Photon air showers at ultra-high energy and the photonuclear cross-section

Abstract

Experimental conclusions from air shower observations on cosmic-ray photons above 10 19 eV are based on the comparison to detailed shower simulations. For the calculations, the photonuclear cross-section needs to be extrapolated over several orders of magnitude in energy. The uncertainty from the cross-section extrapolation translates into an uncertainty of the predicted shower features for primary photons and, thus, into uncertainties for a possible data interpretation. After briefly reviewing the current status of ultra-high energy photon studies, the impact of the uncertainty of the photonuclear cross-section for shower calculations is investigated. Estimates for the uncertainties in the main shower observables are provided. Photon discrimination is shown to be possible even for rapidly rising crosssections. When photon-initiated showers are identified, it is argued that the sensitivity of photon shower observables to the photonuclear cross-section can in turn be exploited to constrain the cross-section at energies not accessible at colliders. : 96.40.Pq,13.85.Tp PACS

Search for Ultra-High Energy Photons Using Air Showers

“…From simulations with modified cross-sections, uncertainties for photon showers of ∼10 g cm −2 in X max (depth of shower maximum) and ∼15% in N µ (number of muons at ground) were estimated. 70 Assuming an extrapolation such as from Ref. 74 which exceeds the PDG fit by a factor ∼10 at 10 20 eV, a reduction of X max by ∼100 g cm −2 is possible for unconverted photons.…”

Upper limit on the cosmic-ray photon fraction at EeV energies from the Pierre Auger Observatory

“…This shift amounts to $ 7 g cm À2 for a 22% change of the energy scale. Finally, an uncertainty < 10 g cm À2 on the simulated photon X max values comes from the need to extrapolate the photonuclear cross-section to high energy [30]. Adding in quadrature the discussed uncertainties in X max gives an effective total uncertainty of $ 16 g cm À2 .…”

Bounds on length scales of classical spacetime foam models

“…From a highly energetic cosmic-ray event observed on October 15, 1991 by the Fly's Eye Air Shower Detector [37,38], Gagnon and Moore [39] have obtained the following bounds on the quadratic and quartic coefficients of the modified photon dispersion relation [40]:…”