Design of the Chicago Air Shower Array

title: Searching for the Axion
abstract: This talk focuses on the search for the axion, a hypothetical elementary particle which historically appreared in a compelling solution to the Strong-CP problem in QCD. Subsequently, the axion was recognized to be a good Cold Dark Matter candidate. Although dark matter axions have only feeble couplings to matter and radiation, extremely sensitive searches are underway around the world. In this talk we review the state of experiments searching for the axion through its coupling to photons, with emphasis on experiments that look for axions that could make up dark matter.

title: Project 8: Determining neutrino mass from tritium beta decay using a frequency-based method
abstract: A general description is given of Project 8, a new approach to measuring the neutrino mass scale via the beta decay of tritium. In Project 8, the energy of electrons emitted in beta decay is determined from the frequency of cyclotron radiation emitted as the electrons spiral in a uniform magnetic eld.

title: Design and operation of the Chicago air shower array
abstract: The Chicago Air Shower Array (CASA) is a large‐area surface scintillator array designed to study PeV sources of cosmic rays. The complete detector will consist of 1089 detector stations, distributed on a square 15 m grid. We have operated an array of 49 stations for much of the 1989 calendar year, an array of 529 stations for much of 1990, and the balance of the 1089 stations will be operating in early 1991. This surface array, together with the University of Michigan underground muon detectors (MIA), and the University of Utah atmospheric Cerenkov telescopes and Fly’s Eye air fluorescence detector, constitute a uniquely powerful instrument, dubbed the Utah Michigan Chicago (UMC) experiment, for the study of PeV sources. We report here the performance and current status of these detectors.

title: Design, construction, prototype tests and performance of a vertex chamber for the MAC detector☆
abstract: The design considerations, construction techniques, prototype tests and performance characteristics of a pressurized drift chamber used in the MAC detector at PEP are described. The chamber consists of 324 aluminized mylar tubes of 6.9 mm diameter with wall thickness of 100 μm. With appropriate shielding it operates successfully at 4.6 cm from the beam line. It was simple to construct and was configured to permit any malfunctioning tubes to be remotely disconnected without affecting operation. The chamber operated without problems for two years in the PEP environment with a gas mixture of 49.5% argon, 49.5% CO 2 , 1% CH 4 , at 4 atm absolute pressure. The mean spatial resolution averaged over all tubes was 45 μm. The time to distance relation for this gas mixture, along with the geometric positioning of individual wires relative to the central tracking chamber, was obtained with data from Bhabha scattering events. We also describe resolution studies performed with a prototype chamber in a SLAC test beam. A wide range of gases, gas pressures, and electronic parameters were explored. These studies proved that resolutions in the 10–50 μm range were possible. Our experience demonstrates that chambers of this type provide high precision tracking and are particularly suited for operation in regions with difficult physical access and/or high ambient radiation levels.

title: Properties of Ellipticity Correlation with Atmospheric Structure from Gemini South
abstract: Cosmic shear holds great promise for a precision independent measurement of Ωm, the mass density of the universe relative to the critical density. The signal is expected to be weak, so a thorough understanding of systematic effects is crucial. An important systematic effect is the atmosphere: shear power introduced by the atmosphere is larger than the expected signal. Algorithms exist to extract the cosmic shear from the atmospheric component, although a measure of their success applied to a range of seeing conditions is lacking. To gain insight into atmospheric shear, Gemini South imaging, in conjunction with ground condition and satellite wind data, was obtained. We find that under good seeing conditions point-spread function (PSF) correlations persist well beyond the separation typical of high-latitude stars. Under these conditions, ellipticity residuals based on a simple PSF interpolation can be reduced to within a factor of a few of the shot noise induced ellipticity floor. We also find that the ellipticity residuals are highly correlated with wind direction. Finally, we correct stellar shapes using a more sophisticated procedure and generate shear statistics from stars. Under all seeing conditions in our data set the residual correlations lie everywhere below the target signal level. For good seeing we find that the systematic error attributable to atmospheric turbulence is comparable in magnitude to the statistical error (shape noise) over angular scales relevant to present lensing surveys.

title: Amenability of crossed products ofC*-algebras
abstract: AbstractIt is shown that the class of amenable (resp. strongly amenable)C*-algebras is closed under the process of taking crossed products with discrete amenable groups. Under certain circumstances, amenability is also preserved under taking a “crossed product” with an amenable semigroup of linear endomorphisms. These facts are used to show that certain simpleC*-algebras
$$\mathcal{O}_n $$
 studied by J. Cuntz are amenable but not strongly amenable (thus answering a question of B. E. Johnson), yet are stably isomorphic to strongly amenable algebras.