High Energy Astrophysics Experiments Research Articles

Developing the future of gamma-ray astrophysics with monolithic silicon pixels

This paper explores the potential of AstroPix, a project to develop Complementary Metal Oxide Semiconductor (CMOS) pixels for the next generation of space-based high-energy astrophysics experiments. Multimessenger astrophysics is a rapidly developing field whose upcoming missions need support from new detector technology such as AstroPix. ATLASPix, a monolithic silicon detector optimized for the ATLAS particle detector at CERN, is the beginning of the larger AstroPix project. Energy resolution is a driving parameter in the reconstruction of gamma-ray events, and therefore the characterization of ATLASPix energy resolution is the focus of this paper. The intrinsic energy resolution of the detector exceeded our baseline requirements of <10% at 60 keV. The digital output of ATLASPix results in energy resolutions insufficient to advance gamma-ray astronomy. However, the results from the intrinsic energy resolution indicate the digital capability of the detector can be redesigned, and the next generation of pixels for the larger AstroPix project have already been constructed. Iterations of AstroPix-type pixels are an exciting new technology candidate to support new space-based missions.

B. V. Sreekantan (1925–2019)

The new face of India after independence could be seen not only in dams and industries, but it was also apparent in the experiments in fundamental research undertaken with zeal by its youngsters. One of those youngsters was B. V. Sreekantan who passed away on 27 October 2019 at the ripe age of 95 years. He pioneered experiments in three fields: (1) Cosmic ray interactions and extensive air showers; (2) Underground muon and neutrino experiments; and (3) High energy astrophysics experiments. His experiments of those times are interesting for several reasons: (a) These are pioneering efforts of an individual as also of a new institution looking for new ways and means in research. (b) These would set up the roads to be travelled by the next generation of researchers. (c) The ingenuity in the face of scarcity of science instruments was very important in a newly independent and not an affluent country.

An analog-to-digital converter and intelligent controller for use in a DAQ system processing PMT signals from very high energy astrophysics experiments

Abstract Modern instrumentation for very high energy gamma-ray astronomy and astrophysics requires efficient and precise digitization of PMT signals from Cherenkov light generated by incoming cosmic ray particles over the energy range from hundreds of GeV up to several hundred TeV. This dynamic range of more than 1000 is coupled with a requirement for very low noise operation. We have developed modern multi-channel analog-to-digital converters (model BPA-8) together with a data acquisition system, managed with an intelligent crate-controller (model K-167) which controls the measurement modules. The electronics described in this paper is accepted to be used to record PMT signals with high precision and efficiency, allowing reliable extraction and precise analysis of Cherenkov signals from high energy gamma-rays emitted by astrophysical objects.

TESTING THE ORIGIN OF HIGH-ENERGY COSMIC RAYS

Recent accurate measurements of cosmic-ray (CR) protons and nuclei by ATIC-2, CREAM, and PAMELA reveal: a) unexpected spectral hardening in the spectra of CR species above a few hundred GeV per nucleon, b) a harder spectrum of He compared to protons, and c) softening of the CR spectra just below the break energy. These newly-discovered features may offer a clue to the origin of the observed high-energy Galactic CRs. We discuss possible interpretations of these spectral features and make predictions for the secondary CR fluxes and secondary to primary ratios, anisotropy of CRs, and diffuse Galactic {\gamma}-ray emission in different phenomenological scenarios. Our predictions can be tested by currently running or near-future high-energy astrophysics experiments.

On the characteristics of neutrino events in (ultra-)high energy astrophysics experiments from the view point of energy estimation

The energies of muon neutrino events with energies above 10 TeV could not be estimated in principle even in 1 cubic kilometer detectors, whilst those of electron neutrino events could be estimated even at 10 EeV.

Detection of weak signals against background (noise) using neural network classifiers

We introduce a new neural classification technique for background rejection in high energy physics and astrophysics experiments, which permits us to (i) directly optimize the desired quantity, i.e. the significance of signal detection (signal to noise ratio); (ii) obtain the complicated nonlinear boundaries for signal event acceptance. Examples of implementing the proposed technique for background rejection in high energy astrophysics experiments are presented.

Observation of Large Deviations from the Bethe-Bloch Formula for Relativistic Uranium Ions

By measuring the range deficit of 955-MeV/u /sup 238/U ions in copper, the authors have identified very large deviations of the stopping power from the standard Bethe-Bloch formula. They show that this discrepancy can be accounted for by higher-order terms in the Mott cross section and by the relativistic Bloch correction. The significance of this result with regard to two high-energy astrophysics experiments is discussed.