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Direct photon production and PDF fits reloaded
John M Campbell1, Juan Rojo2,3, Emma Slade4
11Fermilab, P.O. Box 500, Batavia, IL 60510 USA.
Direct photon production measurements, including new next-to-next-to-leading order calculations, improve understanding of the gluon parton distribution function (PDF) in hadrons. This analysis refines PDF fits, particularly for medium-x gluons.
Area of Science:
- High-energy particle physics
- Quantum Chromodynamics (QCD)
- Parton distribution functions (PDFs)
Background:
- Direct photon production in hadronic collisions is sensitive to the gluon PDF via QCD Compton scattering.
- Previous analyses were limited by theoretical precision.
Purpose of the Study:
- To reassess the impact of direct photon production on global PDF analyses using recent NNLO calculations.
- To evaluate the constraining power of direct photon data on various PDF fits.
Main Methods:
- Inclusion of NNLO QCD and leading-logarithmic electroweak corrections.
- Global PDF analysis incorporating ATLAS direct photon production data at 8 and 13 TeV.
- Comparison with experimental measurements and assessment of impact on medium-x gluon PDF.
Main Results:
- NNLO calculations achieve good agreement with ATLAS data at 8 and 13 TeV, except at very forward rapidity for 8 TeV.
- Inclusion of ATLAS 8 TeV data in the NNPDF3.1 NNLO analysis impacts the medium-x gluon PDF.
- Direct photon measurements show significant constraining power on PDF fits.
Conclusions:
- Direct photon production at NNLO precision is a valuable probe of the gluon PDF.
- The inclusion of new data and calculations refines our understanding of parton distributions.
- Updated predictions for 13 TeV direct photon production are provided, incorporating 8 TeV constraints.
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