Pierre Auger Observatory

Hybrid Detector

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The hybrid nature of the Pierre Auger Observatory provides for two independent ways to see cosmic rays. Read More...

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Who Was Pierre Auger?

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The Pierre Auger Observatory experiment was named after Pierre Victor Auger (1899 - 1993) Read More...

James W. Cronin – Founding Father of the Pierre Auger Observatory, 1931-2016


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James W. Cronin (University of Chicago)


The Pierre Auger Collaboration sadly shares the news that James W. Cronin, Professor Emeritus at the University of Chicago and spokesperson emeritus of Auger died on 25 August, at the age of 84.

Born in Chicago, Illinois, on 29 September 1931, graduated with a PhD in physics in 1955, James Cronin shared the 1980 Nobel Prize for Physics with Val Fitch for their 1964 discovery that decaying subatomic particles called K mesons violate a fundamental principle in physics known as "CP symmetry."

After his prizewinning work, he eventually turned his research to cosmic rays and he was a founding father of the Pierre Auger Observatory, the world's largest cosmic-ray detector, which he conceptualized in 1992 with fellow physicist from the University of Leeds Alan Watson.

In his Nobel biographical statement, he emphasized the importance of his family to his career. “On even the worst days, when nothing was working at the lab, I knew that at home I would find warmth, peace, companionship, and encouragement. As a consequence, the next day would surely be better.”

Our thoughts and deepest sympathy go to his family, his wife, children and grandchildren.

How it all began

In August 1991 at the Dublin ICRC, Jim Cronin and Alan Watson first started talking about building a giant array. So that marks a significant anniversary in the history of the Pierre Auger Observatory – 25 years!

10 years ago Alan Watson wrote an article (based on an oral presentation made at a meeting in Chicago to honour Jim Cronin on his 75th birthday in September 2006!) describing the birth of the project.


Humberto Salazar Ibarguen receives "Luis Rivera Terrazas" medal in Puebla

Humberto Salazar Ibarguen, researcher at the Faculty of Physical and Mathematical Sciences of the Benemérita Universidad Autónoma de Puebla (BUAP) in Mexico, received the medal of Science and Technology "Luis Rivera Terrazas" in recognition of his contributions in the field of Natural Sciences.


AugerPrime featured in the June 2016 issue of the CERN Courier

The planned upgrade of the Pierre Auger Observatory, AugerPrime, is featured as the cover story in the June 2016 issue of the CERN Courier,  an international journal of high-energy physics whose readership spans the globe. The article, titled “AugerPrime looks to the highest energies”, explains the scientific motivation for the detector upgrades and presents some of the improvements foreseen to enhance the experiment’s performance. AugerPrime is expected to be completed in 2018 with little interruption to current data-taking operations.


The energy in the radio signal of extensive air showers - a universal estimator for the cosmic-ray energy

One of the biggest challenges in cosmic-ray physics is to accurately pin down the absolute energy of a measured cosmic ray. This is traditionally done with an array of particle detectors deployed on a large grid, which then sample the energetic "air-shower" particles made in atmospheric interactions of the original cosmic particle. This is a tough challenge for particle detectors because the complex interaction physics at the highest energies has to be extrapolated from measurements at collider experiments, which operate at significantly lower energies - even at the Large Hadron Collider (LHC). To accurately set the absolute energy scale, scientists using the Pierre Auger Observatory thus rely on combining the particle detectors (for Auger, water tanks used to measure the Cherenkov light flash made in the water by relativistic charged particles) with the nitrogen fluorescence detection technique. This works very well, but requires tremendous effort, in particular to control the effects of scattering and absorption in the ever-changing atmosphere. Now, we have shown that radio detection of extensive air showers can be a very powerful means to cross-calibrate the absolute energy scale of different experiments.


Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger Observatory

Billions of subatomic particles can be created in cosmic-ray induced air showers. They travel at nearly the speed of light through the atmosphere, and eventually through the surface detector water tanks of the Pierre Auger Observatory, deployed over 3000 km2 of the Argentine pampas. Because of their relativistic speed, when propagating in the water they generate a flash of so-called Cherenkov light, the same phenomenon that causes the bluish glow in a water pool of radioactive material. The light flash is faint and requires specialized electronic light sensors (photomultiplier tubes) that can detect the intensity of the light and its time structure. For example the "risetime" is measured: this is the time that it takes for the light generated to go from 10% to 50% of the total in the overall Cherenkov flash. This time is very short, of the order of a few hundred nanoseconds, thus the need for the specialized photomultiplier sensors.


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Auger On Site

Shower Simulations

shower simulation

A computer is used to construct a model of what happens in a high energy cosmic ray airshower. Read More...

Google Earth


A model of the Observatory layout was constructed, to be viewed interactively using Google Earth. Read More...

Event Display


The Pierre Auger Collaboration agreed on making 1% of its data available to the public. Read More...