28772765
Conductivity and charge depletion aging of resistive electrodes for high rate RPCs
Development of new electrodes is a key element for the improvement of high rate Resistive Plate Chambers (RPC). In the particular case of resistive electrodes, the fabrication of these elements is a challenging problem from a material science point of view. The combination of resistivity, permittivity and stability requirements is really hard to satisfy for any known material. Only a few materials have been found to be suitable for fabrication of resistive plates. In this work, we have carried out electrical characterizations of some of the materials that are currently used in RPCs or are solid candidates to be used as resistive plates in high rate RPCs. As a result, we have found strong evidences that ion conduction processes under moderate to high electric fields are able to drift high amounts of charge which allow to understand the degradation nature of the involved processes.
16249880
Performances of 4-gap timing RPCs for relativistic ions in the range Z=1-6
Results from 4-gap Resistive Plate Chambers (RPCs) under irradiation by fully stripped relativistic ions (normalized momentum p/M = γβ = 2.7, atomic charge Z = 1−6) are presented. A time resolution of 80 ps at high efficiency has been obtained by using standard `off the shelf' 4-gap timing RPCs from the new HADES time-of-flight wall. The resolution worsened to 100 ps for ~ 1 kHz/cm2 proton flux and for ~ 100 Hz/cm2 carbon flux. The chambers were operated at a field E = 100 kV/cm, showing a high stability during the measurements. It seems to exist ample room for improvement, in particular regarding the time resolution.
15868099
A Search for TeV Gamma-Ray Burst Emission with the Milagro Observatory
The Milagro telescope monitors the northern sky for 100 GeV - 100 TeV transient emission through continuous very high energy wide-field observations. The large effective area and low energy threshold of Milagro allow it to detect very high energy gamma-ray burst emission with much higher sensitivity than previous instruments, and a fluence sensitivity at TeV energies comparable to dedicated gamma-ray burst satellites at keV-MeV energies. Observation of gamma-ray burst emission at TeV energies could place important constraints on gamma-ray burst progenitor and emission models. This study details the development of a weighted analysis technique; the implementation of this technique to perform a real time search for TeV transients of 40 seconds to 3 hours duration in the Milagro data; and the results from more than one year of observation. Between May 2nd, 2001, and May 22nd, 2002, no TeV transients of 40 seconds to 3 hours duration were observed. Upper limits on both observed and emitted high energy gamma-ray burst emission are presented.
160008925
Development of small easy to build and low gas consumming timing RPCs
Timing Resistive Plate Chambers (tRPCs) have become a very popular detectors due to the very good timing capability they offer for covering big surfaces at a very good performance/price ratio. However, such kind of detectors could also be very useful for small experimental setups as an alternative to other methods if their very bulky and uncomfortable gas system could be removed. They are not only very cheap, but they can be built very easily with very simple materials and a few fast electronic components. Recently, we have opened a research line aiming to develop small and portable sealed tRPCs (sRPCs) and to analyze the evolution of their performances along the time. As a first step, we built a few small one-gap and two-gap detectors and we installed in our laboratory a fast and reliable acquisition setup able to monitorize the main features of the detectors on real time. We tested some of the developed detectors under different environments and a comparison was made.
118278878
HI Structure Observations of Reionization and Dark Energy
The purpose of the talk was to review the current status of the Murchison Widefield Array (MWA), and show the applications of HI structure observations for both reionization and dark energy measurements. Since the status of the MWA is changing weekly, please see the website1 for the current status. This proceedings will instead concentrate on HI structure observations, their applicability to reionization and cosmography, and the implications for the SKA and future HI structure observations of dark energy.
13859904
FOREGROUND CONTAMINATION IN INTERFEROMETRIC MEASUREMENTS OF THE REDSHIFTED 21 cm POWER SPECTRUM
Subtraction of astrophysical foreground contamination from “dirty” sky maps produced by simulated measurements of the Murchison Widefield Array (MWA) has been performed by fitting a third-order polynomial along the spectral dimension of each pixel in the data cubes. The simulations are the first to include the unavoidable instrumental effects of the frequency-dependent primary antenna beams and synthesized array beams. They recover the onedimensional spherically binned input redshifted 21 cm power spectrum within ∼ 1% over the scales probed most sensitively by the MWA (0.01 k 1M pc −1 ) and demonstrate that realistic instrumental effects will not mask the epoch of reionization signal. We find that the weighting function used to produce the dirty sky maps from the gridded visibility measurements is important to the success of the technique. Uniform weighting of the visibility measurements produces the best results, whereas natural weighting significantly worsens the foreground subtraction by coupling structure in the density of the visibility measurements to spectral structure in the dirty sky map data cube. The extremely dense uv-coverage of the MWA was found to be advantageous for this technique and produced very good results on scales corresponding to |u| 500λ in the uv-plane without any selective editing of the uv-coverage.
51813275
WHAT NEXT-GENERATION 21 cm POWER SPECTRUM MEASUREMENTS CAN TEACH US ABOUT THE EPOCH OF REIONIZATION
A number of experiments are currently working toward a measurement of the 21 cm signal from the epoch of reionization (EoR). Whether or not these experiments deliver a detection of cosmological emission, their limited sensitivity will prevent them from providing detailed information about the astrophysics of reionization. In this work, we consider what types of measurements will be enabled by the next generation of larger 21 cm EoR telescopes. To calculate the type of constraints that will be possible with such arrays, we use simple models for the instrument, foreground emission, and the reionization history. We focus primarily on an instrument modeled after the ~0.1 km2 collecting area Hydrogen Epoch of Reionization Array concept design and parameterize the uncertainties with regard to foreground emission by considering different limits to the recently described "wedge" footprint in k space. Uncertainties in the reionization history are accounted for using a series of simulations that vary the ionizing efficiency and minimum virial temperature of the galaxies responsible for reionization, as well as the mean free path of ionizing photons through the intergalactic medium. Given various combinations of models, we consider the significance of the possible power spectrum detections, the ability to trace the power spectrum evolution versus redshift, the detectability of salient power spectrum features, and the achievable level of quantitative constraints on astrophysical parameters. Ultimately, we find that 0.1 km2 of collecting area is enough to ensure a very high significance ( 30σ) detection of the reionization power spectrum in even the most pessimistic scenarios. This sensitivity should allow for meaningful constraints on the reionization history and astrophysical parameters, especially if foreground subtraction techniques can be improved and successfully implemented.