53630528
Simulation of VUV electroluminescence in micropattern gaseous detectors: the case of GEM and MHSP
Electroluminescence produced during avalanche development in gaseous avalanche detectors is a useful information for triggering, calorimetry and tracking in gaseous detectors. Noble gases present high electroluminescence yields, emitting mainly in the VUV region. The photons can provide signal readout if appropriate photosensors are used. Micropattern gaseous detectors are good candidates for signal amplification in high background and/or low rate experiments due to their high electroluminescence yields and radiopurity. In this work, the VUV light responses of the Gas Electron Multiplier and of the Micro-Hole & Strip Plate, working with pure xenon, are simulated and studied in detail using a new and versatile C++ toolkit. It is shown that the solid angle subtended by a photosensor placed below the microstructures depends on the operating conditions. The obtained absolute EL yields, determined for different gas pressures and as functions of the applied voltage, are compared with those determined experimentally.
122398469
Doppler-shifted nuclear gamma rays following stopped K− capture in aluminium
Abstract The Doppler broadened 26 Mg * decay gamma peak hasma peak has been observed in coincidence with stopped kaons in an Al target. The results are compared with predictions based on single-nucleon absorption of the kaon.
120683548
Large-area low-pressure microstrip gas chambers for thermal neutron imaging
Abstract Thermal neutron imaging gas detectors using counting gas mixtures with gaseous neutron convertors (e.g. 3 He) suffer from inherent limitations in position and time-of-flight resolutions resulting from the long ranges of the released secondary ions in the counting gas and from parallax errors due to the necessary depth of the detector gas volume of >1 cm. In order to overcome these limitations a novel detector generation is presently being constructed utilizing composite neutron convertor foils ( 157 Gd or 6 Li overcoated with CsI) in combination with arrays of large-area microstrip and microdot gas chambers (MSGCs and MDOTs) which are operated in low-pressure, two-stage amplification mode and delivering unsurpassed gains. In this paper the optimization of MSGCs for low-pressure operation with 157 Gd convertors is discussed. The MSGCs are of technologically advanced, robust design, using 3 mm thick synthetic quartz substrates and two closely spaced electrode planes for true two-dimensional position readout. These metal planes are separated by a ∼3 μm thick SiO 2 /DLC double-layer deposited by means of plasma-enhanced CVD. The same fabrication technology is presently prepared for production of large-area MDOTs. The work shall be conducted in collaboration with nine teams from research institutes and industry.
120592230
A multiterm Boltzmann analysis of drift velocity, diffusion, gain and magnetic-field effects in argon-methane-water-vapour mixtures
Abstract The effect of adding water vapour to argon-methane mixtures used in TPC-type detectors is investigated using the exact multiterm Boltzmann expansion. The transverse and longitudinal diffusion coefficients and the drift velocity are calculated with an accuracy of ± 3, ± 2 and ± 1% respectively. The calculations are extended into the avalanche region and compared to avalanche gain measurements. The effect of misalignment of the electric and magnetic fields on the drift direction is also investigated.
121783594
Strong interaction effects in kaonic atoms
Abstract X-rays produced by kaons stopping in targets of S, Co, Ni, Ag and Cd have been observed. The shifts and widths of the last observed mesic X-ray due to the effects of the strong interaction have been measured. In addition, the relative yield of the sulphur K − n = 4 → 3 transition has been measured.
