New Feature found in UHECR Energy Spectrum
The energy spectrum of the highest-energy particles in the Universe, ultra-high energy cosmic rays, has been measured with the Pierre Auger Observatory with an unprecedented precision. In addition to the well-known kink in the energy spectrum, typically referred to as the ankle, a new spectral break is found at somewhat higher energy. This new break in the energy spectrum can be explained by an energy-dependent mass composition of cosmic rays. The results are published in two related papers (Phys. Rev. Lett. 125, 121106 (2020) and Phys. Rev. D 102, 062005 (2020)).
This determination of the energy spectrum is unique in having an unprecedented exposure of more than 60,000 km2 sr yr, in its method of determining the spectrum free of assumptions about the mass composition of the initial cosmic ray particle, and about details of the hadronic physics of air showers.