No abstract

No abstract

Abstract.A new method of searching for dark matter in the form of weakly interacting massive particles (WIMP) has been developed with the direct detection of the low energy nuclear recoils observed in a massive target (ultimately many tons) of ultra pure Liquid Argon at 87 K. A high selectivity for Argon recoils is achieved by the simultaneous observation of both the VUV scintillation luminescence and of the electron signal surviving columnar recombination, extracted through the liquid-gas boundary by an electric field.First physics results from this method are reported, based on a small 2.3 litre test chamber filled with natural Argon and an accumulated fiducial exposure of about 100 kg x day, supporting the future validity of this method with isotopically purified 40 Ar and for a much larger unit presently under construction with correspondingly increased sensitivities.We would like to dedicate this paper to the memory of our colleague and friend Nicola Ferrari.

A dedicated test of the effects of Nitrogen contamination in liquid Argon has been performed at the INFN-Gran Sasso Laboratory (LNGS, Italy) within the WArP R&D program.A detector has been designed and assembled for this specific task and connected to a system for the injection of controlled amounts of gaseous Nitrogen into the liquid Argon. Purpose of the test is to detect the reduction of the Ar scintillation light emission as a function of the amount of the Nitrogen contaminant injected in the Argon volume. A wide concentration range, spanning from ∼10 −1 ppm up to ∼10 3 ppm, has been explored.Measurements have been done with electrons in the energy range of minimum ionizing particles (γ-conversion from radioactive sources). Source spectra at different Nitrogen contaminations are analyzed, showing sensitive reduction of the scintillation yield at increasing concentrations.The rate constant of the light quenching process induced by Nitrogen in liquid Ar has been found to be k(N 2 )=0.11 µs −1 ppm −1 .Direct PMT signals acquisition at high time resolution by fast Waveform recording allowed to extract with high precision the main characteristics of the

Open questions are still present in fundamental Physics and Cosmology, like the nature of Dark Matter, the matter-antimatter asymmetry and the validity of the particle