Rare processes in ultrahigh-energy tau-lepton transport

In cosmic neutrino observatories, charged-lepton transport is a key input for interpreting observables and reconstructing neutrino events. Charged leptons propagating through matter undergo several energy loss processes, such as electron pair production and photonuclear interaction. In this work, we investigate several rare processes in tau-lepton transport, focusing primarily on muon pair production, τ N → τ μ⁺μ⁻ N, and Primakoff neutral-pion production, τ N → τ π⁰ N. At EeV energies, we find that the energy loss contributions from muon pair and Primakoff pion production are only $0.6%$ and $0.2%$, respectively, of that from electron pair production. Nevertheless, dimuon production may be relevant to tau neutrino searches in underwater and under-ice Cherenkov telescopes. The interaction length for dimuon emission by an EeV tau is only 6~ km in standard rock. Such events may be identified through the lateral separation of dimuon tracks or through a kebab topology if tau decays in the detector. In addition, we also emphasize that hard photonuclear scatterings during tau transport become increasingly important at the energy scales relevant for lunar neutrino searches like SKA-Low. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.