Measurement of photon production cross sections also in association with jets with the ATLAS detector

Sebastien Prince

doi:10.1016/j.nuclphysbps.2018.03.016

Abstract

The production of prompt isolated photons at hadron colliders provides a stringent test of perturbative QCD and can be used to probe the proton structure. The production of prompt photons in association with jets provides an additional testing ground for perturbative QCD with a hard colourless probe less affected by hadronisation effects than jet production. At the LHC, the ATLAS collaboration has performed precise measurements of the inclusive production of isolated prompt photons at a centre-of-mass energy of 13 TeV. The dynamics of isolated-photon plus jet production in pp collisions at a centre-of-mass energy of 8 TeV have also been measured. In addition, the integrated and differential cross sections for isolated photon pairs at a centre-of-mass energy of 8 TeV have been measured. The results are compared with state-of-the art theory predictions at next-to-leading order in perturbative QCD.

Highlights

Prompt photons are interesting objects to measure at the LHC since they test perturbative QCD in a unique way
For LO photon production associated with jets, the main diagrams are Compton scattering, gq → γq, and quark-antiquark annihilation, qq → γg
A smaller contribution is the next-tonext-to-leading order (NNLO) in perturbative QCD (pQCD) quark box diagram, gg → γγ, which is enhanced by the large gluon parton distribution functions (PDFs) of the proton

Summary

Introduction

Prompt photons are interesting objects to measure at the LHC since they test perturbative QCD (pQCD) in a unique way. They are less affected by hadronisation effects than jets are, while still being relatively abundant As their main production mechanism is through Compton scattering, i.e. through an interaction with the quarks inside the proton, their measurement can help constrain parton distribution functions (PDFs) of the proton. A smaller contribution is the next-tonext-to-leading order (NNLO) in pQCD quark box diagram, gg → γγ, which is enhanced by the large gluon PDF of the proton For both photon plus jet and diphoton production, prompt photons can be produced. / Nuclear and Particle Physics Proceedings 00 (2017) 1–6 as initial- or final-state radiation These are formally next-to-leading order (NLO) diagrams, in the collinear limit of the photon being produced close to the parton, non-perturbative fragmentation functions are necessary to avoid divergences. For differential cross sections binned as function of an observable, an extra step is done relative to equation 1: dividing by the bin width of the observable

Inclusive photon production at 13 TeV

Diphoton production at 8 TeV

Conclusion