M. Ave et al., New constraints from Haverah Park data on the photon and iron fluxes of ultrahigh-energy cosmic rays, PHYS REV L, 85(11), 2000, pp. 2244-2247
Using data from inclined events (60 degrees < theta < 80 degrees) recorded
by the Haverah Park shower detector, we show that above 10(19) eV less than
41% (54%) of the primary cosmic rays can be photons (iron nuclei) at the 9
5% confidence level. Above 4 x 10(19) eV less than 65% of the cosmic rays c
an be photonic at the same confidence level. These limits place important c
onstraints on some models of the origin of ultrahigh-energy cosmic rays. De
tails of two new events above 10(20) eV are reported.