New physics, the cosmic ray spectrum knee, and $pp$ cross section measurements

TL;DR

This paper investigates whether new physics interactions could explain the cosmic ray spectrum knee by modeling modifications to the proton-proton cross section and fitting cosmic ray data, with implications for collider experiments.

Contribution

It introduces a model for new physics effects on the proton-proton cross section that can account for the cosmic ray knee and fits cosmic ray flux data, suggesting a black disc scattering regime at high energies.

Findings

Significant rise in cross section above the knee energy

Good fit to Tibet III cosmic ray flux data

Potential for testing at the Large Hadron Collider

Abstract

We explore the possibility that a new physics interaction can provide an explanation for the knee just above $10^6$ GeV in the cosmic ray spectrum. We model the new physics modifications to the total proton-proton cross section with an incoherent term that allows for missing energy above the scale of new physics. We add the constraint that the new physics must also be consistent with published $pp$ cross section measurements, using cosmic ray observations, an order of magnitude and more above the knee. We find that the rise in cross section required at energies above the knee is radical. The increase in cross section suggests that it may be more appropriate to treat the scattering process in the black disc limit at such high energies. In this case there may be no clean separation between the standard model and new physics contributions to the total cross section. We model the missing energy in this limit and find a good fit to the Tibet III cosmic ray flux data. We comment on testing the new physics proposal for the cosmic ray knee at the Large Hadron Collider.