Direct photon production with effective field theory

TL;DR

This paper applies Soft-Collinear Effective Theory to compute the direct photon production cross section in hadronic collisions, achieving higher precision and reduced theoretical uncertainties compared to previous methods.

Contribution

It is the first application of SCET to a physical cross section with multiple energetic partons, deriving a NNLL resummed distribution including non-logarithmic terms and comparisons with experimental data.

Findings

Resummed cross section has smaller theoretical uncertainty.

Results agree well with Tevatron and LHC data.

Achieved NNLL accuracy beyond previous work.

Abstract

The production of hard photons in hadronic collisions is studied using Soft-Collinear Effective Theory (SCET). This is the first application of SCET to a physical, observable cross section involving energetic partons in more than two directions. A factorization formula is derived which involves a non-trivial interplay of the angular dependence in the hard and soft functions, both quark and gluon jet functions, and multiple partonic channels. The relevant hard, jet and soft functions are computed to one loop and their anomalous dimensions are determined to three loops. The final resummed inclusive direct photon distribution is valid to next-to-next-to-leading logarithmic order (NNLL), one order beyond previous work. The result is improved by including non-logarithmic terms and photon isolation cuts through matching, and compared to Tevatron data and to fixed order results at the Tevatron and the LHC. The resummed cross section has a significantly smaller theoretical uncertainty than the next-to-leading fixed-order result, particularly at high transverse momentum.