Pierre Auger Observatory

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.

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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.

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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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