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A A Watson

Publications and source records attributed to A A Watson.

11 recordsLinked to original sources
arXiv2026

The Development of Detectors of High Energy Neutrinos and Cosmic Rays between 1980 and 2000

The construction of the DUMAND, Lake Baikal and IceCube detectors of high-energy neutrinos are discussed, with some emphasis on the difficulties encountered. The decade from 1990 marked the period in which the Auger Observatory was conceived and the Collaboration evolved. Again, the difficulties that were overcome to create the Observatory are described. For both IceCube and the Auger Observatory, claims made in the 1980s for the observation of PeV gamma-rays from Cygnus X-3, played a not-insignificant role in their advance.

physics.hist-ph↗
arXiv2025

The Mass of Cosmic Rays of Ultra High Energy

A review of several analyses is presented that forces the conclusion that the mass composition of the highest-energy cosmic rays is not proton-dominated. This deduction, combined with the use of a modern hadronic interaction model, should lead to a re-evaluation of the energy spectrum reported by the Telescope Collaboration that may well bring that measurement, and the corresponding one from the Pierre Auger Observatory, into better agreement.

astro-ph.HE↗
arXiv2023

Model-independent Evidence for an Increase in the Mean Mass of Cosmic Rays above 3 EeV

Measurements of the Elongation Rate of the depth of shower maximum above 1 EeV are reviewed. There is evidence, from four independent estimates of this rate, made in the two hemispheres using three different techniques, for a decrease in the Elongation Rate above ~3 EeV, as first discovered by the Pierre Auger Collaboration over 15 year ago. Unless there is a dramatic change in the hadronic physics above this energy, the mean mass of the primary cosmic rays must increase as a function of energy, well into the decade beyond 10 EeV. To estimate the mass, the use of hadronic models is required, the accuracy of which remains uncertain. However, the possibility of a dramatic change in the hadronic physics appears unlikely, and would be inconsistent with data from the Auger Collaboration on the mass composition in the range 3 to 10 EeV, and on the anisotropy of arrival directions above 8 EeV. Both of these conclusions are insensitive to uncertainties in the shower models. Some remarks are made about the belief, still firmly held by some, that the highest-energy cosmic rays are dominantly protons.

astro-ph.HE↗
arXiv2021

Further Evidence for an Increase of the Mean Mass of the Highest-Energy Cosmic-Rays with Energy

Sokolsky and D_Avignon have recently reported an examination of a variety of measurements that relate to the question as to how the mass composition of the highest-energy cosmic-rays evolves with energy. They assert that cosmic rays arriving from the Northern Hemisphere have a different mass composition from those arriving from the Southern Hemisphere, implying a diversity of sources of high-energy cosmic-rays in the two hemispheres. Were this conclusion to be correct, it would have profound implications for theories of cosmic-ray origin and would influence planning of future projects. Their claim thus merits careful scrutiny. In this paper their analysis is examined in detail with the verdict being that evidence for a North/South difference is not proven, a conclusion supported by other data from the Northern and Southern Hemispheres. However, what is of major importance is that the study of Sokolsky and D_Avignon provides long-awaited confirmation of the claim that the mean mass of cosmic rays increases with energy above ~3 E eV made by the Pierre Auger Collaboration in 2014.

astro-ph.HE↗
arXiv2019

The Origins of the Highest Energy Particles in Nature: where we are and where we go next

In his Nobel Prize lecture Victor Hess urged that different instruments, working together, should be used to solve the problem of the origin of cosmic rays. I review some of the key developments that have opened up the new fields of direct and indirect multi-messenger astronomy and that are guiding us to the solution of this riddle. I then discuss, very briefly, some of the new instruments that are shortly to come on line and give examples to show the long lead-times from conception to implementation that occur in this field. I conclude with some remarks about very ambitious future projects. The paper is not intended as a review: rather it is an attempt to set down issues discussed in the Hess Memorial Public Lecture given at the 2019 ICRC in Madison, Wisconsin and accessible at www.icrc2019.org.

astro-ph.IM↗
arXiv2019

The highest energy cosmic rays: the past, the present and the future

The greater part of this paper is concerned with a historical discussion of the development of the search for the origins of the highest-energy cosmic-rays together with a few remarks about future prospects. Additionally, in section 6, the situation with regard to the mass composition and energy spectrum at the highest energies is discussed. It is shown that the change of the depth of shower maximum with energy above 1 EeV, measured using the Telescope Array, is in striking agreement with similar results from the Auger Observatory. This implies that either the mean mass of cosmic rays is becoming heavier above ~4 EeV or that there is a change in details of the hadronic interactions in a manner such that protons masquerade as heavier nuclei. A long-standing controversy is thus resolved: the belief that pure protons dominate the mass distribution at the highest energies is no longer tenable.

astro-ph.IM↗
arXiv2016

Conclusions about properties of high-energy cosmic-rays drawn with limited recourse to hadronic models

Determining the energy and mass of the highest energy cosmic rays requires knowledge of features of particle interactions at energies beyond those reached at the LHC. Inadequacies of the model predictions set against a variety of data are summarised and it is clear that firm statements about primary mass are premature. Nonetheless, conclusions of significance about the origin of the highest-energy cosmic rays can be deduced from the data. This paper is dedicated to my great friend and colleague, Jim Cronin, who died suddenly on 25 August 2016, without whom the Auger Collaboration would not have happened.

astro-ph.HE↗
arXiv2013

High-Energy Cosmic Rays and the Greisen-Zatsepin-Kuzmin Effect

Although cosmic rays were discovered over 100 years ago their origin remains uncertain. They have an energy spectrum that extends from 1 GeV to beyond 1020 eV, where the rate is less than 1 particle per km2 per century. Shortly after the discovery of the cosmic microwave background in 1965, it was pointed out that the spectrum of cosmic rays should steepen fairly abruptly above about 4 x 1019 eV, provided the sources are distributed uniformly throughout the Universe. This prediction, by Greisen and by Zatsepin and Kuzmin, has become known as the GZK-effect and in this article I discuss the current position with regard to experimental data on the energy spectrum of the highest cosmic-ray energies that have been accumulated in a search that has lasted nearly 50 years. Although there is now little doubt that a suppression of the spectrum exists near the energy predicted, it is by no means certain that this is a manifestation of the GZK-effect as it might be that this energy is also close to the maximum to which sources can accelerate particles, with the highest-energy beam containing a large fraction of nuclei heavier than protons. The way forward is briefly mentioned.

astro-ph.HE↗
arXiv2011

The Discovery of Cherenkov Radiation and its use in the detection of extensive air showers

Cascades of charged particles are created when high-energy cosmic rays enter the earth's atmosphere: these 'extensive air-showers' are studied to gain information on the energy spectrum, arrival direction distribution and mass composition of the particles above 1014 eV where direct observations using instruments carried by balloons or satellites become impractical. Detection of light in the visible and ultra-violet ranges of the electromagnetic spectrum plays a key role in this work, the two processes involved being the emission of Cherenkov light and the production of fluorescence radiation. In this paper I will outline some of the history of the discovery of the Cherenkov process and describe the use to which it has been put in the study of extensive air-showers at ground level.

physics.hist-ph↗
arXiv2005

Observations of Ultra-High Energy Cosmic Rays

The status of measurements of the arrival directions, mass composition and energy spectrum of cosmic rays above 3 x 10^18 eV (3 EeV) is reviewed using reports presented at the 29th International Cosmic Ray Conference held in Pune, India, in August 2005. The paper is based on a plenary talk given at the TAUP2005 meeting in Zaragoza, 10 - 14 September 2005.

astro-ph↗