PMTs, the light yield at zero electric field is found to be between 0.3-0.5 phe/keVee depending on the position within the detector volume, confirming our expectations based on smaller detector setups.

The Argon Dark Matter (ArDM-1t) experiment is a ton-scale liquid argon (LAr) double-phase time projection chamber designed for direct Dark Matter searches. Such a device allows to explore the low energy frontier in LAr. After successful operation on surface at CERN, the detector has been deployed underground and is presently commissioned at the Canfranc Underground Laboratory (LSC). In this paper, we describe the status of the installation and present first results on data collected in gas phase.