Speaker
Description
Ultra-relativistic electrons passing through ordinary matter initiate electromagnetic showers that evolve through bremsstrahlung and pair production. At very high energy, the quantum mechanical duration of bremsstrahlung becomes longer than the mean free time to elastically scatter from the medium, leading to a significant suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. The basic qualitative and quantitative understanding of these processes was seemingly settled in the 1950s, with detailed experimental confirmation in the 1990s. But we find drastic modifications to the LPM bremsstrahlung rate for some regions of extremely high energy bremsstrahlung and electron energies (k, E) where the duration of bremsstrahlung becomes so long that it overlaps subsequent (medium-induced) pair production by the bremsstrahlung photon. Our analysis uses methods originally developed for parton showers in quark-gluon plasmas.