Proton-Proton to Antinucleon Cross Sections for Cosmic Ray Applications

TL;DR

This paper predicts antiproton and antineutron production cross sections in proton-proton collisions relevant to cosmic ray physics, using QCD calculations and analyzing experimental data uncertainties.

Contribution

It provides next-to-leading order QCD predictions for antinucleon production and critically evaluates experimental claims of antineutron excess in cosmic ray interactions.

Findings

Predictions do not support the ~30% antineutron excess reported by NA49.

Results indicate a mild, a few percent, excess of antineutrons over antiprotons.

Reconciliation of NA49 results with predictions requires large differences in low transverse momentum production.

Abstract

We present predictions of inclusive antiproton and antineutron production cross sections in proton-proton collisions relevant to primary and secondary antiproton production in cosmic ray interactions with interstellar matter. Our predictions are based on collinear factorisation in Quantum Chromodynamics and are accurate to next-to-leading order in the perturbative expansion of the strong coupling. We assess the relevance of cross sections measured at collider experiments, such as NA49 at the CERN SPS and ALICE at the LHC, to the kinetic energy ranges accessed by cosmic ray detectors. We characterise the associated uncertainties due to the input parton distribution and fragmentation functions, and to missing higher orders. We critically examine the ~30% excess of antineutron over antiproton production in proton-proton collisions preliminarily reported by the NA49 experiment by combining our predictions with a data-driven model. Our results do not support the NA49 finding, and point to a mild excess of a few percent. We finally show that the NA49 result could only be reconciled with our framework by invoking sizeable differences between antiproton and antineutron production in the poorly constrained region of small transverse momenta of the produced hadron.