C. Vignoli

Oxygen contamination in liquid Argon: combined effects on ionization electron charge and scintillation light

A dedicated test of the effects of Oxygen contamination in liquid Argon has been performed at the INFN-Gran Sasso Laboratory (LNGS, Italy) within the WArP R&D program. Two detectors have been used: the WArP2.3 lt prototype and a small (0.7 lt) dedicated detector, coupled with a system for the injection of controlled amounts of gaseous Oxygen. O2 contamination in LAr leads to depletion of both the free electron charge (via attachment process) and the scintillation light (via quenching and absorption mechanisms) available for ionization signal detection. Purpose of the test with the 0.7 lt detector was to detect the reduction of the long-lived component lifetime of the Argon scintillation light emission and of the overall light yield at increasing O2 concentration. Data from the WArP prototype were used for determining the behavior of both the ionization electron lifetime and the scintillation long-lived component lifetime at decreasing O2 concentration by the purification process activated in closed loop during the acquisition run. The electron lifetime measurements allowed to infer the O2 content of the Argon and correlate it with the long-lived scintillation lifetime data. The effects of Oxygen contamination on the scintillation light have been thus extensively measured over a wide range of O2 concentration, spanning from ~ 10−3 ppm up to ~ 10 ppm.

Scintillation efficiency of nuclear recoil in liquid xenon

Abstract We present the results of a test done with a Liquid Xenon (LXe) detector for “Dark Matter” search, exposed to a neutron beam to produce nuclear recoil events simulating those which would be generated by WIMPs elastic scattering. The aim of the experiment was to measure directly the scintillation efficiency of nuclear recoil. The nuclear recoil considered in the test was in the tens of keV range. The ratio of measured visible energy over the true recoil energy was evaluated to be about 20%, in good agreement with the theoretical predictions.

A search for the analogue to Cherenkov radiation by high energy neutrinos at superluminal speeds in ICARUS

Abstract The OPERA Collaboration (2011) [1] has reported evidence of superluminal ν μ propagation between CERN and the LNGS. Cohen and Glashow (2011) [2] argued that such neutrinos should lose energy by producing photons and e + e − pairs, through Z 0 mediated processes analogous to Cherenkov radiation. In terms of the parameter δ ≡ ( v ν 2 − v c 2 ) / v c 2 , the OPERA result corresponds to δ ≈ 5 ⋅ 10 − 5 . For this value (note that ( v ν − v c ) / v c ≈ δ 2 ≈ 2.5 ⋅ 10 − 5 ) of δ , a very significant deformation of the neutrino energy spectrum and an abundant production of photons and e + e − pairs should be observed at LNGS. We present an analysis based on the 2010 and part of the 2011 data sets from the ICARUS experiment, located at Gran Sasso National Laboratory and using the same neutrino beam from CERN. We find that the rates and deposited energy distributions of neutrino events in ICARUS agree with the expectations for an unperturbed spectrum of the CERN neutrino beam, as also reported by OPERA. Our results therefore refute a superluminal interpretation of the OPERA result according to the Cohen and Glashow (2011) prediction [2] for a weak current analog to Cherenkov radiation. In a dedicated search, no superluminal Cherenkov-like e + e − pair or γ emission event has been directly observed inside the fiducial volume of the “bubble chamber-like” ICARUS TPC-LAr detector, setting the much stricter limit of δ 2.5 ⋅ 10 − 8 at the 90% confidence level, comparable with the one due to the observations from the SN1987a (M.J. Longo, 1987 [4] ). The observations of high energy neutrino events by Super-Kamiokande and IceCube are also pointing to a much stricter limit on δ .

Performance of a liquid argon time projection chamber exposed to the CERN West Area Neutrino Facility neutrino beam

F. Arneodo, P. Benetti, M. Bonesini, A. Borio di Tigliole, B. Boschetti, A. Bueno, E. Calligarich, F. Casagrande, a D. Cavalli, F. Cavanna, P. Cennini, S. Centro, E. Cesana, D. Cline, A. Curioni, b I. De Mitri, C. De Vecchi, 2 R. Dolfini, A. Ferrari, A. Ghezzi, A . Guglielmi, J. Kisiel, G. Mannocchi, A. Mart́ınez de la Ossa, C. Matthey, F. Mauri, C. Montanari, S. Navas, P. Negri, M. Nicoletto, S. Otwinowski, M. Paganoni, O. Palamara, A. Pepato, L. Periale, G. Piano Mortari, P. Picchi, 5 F. Pietropaolo, A. Puccini, A. Pullia, S. Ragazzi, T. Rancati, A. Rappoldi, G.L. Raselli, N. Redaelli, E. Rondio, A. Rubbia, C. Rubbia, P.R. Sala, F. Sergiampietri, J. Sobczyk, S. Suzuki, 5, c T. Tabarelli de Fatis, M. Terrani, F. Terranova, A. Tonazzo, S. Ventura, C. Vignoli, H. Wang, and A. Zalewska

