Speaker
Description
For 20 years the Pierre Auger Observatory is measuring ultra-high energy cosmic rays. Among the early discoveries was the confirmation of a strong suppression of the flux of cosmic rays at energies beyond 10EeV. If cosmic rays were mostly protons of extragalactic origin, as it was supposed, such a suppression is expected from the absorption of cosmic rays in the CMB. However, subsequent measurements of the mass of cosmic rays revealed the presence of heavy nuclei in the flux. While a flux purely composed of protons is ruled out, studies of the arrival directions have recently delivered strong evidence for the extragalactic origin and some evidence for a correlation with star-burst-galaxies. The picture that is emerging is thus of a complex and nuanced universe at the highest energies. But what if ... ?
What if the interpretation of the mass measurements is askew because we fail to account for a new aspect in the interactions of the cosmic rays with the atmosphere? After all the energy scale of ultra-high energy cosmic rays is an order of magnitude larger than the energies probed at the LHC. Indeed, measurements of the average muon content of air showers induced by ultra-high energy cosmic rays, a quantity that is closely linked to the hadronic activity in the shower, reveal a curious discrepancy when comparing to expectations from theory. Could this muon excess be the telltale sign of new physics? Does the picture of ultra-high energy cosmic rays have to be revised yet again?
In this presentation the measurements by the Pierre Auger Observatory that led to the current picture of ultra-high energy cosmic rays will be introduced. Particular focus is put on measurements of muons in air showers and how these fit in the current picture and why the scenario of new physics is disfavored.
| Topic | Detectors and new facilities |
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