- What Are Cosmic Rays?
Pictorial representation of a cosmic ray shower over the Auger Observatory, triggering some of its ground detectors.
Cosmic rays are protons and other atomic nuclei possessing enormous energies. The rarest have energies almost 100 million times greater than protons accelerated by the Large Hadron Collider (LHC), and represent the most energetic particles known in the Universe.
Astrophysicists have been striving to understand how and where Nature accelerates these particles to such extreme energies, and how they fit with the broader astrophysical picture.
The giant Pierre Auger Observatory , covering 3000 square kilometres in western Argentina, has made great strides towards solving these long-standing and important astrophysical problems.
- How Do We Detect Cosmic Rays?
In the foreground is one of the Auger ground tanks for detecting cosmic ray showers. In the distance, on top of the hill, is one of the nitrogen fluorescence detector stations.
Extremely energetic cosmic rays initiate enormous cascades of secondary particles when they strike the Earth's atmosphere. Such an air shower can cover tens of square kilometres at ground level, and during its passage through the atmosphere the shower induces a flash of bluish fluorescence light.
The Pierre Auger Observatory observes the showers in two complementary ways to extract information on the nature of the incoming cosmic rays, including their energy, arrival direction and mass.
An array of 1660 particle detectors spread over 3000 square kilometres measures the shower particles as they strike Earth, while a series of 27 large optical telescopes measures the flashes of light from atmospheric nitrogen excited by the shower.
The cascade of particles in an air shower, looking down along its path towards the ground.
Since full operations began in 2008, the Pierre Auger Observatory has exploited the sensitivity and size of the Observatory to publish many studies on the characteristics of the high-energy cosmic ray flux, including a high-statistics measurement of the suppression of the flux at the highest energies, strong limits on the photon and neutrino content, intriguing indications of large- and small-scale clustering of arrival directions, and an interpretation of air shower measurements indicating an increase in the average mass of the cosmic ray particles at the highest energies.
At the same time, high-energy particle interactions have been studied at energies inaccessible to man-made particle accelerators. A major upgrade of the Observatory commenced in 2016 to enhance the sensitivity of the surface array detectors to the mass of the cosmic ray particles.
- What Do We Do at HEAG?
The University of Adelaide hosts one of the largest groups in the Auger collaboration. Adelaide was a founding member of the collaboration, and hosted its first design workshop in 1993. Members of the Adelaide group now hold key positions in the collaboration, including leadership roles in the Mass Composition and Analysis Foundations tasks, and in the Upgrade Task Force.
Staff and students undertake tasks including development of hardware and software to assist with data analysis, as well as taking part in observing runs and interpretation of results.