Optimization of operation and test of large size GEM detectors

We describe basic development work aimed at the realization of large (~1000 cm2 active) detectors for the COMPASS experiment, based on the gas electron multiplier technology. Essentially a high-rate forward spectrometer, the experiment requires high accuracy tracking of scattered particles and light detectors, in order not to degrade mass resolution and particle identification. The choice of a double GEM structure with two-coordinate read-out fulfils the above requirements. Systematic studies confirm the required performances, with good safety margins for an operation in harsh environments. We discuss the design problems encountered in the construction of the large devices and the solutions adopted, together with preliminary results obtained with prototypes in the laboratory and in a high intensity beam

Development and test of large size GEM detectors

We discuss the main operating features of GEM detectors, optimized for use as trackers in a high radiation environment. The construction, tests and performances of large prototypes for the COMPASS experiment are also described, as well as the results of an exposure to very high intensity beams. (11 refs)

Further developments of the gas electron multiplier (GEM)

We describe the development and operation of the Gas Electron Multiplier, a thin insulating foil metal-clad on both sides and perforated by a regular pattern of small holes. The mesh can be incorporat ed in the gas volume of an active detector to provide a first amplification channel for electrons, or used as stand alone. We report on the basic properties of GEMs manufactured with different geometr ies and operated in several gas mixtures as well as on their long-term stability after accumulation of charge equivalent to several years of operation in high luminosity experiments. Optimized GEMs re ach gains close to 10000 at safe operating voltages, permitting the detection of ionizing tracks, without other amplifying elements, on a simple printed circuit board (PCB), opening new possibilities for detector design

The CAST Time Projection Chamber

One of the three X-ray detectors of the CAST experiment searching for solar axions is a Time Projection Chamber (TPC) with a multi-wire proportional counter (MWPC) as a readout structure. Its design has been optimized to provide high sensitivity to the detection of the low intensity X-ray signal expected in the CAST experiment. A low hardware threshold of 0.8 keV is safely set during normal data taking periods, and the overall efficiency for the detection of photons coming from conversion of solar axions is 62 %. Shielding has been installed around the detector, lowering the background level to 4.10 x 10^-5 counts/cm^2/s/keV between 1 and 10 keV. During phase I of the CAST experiment the TPC has provided robust and stable operation, thus contributing with a competitive result to the overall CAST limit on axion-photon coupling and mass.Comment: 19 pages, 11 figures and images, submitted to New Journal of Physic

Melatonin affects the motility and adhesiveness of in vitro capacitated boar spermatozoa via a mechanism that does not depend on intracellular ROS levels

This work sought to address the effects of melatonin during in vitro capacitation (IVC) and progesterone-induced acrosome exocytosis (IVAE) in boar spermatozoa. With this purpose, two different experiments were set. In the first one, IVC and IVAE were induced in the absence or presence of melatonin, which was added either at the start of IVC or upon triggering the IVAE with progesterone. Different parameters were evaluated, including intracellular levels of peroxides and superoxides, free cysteine radicals and distribution of specific lectins. While melatonin neither affected most capacitation-associated parameters nor IVAE, it dramatically decreased sperm motility, with a maximal effect at 5 µm. This effect was accompanied by a significant increase in the percentage of agglutinated spermatozoa, which was independent from noticeable changes in the distribution of lectins. Levels of free cysteine radicals were significantly lower in melatonin treatments than in the control after 4 h of incubation in capacitating medium. The second experiment evaluated the effects of melatonin on in vitro fertilising ability of boar spermatozoa. Spermatozoa previously subjected to IVC in the presence of 1 µm melatonin and used for in vitro fertilisation exhibited less ability to bind the zona pellucida (ZP) and higher percentages of monospermy. In conclusion, melatonin affects sperm motility and the stability of nucleoprotein structure and also modulates the ability of in vitro capacitated boar spermatozoa to bind the oocyte ZP. However, such effects do not seem to be related to either its antioxidant properties or changes in the sperm glycocalix

The Drift Chambers Of The Nomad Experiment

We present a detailed description of the drift chambers used as an active target and a tracking device in the NOMAD experiment at CERN. The main characteristics of these chambers are a large area, a self supporting structure made of light composite materials and a low cost. A spatial resolution of 150 microns has been achieved with a single hit efficiency of 97%.Comment: 42 pages, 26 figure

Construction, test and commissioning of the triple-GEM tracking detector for COMPASS

The Small Area Tracking system of the COMPASS experiment at CERN includes a set of 20 large area, fast position-sensitive Gas Electron Multiplier (GEM) detectors, designed to reliably operate in the harsh radiation environment of the experiment. We describe in detail the design, choice of materials, assembly procedures and quality controls used to manufacture the devices. The test procedure in the laboratory, the performance in test beams and in the initial commissioning phase in the experiment are presented and discussed

Prospects for the CERN Axion Solar Telescope Sensitivity to 14.4 keV Axions

The CERN Axion Solar Telescope (CAST) is searching for solar axions using the 9.0 T strong and 9.26 m long transverse magnetic field of a twin aperture LHC test magnet, where axions could be converted into X-rays via reverse Primakoff process. Here we explore the potential of CAST to search for 14.4 keV axions that could be emitted from the Sun in M1 nuclear transition between the first, thermally excited state, and the ground state of 57Fe nuclide. Calculations of the expected signals, with respect to the axion-photon coupling, axion-nucleon coupling and axion mass, are presented in comparison with the experimental sensitivity.Comment: 4 pages, 1 figure. Submitted to Nucl. Instr. and Meth.

X-ray emission during the muonic cascade in hydrogen

We report our investigations of X rays emitted during the muonic cascade in hydrogen employing charge coupled devices as X-ray detectors. The density dependence of the relative X-ray yields for the muonic hydrogen lines (K_alpha, K_beta, K_gamma) has been measured at densities between 0.00115 and 0.97 of liquid hydrogen density. In this density region collisional processes dominate the cascade down to low energy levels. A comparison with recent calculations is given in order to demonstrate the influence of Coulomb deexcitation.Comment: 5 pages, Tex, 4 figures, submitted to Physical Review Letter

First results from the CERN Axion Solar Telescope (CAST)

Hypothetical axion-like particles with a two-photon interaction would be produced in the Sun by the Primakoff process. In a laboratory magnetic field (``axion helioscope'') they would be transformed into X-rays with energies of a few keV. Using a decommissioned LHC test magnet, CAST has been running for about 6 months during 2003. The first results from the analysis of these data are presented here. No signal above background was observed, implying an upper limit to the axion-photon coupling < 1.16 10^{-10} GeV^-1 at 95% CL for m_a <~0.02 eV. This limit is comparable to the limit from stellar energy-loss arguments and considerably more restrictive than any previous experiment in this axion mass range.Comment: 4 pages, accepted by PRL. Final version after the referees comment