Abstract
The basic expressions for the differential nuclear bremsstrahlung cross section at high electron energy, as derived under different theoretical approaches and approximations to quantum coherence effects, are compared. The Baier-Katkov treatment is reformulated to allow introduction of the same value of the radiation length in all calculations. A dedicated Monte Carlo code is employed for obtaining photon energy spectra in the framework of the Baier-Katkov approach taking into account multiphoton emission, attenuation by pair production, and pile-up with photons from the background. The results of Monte Carlo simulations for both the Migdal and Baier-Katkov descriptions are compared to all available data that show the Landau-Pomeranchuk-Migdal suppression. The issue of the sensitivity of the experiments to the difference of the two approaches is investigated.
Highlights
Ever since the pioneering papers by Sauter [1], Bethe and Heitler [2,3], and Racah [4], the bremsstrahlung process undergone by electrons and positrons in crossing matter has attracted the interest of theorists and experimentalists
A dedicated Monte Carlo code is employed for obtaining photon energy spectra in the framework of the Baier-Katkov approach taking into account multiphoton emission, attenuation by pair production, and pile-up with photons from the background
The most important expressions that different authors proposed over the years to account for bremsstrahlung at high energies are described in the following with particular focus on those that take into account quantum coherence effects
Summary
Ever since the pioneering papers by Sauter [1], Bethe and Heitler [2,3], and Racah [4], the bremsstrahlung process undergone by electrons and positrons in crossing matter has attracted the interest of theorists and experimentalists. One of the most important steps forward in the theory was the recognition by Landau and Pomeranchuk [5,6] of the possible suppression of the intensity of the bremsstrahlung radiation due to a reduction of the coherence length caused by the multiple scattering suffered by the radiating particle These authors used pure classical arguments, while Migdal [7] developed a fully quantum-mechanical theory of the bremsstrahlung process including the mentioned suppression. Important motivations to improve as far as possible the basic electromagnetic cross sections under strong LPM suppression, used in simulations, derive from the recent opening of PeV gamma ray astronomy [34,35] and the present differences between experiments in the measured electron and positron primary cosmic ray fluxes in the TeV region [36,37].
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