The HAWC TeV gamma-ray Observatory

Ground-based gamma-ray astronomy has historically implemented two dramatically different techniques. One method employs Imaging Atmospheric Cherenkov Telescope(s) (IACT) that detect the Cherenkov light generated in the atmosphere by extensive air showers. The other method employs particle detectors that directly detect the particles that reach ground level—known as Extensive Air Shower (EAS) arrays. Until recently, the IACT method had been the only technique to yield solid detections of TeV gamma-ray sources. Utilizing water Cherenkov technology, Milagro, was the first EAS array to discover new gamma-ray sources and demonstrated the power of and need for an all-sky high duty-cycle instrument in the TeV energy regime. The transient nature of many TeV sources, the enormous number of potential sources, and the existence of TeV sources that encompass large angular areas all point to the need for an all-sky, high duty-factor instrument with even greater sensitivity than Milagro. The High AltitudeWater Cherenkov (HAWC) Observatory will be over an order of magnitude more sensitive than Milagro. In this paper we will discuss the design and sensitivity of HAWC

Determination and study of the cosmic-ray composition above 100 TeV

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The goal of this project was to develop a new technique using ground-based measurements to determine the cosmic-ray composition at energies around 10{sup 15} eV (the knee in the cosmic-ray spectrum). Cosmic rays are high-energy nuclei that continuously bombard the earth. Though cosmic rays were first detected in the 1870s it wasn`t until 1915 that their cosmic origin was established. At present, the authors still do not know the source of cosmic rays. At energies above 50 TeV (1 TeV = 1 trillion electron-volts) they do not know the composition of the cosmic rays. At about 5 PeV (1PeV = 10{sup 15} eV) the cosmic ray spectrum steepens. Knowledge of the composition above and below this point can help determine the origin of cosmic rays

Evidence for an axion-like particle from PKS 1222+216?

The surprising discovery by MAGIC of an intense, rapidly varying emission in the energy range 70 - 400 GeV from the flat spectrum radio quasar PKS 1222+216 represents a challenge for all interpretative scenarios. Indeed, in order to avoid absorption of \gamma rays in the dense ultraviolet radiation field of the broad line region (BLR), one is forced to invoke some unconventional astrophysical picture, like for instance the existence of a very compact (r\sim 10^{14} cm) emitting blob at a large distance (R \sim10^{18} cm) from the jet base. We offer the investigation of a scenario based on the standard blazar model for PKS 1222+216 where \gamma rays are produced close to the central engine, but we add the new assumption that inside the source photons can oscillate into axion-like particles (ALPs), which are a generic prediction of several extensions of the Standard Model of elementary particle interactions. As a result, a considerable fraction of very-high-energy photons can escape absorption from the BLR through the mechanism of photon-ALP oscillations much in the same way as they largely avoid absorption from extragalactic background light when propagating over cosmic distances in the presence of large-scale magnetic fields in the nG range. In addition we show that the above MAGIC observations and the simultaneous Fermi/LAT observations in the energy range 0.3 - 3 GeV can both be explained by a standard spectral energy distribution for experimentally allowed values of the model parameters. In particular, we need a very light ALP just like in the case of photon-ALP oscillations in cosmic space. Moreover, we find it quite tantalizing that the most favorable value of the photon-ALP coupling happens to be the same in both situations. Although our ALPs cannot contribute to the cold dark matter, they are a viable candidate for the quintessential dark energy. [abridged]Comment: 32 pages, 10 figures, accepted for publication in Physical Review

Silicon-based resonant-cavity-enchanced photodiode with a buried SiO2 reflector

We report on a silicon-based resonant cavity photodiode with a buried silicon dioxide layer as the bottom reflector. The buried oxide is created by using a separation by implantation of oxygen technique. The device shows large Fabry-Perot oscillations. Resonant peaks and antiresonant troughs are observed as a function of the wavelength, with a peak responsivity of about 50 mA/W at 650 and 709 nm. The leakage current density is 85 pA/mm(2) at -5 V, and the average zero-bias capacitance is 12 pF/mm(2). We also demonstrate that the buried oxide prevents carriers generated deep within the substrate from reaching the top contacts, thus removing any slow carrier diffusion tail from the impulse response. (C) 1999 American Institute of Physics. (DOI: 10.1063/1.123499)

ADMX-Orpheus First Search for 70 μ\mueV Dark Photon Dark Matter: Detailed Design, Operations, and Analysis

Dark matter makes up 85% of the matter in the universe and 27% of its energy density, but we don't know what comprises dark matter. It is possible that dark matter may be composed of either axions or dark photons, both of which can be detected using an ultra-sensitive microwave cavity known as a haloscope. The haloscope employed by ADMX consists of a cylindrical cavity operating at the TM$_{010}$ mode and is sensitive to the QCD axion with masses of few $\mu$eV. However, this haloscope design becomes challenging to implement for higher masses. This is because higher masses require smaller-diameter cavities, consequently reducing the detection volume which diminishes the detected signal power. ADMX-Orpheus mitigates this issue by operating a tunable, dielectrically-loaded cavity at a higher-order mode, allowing the detection volume to remain large. This paper describes the design, operation, analysis, and results of the inaugural ADMX-Orpheus dark photon search between 65.5 $\mu$eV (15.8 GHz) and 69.3 $\mu$eV (16.8 GHz), as well as future directions for axion searches and for exploring more parameter space.Comment: 21 pages, 29 figures. To be submitted to Physical Review D. arXiv admin note: substantial text overlap with arXiv:2112.0454