The Pierre Auger Observatory measures the longitudinal air shower profile of ultra high energy cosmic rays which gives information on composition and hadronic interaction properties. Eun-Joo Ahn and colleagues use this data to obtain the proton-air cross section. Preliminary results show a surprising rise in the cross section with energy, which is not predicted by current hadronic interaction models. This is a hint of new physics at energies inaccessible to the LHC. More data from Auger is expected to resolve the issue.
– Eun-joo Ahn