54083034
Overcoming real-world obstacles in 21 cm power spectrum estimation: A method demonstration and results from early Murchison Widefield Array data
We present techniques for bridging the gap between idealized inverse covariance weighted quadratic estimation of 21 cm power spectra and the real-world challenges presented universally by interferometric observation. By carefully evaluating various estimators and adapting our techniques for large but incomplete data sets, we develop a robust power spectrum estimation framework that preserves the so-called \EoR window" and keeps track of estimator errors and covariances. We apply our method to observations from the 32-tile prototype of the Murchinson Wideeld Array to demonstrate the importance of a judicious analysis technique. Lastly, we apply our method to investigate the dependence of the clean EoR window on frequency|especially the frequency dependence of the so-called \wedge" feature|and establish upper limits on the power spectrum from z = 6:2 to z = 11:7. Our lowest limit is
125296828
Constraints on Fundamental Cosmological Parameters with Upcoming Epoch of Reionization Observations
122792689
Computer animation of extensive air showers interacting with the MILAGRO water Cherenkov detector
I employ advanced computer animation to visualize the interaction of Extensive Air Showers (EAS) with the Milagro water reservoir. The animations help conceptualize the evolution of the EAS particle front as it hits a large volume of water and converts to a front of Cherenkov photons. Expected effects such as refraction and curvature are easily seen, as well as a number of novel behaviors. A simple model that explains the observed dynamics of the shower front is presented.
119849397
TRASGO: A proposal for a timing RPCs based detector for analyzing cosmic ray air showers
Abstract The study of the properties of primary cosmic rays with energies above 100 TeV is only accessible indirectly through the use of detector arrays at the Earth surface. Despite the extremely high multiplicity of the air showers produced in their interactions at the highest layers of the atmosphere, only a fraction of those particles arrive to the ground over surfaces from ∼ 0.1 to ∼ 100 km 2 . The lack of information on the primary interaction and the low density of particles at the detection plane make the event by event analysis very complicated and usually only mean analysis are possible, sometimes with the help of simulation programs. The necessity of covering big surfaces to gather a significant sample of information usually leads to the use of big volume detectors with limited performances, giving only access to a small part of the information carried out by the swarm of secondary particles of the shower. In this article, we propose the development of an affordable detector, the TRASGO, based on timing RPCs (Resistive Plate Chambers) offering at the same time very good timing and tracking performances. TRASGO would allow a better and more accurate reconstruction of the air shower properties either working stand-alone or in big surface arrays.
2271229
THE SENSITIVITY OF FIRST-GENERATION EPOCH OF REIONIZATION OBSERVATORIES AND THEIR POTENTIAL FOR DIFFERENTIATING THEORETICAL POWER SPECTRA
Statistical observations of the epoch of reionization (EOR) power spectrum provide a rich data set for understanding the transition from the cosmic ‘‘dark ages’’ to the ionized universe we see today. EOR observations have become an active area of experimental cosmology, and three first-generation observatories—MWA, PAST, and LOFAR—are currently under development. In this paper we provide the first quantitative calculation of the threedimensional power spectrum sensitivity, incorporating thedesign parameters of a planned array. This calculation is then used to explore the constraints these first-generation observations can place on the EOR power spectrum. The results demonstrate the potential for upcoming power spectrum observations to constrain theories of structure formation and reionization. Subject headings: early universe — intergalactic medium — radio lines: general — techniques: interferometric Online material: color figure
119242483
The Baryon Acoustic Oscillation Broadband and Broad-beam Array: Design Overview and Sensitivity Forecasts
This work describes a new instrument optimized for a detection of the neutral hydrogen 21 cm power spectrum between redshifts of 0.5 and 1.5: the Baryon Acoustic Oscillation Broadband and Broad-beam (BAOBAB) array. BAOBAB will build on the efforts of a first generation of 21 cm experiments that are targeting a detection of the signal from the Epoch of Reionization at z ~ 10. At z ~ 1, the emission from neutral hydrogen in self-shielded overdense halos also presents an accessible signal, since the dominant, synchrotron foreground emission is considerably fainter than at redshift 10. The principle science driver for these observations are baryon acoustic oscillations in the matter power spectrum which have the potential to act as a standard ruler and constrain the nature of dark energy. BAOBAB will fully correlate dual-polarization antenna tiles over the 600-900 MHz band with a frequency resolution of 300 kHz and a system temperature of 50 K. The number of antennas will grow in staged deployments, and reconfigurations of the array will allow for both traditional imaging and high power spectrum sensitivity operations. We present calculations of the power spectrum sensitivity for various array sizes, with a 35 element array measuring the cosmic neutral hydrogen fraction as a function of redshift, and a 132 element system detecting the BAO features in the power spectrum, yielding a 1.8% error on the z ~ 1 distance scale, and, in turn, significant improvements to constraints on the dark energy equation of state over an unprecedented range of redshifts from ~0.5 to 1.5.
