The Pierre Auger Observatory is the largest Cosmic Ray detector in the world. It has brought new fundamental insights about the origin and nature of highest-energy cosmic rays. One of the most exciting results is the experimental proof that at the highest energies the cosmic-ray flux is strongly suppressed. However, the mechanism responsible for the suppression is still a subject of debate: are we observing the result of the GZK mechanism, by which the energy of cosmic rays is degraded by their interaction with cosmic microwave background photons in their voyage to Earth, or the exhaustion of cosmic sources? Concerning composition, extensive air shower parameters seem to favour heavy composition, whereas the existence of anisotropies favours a light primary. However, the interactions of ultra high energy cosmic rays with Earth’s atmosphere are still poorly understood, and current measurements of the produced air showers aren’t able to shed light in a myriad of aspects of these interactions.

The Pierre Auger Collaboration is performing an upgrade of the full array and expects to take data at least until 2025. Scintillators are being installed on top of every water Cherenkov detector, the the electronics is being upgrades to a faster one. The aim is to achieve a better knowledge of the different components of air showers. A great effort is being put in the development of next-generation data analyses and hadronic interaction models to attain a good description of showers. The muonic component of the shower plays a particularly important role, as it can probe directly the early stages of the shower development. However, muons are only indirectly accessible even with the upgraded detector, with refined analysis required to separate them from the dominant electromagnetic signals.

A small part of the Auger array will be equipped with additional detectors that will allow for calibration and detailed response studies of the full array. In the last years the LIP team has been deeply involved in the development of the MARTA project, a joint Portugal-Brazil effort to measure directly the muon content at the shower using resistive plate chamber detectors (RPCs) installed beneath the water Cherenkov detectors. Low gas flux RPCs, able to work on a harsh outdoor environment with very little maintenance, were developed at LIP in Coimbra and built in cooperation with São Carlos, Brazil.  The LIP team has also acquired a deep knowledge in shower physics and has developed innovative analyses methods and tools that will allow us to give important contributions in the analysis of the new Auger data.

Group webpage at LIP