Campbell John M, Rojo Juan, Slade Emma, Williams Ciaran
1Fermilab, P.O. Box 500, Batavia, IL 60510 USA.
2Department of Physics and Astronomy, VU University, 1081 HV Amsterdam, The Netherlands.
Eur Phys J C Part Fields. 2018;78(6):470. doi: 10.1140/epjc/s10052-018-5944-4. Epub 2018 Jun 9.
Direct photon production in hadronic collisions provides a handle on the gluon PDF by means of the QCD Compton scattering process. In this work we revisit the impact of direct photon production on a global PDF analysis, motivated by the recent availability of the next-to-next-to-leading (NNLO) calculation for this process. We demonstrate that the inclusion of NNLO QCD and leading-logarithmic electroweak corrections leads to a good quantitative agreement with the ATLAS measurements at 8 and 13 TeV, except for the most forward rapidity region in the former case. By including the ATLAS 8 TeV direct photon production data in the NNPDF3.1 NNLO global analysis, we assess its impact on the medium- gluon. We also study the constraining power of the direct photon production measurements on PDF fits based on different datasets, in particular on the NNPDF3.1 no-LHC and collider-only fits. We also present updated NNLO theoretical predictions for direct photon production at 13 TeV that include the constraints from the 8 TeV measurements.
强子碰撞中的直接光子产生通过量子色动力学（QCD）康普顿散射过程为胶子部分子分布函数（PDF）提供了一种研究途径。在这项工作中，鉴于该过程的次下一个领先阶（NNLO）计算的最新可得性，我们重新审视直接光子产生对全局PDF分析的影响。我们证明，纳入NNLO QCD和领先对数电弱修正后，与8 TeV和13 TeV时ATLAS的测量结果在定量上吻合良好，但在前一种情况的最前向快度区域除外。通过在NNPDF3.1 NNLO全局分析中纳入ATLAS 8 TeV直接光子产生数据，我们评估其对中等x胶子的影响。我们还研究了基于不同数据集的直接光子产生测量对PDF拟合的约束能力，特别是对NNPDF3.1无LHC和仅对撞机拟合的约束能力。我们还给出了13 TeV时直接光子产生的更新后的NNLO理论预测，其中包括来自8 TeV测量的约束。