Detection of scintillation light in coincidence with ionizing tracks in a liquid argon time projection chamber

A system to detect light from liquid argon scintillation has been implemented in a small, ICARUS-like, liquid argon time projection chamber. The system, which uses a VUV-sensitive photomultiplier to collect the light, has recorded many ionizing tracks from cosmic-rays in coincidence with scintillation signals. Our measurements demonstrate that scintillation light detection can provide an effective method for absolute time measurement of events and eventually a useful trigger signal

Calibration of BC501A liquid scintillator cells with monochromatic neutron beams

Abstract The recoil proton energy response has been measured by exposing cylindrical cells, filled with BC501A BICRON liquid scintillator, to mono-energetic neutron reference fields. We determine the required calibration parameters and report the detailed procedures for the experimental data handling. A dedicated Monte Carlo simulation of the detector response and efficiency has been performed. It showed good agreement with the measured quantities. The results from this calibration are necessary for a detailed study of the neutron spectrum at the underground Gran Sasso Laboratory, with a neutron detector made of 32 liquid scintillator cells, like those used during the calibration.

Demonstration and comparison of photomultiplier tubes at liquid Argon temperature

Liquified noble gases are widely used as a target in direct Dark Matter searches. Signals from scintillation in the liquid, following energy deposition from the recoil nuclei scattered by Dark Matter particles (e.g. WIMPs), should be recorded down to very low energies by photosensors suitably designed to operate at cryogenic temperatures. Liquid Argon based detectors for Dark Matter searches currently implement photo multiplier tubes for signal read-out. In the last few years PMTs with photocathodes operating down to liquid Argon temperatures (87 K) have been specially developed with increasing Quantum Efficiency characteristics. The most recent of these, Hamamatsu Photonics Mod. R11065 with peak QE up to about 35%, has been extensively tested within the R&D program of the WArP Collaboration. During these testes the Hamamatsu PMTs showed superb performance and allowed obtaining a light yield around 7 phel/keVee in a Liquid Argon detector with a photocathodic coverage in the 12% range, sufficient for detection of events down to few keVee of energy deposition. This shows that this new type of PMT is suited for experimental applications, in particular for new direct Dark Matter searches with LAr-based experiments.

Precise 3D Track Reconstruction Algorithm for the ICARUS T600 Liquid Argon Time Projection Chamber Detector

Liquid Argon Time Projection Chamber (LAr TPC) detectors offer charged particle imaging capability with remarkable spatial resolution. Precise event reconstruction procedures are critical in order to fully exploit the potential of this technology. In this paper we present a new, general approach to 3D reconstruction for the LAr TPC with a practical application to the track reconstruction. The efficiency of the method is evaluated on a sample of simulated tracks. We present also the application of the method to the analysis of stopping particle tracks collected during the ICARUS T600 detector operation with the CNGS neutrino beam.

The WArP experiment

Cryogenic noble liquid detectors are presently considered one of the best options for WIMP Dark Matter searches, especially when extensions to multi ton scale sensitive masses are foreseen. The WArP experiment is the first one that exploits the unique characteristics of liquid Argon to make a highly sensitive search for WIMP Dark Matter candidates. In 2008, a double phase detector has been assembled in the Gran Sasso National Laboratory with 140 kg sensitive mass and a discovery potential in the range of 5 × 10−45 cm2 in the spin-independent WIMP-nucleon cross-section. In addition to standard neutrons and gamma-rays passive shields, WArP implements an 8 ton liquid Argon active shield with 4π coverage. The detector was commissioned and put into operation during the first half of 2009 for a first technical run. This first run lasted about three months and then it was stopped for some detector repairs and modifications in the summer of 2009. A second run was started at the beginning of 2010. Detector design, construction and assembly are described, together with the results of the technical run and the very first results of the 2010 run.

Improving the performance of the liquid argon TPC by doping with tetra-methyl-germanium

Abstract In order to recover the charge lost by electron-ion recombination, we doped pure liquid argon with a photosensitive hydrocarbon, tetra-methyl-germanium (TMG), in the 3 ton ICARUS TPC. A charge increase of 25% to 220% was observed for different electric fields and for energy densities ranging from 1.6 to 32 MeV/cm.