2005/01/18 by H. J. Drescher, Adrian Dumitru, A. Dumitru +4
Physics and Astronomy · #Astrophysics (astro-ph) #Astrophysics and Cosmic Phenomena #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #astro-ph #hep-ph
paper · pdf · doi:10.48550/arxiv.hep-ph/0501165
To appear in the proceedings of the 44th INFN Workshop, "QCD at Cosmic Energies", Aug.29 - Sept.5, 2004, Erice, Italy
arxiv created 2005/01/18 · openalex publication_date 2005/01/18 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We discuss that hadron-induced atmospheric air showers from ultra-high energy cosmic rays are sensitive to QCD interactions at very small momentum fractions x where nonlinear effects should become important. The leading partons from the projectile acquire large random transverse momenta as they pass through the strong field of the target nucleus, which breaks up their coherence. This leads to a steeper xF-distribution of leading hadrons as compared to low energy collisions, which in turn reduces the position of the shower maximum Xmax. We argue that high-energy hadronic interaction models should account for this effect, caused by the approach to the black-body limit, which may shift fits of the composition of the cosmic ray spectrum near the GZK cutoff towards lighter elements. We further show that present data on Xmax(E) exclude that the rapid ~ 1/x0.3 growth of the saturation boundary (which is compatible with RHIC and HERA data) persists up to GZK cutoff energies. Measurements of pA collisions at LHC could further test the small-x regime and advance our understanding of high density QCD significantly.