Particle theory

Abstract:

We present the two-loop QCD amplitudes for the production of two photons and a jet at hadron colliders with full-color dependence. This is the first time that radiative corrections for a five-particle scattering process have been computed beyond the leading-color approximation at this perturbative order in QCD. The results presented in this Letter will be crucial to guaranteeing reliable predictions with unprecedented precision for diphoton production at hadron colliders. The methodologies that we describe lead to a significant simplification of the calculation and their applicability extends to a wider range of five-point scattering processes.

Abstract:

Despite significant efforts over the past decade, the origin of the cosmic ray positron excess has still not been unambiguously established. A popular class of candidate sources are pulsars or pulsar wind nebulae but these cannot also account for the observed hard spectrum of cosmic ray antiprotons. We revisit the alternative possibility that the observed high-energy positrons are secondaries created by spallation in supernova remnants during the diffusive shock acceleration of the primary cosmic rays, which are further accelerated by the same shocks. The resulting source spectrum of positrons at high energies is then naturally harder than that of the primaries, as is the spectrum of other secondaries such as antiprotons. We present the first comprehensive investigation of the full parameter space of this model—both the source parameters as well as those governing galactic transport. Various parametrizations of the cross sections for the production of positrons and antiprotons are considered, and the uncertainty in the model parameters discussed. We obtain an excellent fit to recent precision measurements by AMS-02 of cosmic ray protons, helium, positrons, and antiprotons, as well as of various primary and secondary nuclei. This model thus provides an economical explanation of the spectra of all secondary species—from a single well-motivated population of sources.