A new approach to inferring the mass composition of cosmic rays

We describe a new approach to establishing the mass composition at high energies. Based on measuring both the vertical and inclined shower rates, it has the potential to distinguish heavy nuclei from light nuclei. We apply the method to Haverah Park data above 1018 eV, under the assumption that the Quark Gluon String Jet Model correctly describes the high-energy interactions. Our conclusions depend on the assumed initial flux spectrum: they are thus preliminary. To the extent that precise spectral measurements will be possible by forthcoming experiments such as the Auger observatories, and that further data will constrain the models that might be possible, the method will have an important role in establishing the mass composition of the ultra-high-energy cosmic rays.