56301921
High rate behavior and discharge limits in micro-pattern detectors
Abstract We present and discuss a set of systematic measurements, carried out with gaseous proportional micro-pattern detectors, in order to assess their maximum gain when irradiated with high-rate soft X-rays and heavily ionizing alpha particles. The inventory of detectors tested includes: micro-strips, micromegas, micro-dot, gas electron multiplier, CAT (compteur a trous), trench (or groove), micro-CAT (or WELL) detectors, as well as systems with two elements of gaseous amplification in cascade. We confirm the general trend of all single-stage detectors to follow Raether's criterion, i.e. a spontaneous transition from avalanche to streamer, followed by a discharge, when the avalanche size reaches a value of a few 10 7 ; a noticeable exception is the micro-dot counter holding more than 10 8 . In multiple structures, where the gain is shared between two devices in cascade, the maximum overall gain under irradiation is increased by at least one order of magnitude; we speculate this to be a consequence of a voltage dependence of Raether's limit, larger for low operating potentials. Our conclusion is that only multiple devices can guarantee a sufficient margin of reliability for operation in harsh LHC running conditions.
19567091
A search for neutrino emission from the Fermi bubbles with the ANTARES telescope
Analysis of the Fermi-LAT data has revealed two extended structures above and below the Galactic Centre emitting gamma rays with a hard spectrum, the so-called Fermi bubbles. Hadronic models attempting to explain the origin of the Fermi bubbles predict the emission of high-energy neutrinos and gamma rays with similar fluxes. The ANTARES detector, a neutrino telescope located in the Mediterranean Sea, has a good visibility to the Fermi bubble regions. Using data collected from 2008 to 2011 no statistically significant excess of events is observed and therefore upper limits on the neutrino flux in TeV range from the Fermi bubbles are derived for various assumed energy cutoffs of the source.
110859812
The Central Logic Board and its auxiliary boards for the optical module of the KM3Net detector
The KM3Net neutrino telescope will be composed of many optical modules, each of them containing 31 (3") photomultipliers, connected to a Central Logic Board. The Central Logic Board integrates Time to Digital Converters that measure Time over Threshold of the photomultipliers signals while White Rabbit is used for the optical modules time synchronization. Auxiliary boards have also been designed and built in order to test and extend the performance of the Central Logic Board. The Central Logic Board, as well as the auxiliary boards, will be presented by focusing on the design consideration, prototyping issues and tests.
123084986
Long-term optical background measurements in the Capo Passero deep-sea site
In March 2013, the Nemo Phase-2 tower has been successfully installed at 100 km off-shore Capo Passero (Italy) and 3500 m depth. This 8-floor tower hosts 32 10-inch PMT's. Results from optical background measurements are presented. In particular, the analyzed rates show stable and low baseline values, compatible with the contribution of 40K light emission, with a small percentage of light bursts due to bioluminescence. All these features are a confirmation of the stability and good optical nature of the site.
118018120
First results on dark matter annihilation in the Sun using the ANTARES neutrino telescope
A search for high-energy neutrinos coming from the direction of the Sun has been performed using the data recorded by the ANTARES neutrino telescope during 2007 and 2008. The neutrino selection criteria have been chosen to maximize the selection of possible signals produced by the self-annihilation of weakly interacting massive particles accumulated in the centre of the Sun with respect to the atmospheric background. After data unblinding, the number of neutrinos observed towards the Sun was found to be compatible with background expectations. The 90% CL upper limits in terms of spin-dependent and spin-independent WIMP-proton cross-sections are derived and compared to predictions of two supersymmetric models, CMSSM and MSSM-7. The ANTARES limits are comparable with those obtained by other neutrino observatories and are more stringent than those obtained by direct search experiments for the spin-dependent WIMP-proton cross-section in the case of hard self-annihilation channels (W+W-, tau(+)tau(-)).
120208422
The KM3NeT Project
The KM3NeT consortium has been carrying on R&D activities towards the construction of a km3 scale deep sea neutrino telescope to detect high-energy astrophysical neutrinos. It will complement the IceCube detector, already in operation at the South Pole, and will have the Galactic centre and most of the Galactic plane in its field of view. Recently a technical design report has been released which contains the general description of the KM3NeT deep sea research infrastructure. This research facility will represent also a multidisciplinary marine and Earth science observatory, hosting a network of nodes for long term continuous monitoring of the deep sea environment. The objectives, status and plans of the KM3NeT project are presented.