Hadronic interactions at ultra-high energy

Felix Riehn

Ultra-high energy cosmic rays (UHECR) are the most energetic particles observed in nature. As such they provide a unique view to the universe at its most extreme. In recent years there have been indications that something unexpected may be happening in the interactions of the UHECRs in the atmosphere. Namely it was found that the number of muons which are produced in extensive air showers is much larger than what is expected based. In this presentation I will briefly discuss these observations, what they imply about the nature of particle interactions at the highest energies and how they are connected to the LHC.