A low background Micromegas detector for the CAST experiment

A low background Micromegas detector has been operating on the CAST experiment at CERN for the search of solar axions during the first phase of the experiment (2002-2004). The detector operated efficiently and achieved a very low level of background rejection ($5\times 10^{-5}$ counts keV$^{-1}$cm$^{-2}$s$^{-1}$) thanks to its good spatial and energy resolution as well as the low radioactivity materials used in the construction of the detector. For the second phase of the experiment (2005-2007), the detector will be upgraded by adding a shielding and including focusing optics. These improvements should allow for a background rejection better than two orders of magnitude.Comment: 6 pages, 3 figures To appear on the proceedings of the 9th ICATPP Conference on AStroparticle, Particle, Space Physics, Detectors and Medical Physics Application

The camera of the fifth H.E.S.S. telescope. Part I: System description

In July 2012, as the four ground-based gamma-ray telescopes of the H.E.S.S. (High Energy Stereoscopic System) array reached their tenth year of operation in Khomas Highlands, Namibia, a fifth telescope took its first data as part of the system. This new Cherenkov detector, comprising a 614.5 m^2 reflector with a highly pixelized camera in its focal plane, improves the sensitivity of the current array by a factor two and extends its energy domain down to a few tens of GeV. The present part I of the paper gives a detailed description of the fifth H.E.S.S. telescope's camera, presenting the details of both the hardware and the software, emphasizing the main improvements as compared to previous H.E.S.S. camera technology.Comment: 16 pages, 13 figures, accepted for publication in NIM

The CLAS12 Forward Tagger

This document presents the technical layout and the performance of the CLAS12 Forward Tagger (FT). The FT, composed of an electromagnetic calorimeter based on PbWO4 crystals (FT-Cal), a scintillation hodoscope (FT-Hodo), and several layers of Micromegas trackers (FT-Trk), has been designed to detect electrons and photons scattered at polar angles from 2∘ to 5∘ and to meet the physics goals of the hadron spectroscopy program and other experiments running with the CLAS12 spectrometer in Hall B

Constitution d'une génothèque destinée à l'identification des génomes mitochondriaux et recherche de nouvelles séquences mitochondriales chez les végétaux supérieurs

Le génome mitochondrial (mt) des plantes supérieures, dont la taille peut varier entre 200 et 560 kb, est composé d’une population hétérogène de molécules de tailles variables pouvant se recombiner grâce à la présence de séquences répétées. Les gènes présents sont constitués de séquences codantes très conservées et peuvent présenter des caractéristiques structurales comme la présence d’introns interrompus conduisant à un épissage en trans. Ces séquence codantes peuvent être utilisées comme sondes pour caractériser le polymorphisme entre variétés ou espèces. La recherche de nouvelles séquences codantes utilisables nous a amenés à identifier et caractériser 2 gènes mt nouveaux, nad5 et nad6.The mt genome of higher plants (size varying from 200 to 560 kb according to the species) consists of a heterogeneous population of molecules resulting from intra- or inter-molecular recombination. Besides the highly conserved coding sequences of mt genes, other sequences, for example, promiscuous chloroplast sequences, may be found. The genes may be interrupted by introns; in some cases, one or more introns have been split, leading to the scattering of the gene segments to remote parts of the genome ; this structure requires trans-splicing steps for the mature messenger RNA to be obtained. Over l5 genes have been identified so far that are usable, as universal polymorphism markers in RFLP (restriction fragment length polymorphism) characterization of mt genomes due to sequence conservation. During the search for new genes we identified 2 new coding sequences, nad5 and nad6; nad6 consists of a single reading frame whereas nad5 is a split gene whose 3 independent segments are independently transcribed

The CLAS12 Forward Tagger

This document presents the technical layout and the performance of the CLAS12 Forward Tagger (FT). The FT, composed of an electromagnetic calorimeter based on PbWO4 crystals (FT-Cal), a scintillation hodoscope (FT-Hodo), and several layers of Micromegas trackers (FT-Trk), has been designed to detect electrons and photons scattered at polar angles from 2? to 5? and to meet the physics goals of the hadron spectroscopy program and other experiments running with the CLAS12 spectrometer in Hall B

The CLAS12 Micromegas Vertex Tracker

The Micromegas Vertex Tracker was designed to improve upon the tracking capabilities of the baseline design of the CLAS12 spectrometer in Hall B at Jefferson Laboratory. A Barrel Micromegas Tracker made with six concentric cylinders, each made of three 120-sector tiles, surrounds the Silicon Vertex Tracker, and a Forward Micromegas Tracker composed of 6 disks is placed 30 cm downstream of the liquid-hydrogen target. Both trackers sit in a 5 T solenoid magnetic field. All Micromegas elements are based on resistive technology to withstand luminosities up to 10^35 cm−2 s−1, as well as on bulk technology to enforce gain uniformity and mechanical robustness. Due to the high magnetic field, dedicated electronics have been designed and displaced 2 m away from the detectors. The electronics readout is based on the DREAM ASICs that allow sustained operation up to 20 kHz trigger rate at the maximum luminosity

Micromegas in CAST and prospects

A low background Micromegas X-ray detector has been used to search for solar axions in the CAST experiment at CERN. The detector has an active area of 7cm times 7cm, excellent spatial resolution (~70nm), and good energy resolution. It is built using low radioactivity materials and the obtained background level is below 5times10-5 counts/keV/cm2/s. The detector is being upgraded for the second phase of the experiment (2006-2007) with a reduced active area. A focusing X-Ray optic and improved shielding will be used to further reduce the background by approximately two orders of magnitude