113451453
Aging and conductivity of electrodes for high rate tRPCs from an ion conductivity approach
Resistive Plate Chambers (RPCs) are multipurpose ionizing gas detectors broadly used in Particle Physics research because of the outstanding time resolution they offer at a very affordable price, their robustness and their easy manufacture. However, to extend their use to a broader range of applications, some properties, specially the counting rate capability, need to be improved. The straightforward way to increase the rate capability is to develop new electrodes with resistivities in the range of 10 7 �10 8 .m offering, besides a “resistive” character, conductivity high enough for allowing faster charge depletion in the chamber. In this work, we have carried out electrical measurements on several materials that are currently used or, according to their conductivity values, are good candidates to be used as resistive plates in high rate RPCs. We have analysed their behaviour in order to identify and to better understand their conduction mechanisms and to determine the nature of the degradation 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.
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.
117096035
Quasinormal acoustic oscillations in the Michel flow
We study spherical and nonspherical linear acoustic perturbations of the Michel flow, which describes the steady radial accretion of a perfect fluid into a nonrotating black hole. The dynamics of such perturbations are governed by a scalar wave equation on an effective curved background geometry determined by the acoustic metric, which is constructed from the spacetime metric and the particle density and four-velocity of the fluid. For the problem under consideration in this paper the acoustic metric has the same qualitative features as an asymptotically flat, static and spherically symmetric black hole, and thus it represents a natural astrophysical analogue black hole. As for the case of a scalar field propagating on a Schwarzschild background, we show that acoustic perturbations of the Michel flow exhibit quasinormal oscillations. Based on a new numerical method for determining the solutions of the radial mode equation, we compute the associated frequencies and analyze their dependency on the mass of the black hole, the radius of the sonic horizon and the angular momentum number. Our results for the fundamental frequencies are compared to those obtained from an independent numerical Cauchy evolution, finding good agreement between the two approaches. When the radius of the sonic horizon is large compared to the event horizon radius, we find that the quasinormal frequencies scale approximately like the surface gravity associated with the sonic horizon.
120073980
Analysis of compact and sealed RPCs feasibility
In this article, the feasibility of developing compact and portable float glass sealed Resistive Plate Chambers, sRPCs, is analyzed. For this purpose, several small (80 cm 2 ) sealed chambers have been constructed using inexpensive materials like windows float glass, copper tape and nylon fishing line. For the sake of simplicity, during this first development stage, only R134a has been used as ionizing gas. In order to distinguish gas leakage from internal gas degradation, a couple of sRPCs were tested inside a box with flowing gas: one with R134a and another with N2. Prompt charge, signal rising slope and operational current were used to assess chambers performance degradation during a two-week period. Regarding these variables, small leakages were spotted as the main reason for the performance degradation observed after about one week of steady operation at the sRPC working in N2 environment. The sRPC working in an R134a environment did not show any significative degradation during the whole test. A discussion on merits and limitations of the proposed design is provided.