Propagation of muons and taus at high energies

The photonuclear contribution to charged lepton energy loss has been reevaluated taking into account DESY HERA results on real and virtual photon interactions with nucleons. With large Q² processes incorporated, the average muon range in rock for energies of 10⁹ GeV is reduced by only 5% compared with the standard treatment. We have calculated the tau energy loss for energies up to 10⁹ GeV taking into consideration the decay of tau. A Monte Carlo evaluation of tau survival probability and range shows that at energies below 10⁷--10⁸ GeV, depending on the material, only tau decays are important. At higher energies the tau energy losses are significant, reducing the survival probability of the tau. We show that the average range for tau is shorter than its decay length and reduces to 17 km in water for an incident tau energy of 10⁹ GeV, as compared with its decay length of 49 km at that energy. In iron, the average tau range is 4.7 km for the same incident energy.