Abstract
The prompt photon production in hadronic collisions has a long history of providing information on the substructure of hadrons and testing the perturbative techniques of QCD. Some valuable information about the parton densities in the nucleon and nuclei, especially of the gluon, can also be achieved by analysing the measurements of the prompt photon production cross section whether inclusively or in association with heavy quarks or jets. In this work, we present predictions for the inclusive isolated prompt photon production in pp collisions at center-of-mass energy of 13 TeV using various modern PDF sets. The calculations are presented as a function of both photon transverse energyETγand pseudorapidityηγfor the ATLAS kinematic coverage. We also study in detail the theoretical uncertainty in the cross sections due to the variation of the renormalization, factorization, and fragmentation scales. Moreover, we introduce and calculate the ratios of photon momenta for different rapidity regions and study the impact of various input PDFs on such quantity.
Highlights
“prompt photons” are those photons that come from the collision of two primary partons in the protons, that is, photons not originating from hadron decays. The study of such photons provides a probe of perturbative Quantum Chromodynamics and measurement of their production cross sections, because of the sensitivity of the process to the gluon content of the nucleon, can provide useful information about the gluon parton distribution function (PDF) [45,46,47,48,49]
In [48] the authors found a small effect on the gluon density due to the inclusion of large number of isolated prompt photon production data until 2012 related to the various experiments at different center-of-mass energies in a global analysis of PDFs, it is expected that the recent ATLAS data [16] measured at center-of-mass energy √s = 8 TeV can be used to improve PDF fits especially at larger Bjorken scaling variable x where the PDF uncertainties are relatively large [35]
Theoretical and computational aspects of the inclusive isolated prompt photon production such as involved leading order (LO) and next-to-leading order (NLO) subprocesses, direct and fragmentation component of the cross section, and photon isolation requirement have been discussed in many papers
Summary
Prompt photon production at hadron colliders has undergone very impressive experimental [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18] and theoretical [19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41] developments. In [48] the authors found a small effect on the gluon density due to the inclusion of large number of isolated prompt photon production data until 2012 related to the various experiments at different center-of-mass energies in a global analysis of PDFs, it is expected that the recent ATLAS data [16] measured at center-of-mass energy √s = 8 TeV can be used to improve PDF fits especially at larger Bjorken scaling variable x where the PDF uncertainties are relatively large [35].
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