MSHT Approximate N3LO PDFs: Updates and Consequences for Phenomenology
T. Cridge, L. A. Harland-Lang, R. S. Thorne
备注：
10 pages, 3 figures. Talk presented at the XXXII International Workshop on Deep Inelastic Scattering and Related Subjects (DIS 2025), Capetown, South Africa, 24-28 March 2025. To appear in the proceedings
We present updates to the MSHT approximate N3LO PDFs focusing upon recent developments, examining the impacts of newly determined splitting function and transition matrix element calculations, performed since the public MSHT20aN3LO PDF set was released. We observe only small changes to the output PDFs, at most of similar size to their quoted uncertainties and typically notably less. Finally, we also present the impacts on the PDF luminosities, where changes are generally further reduced.
There have been recent updates to the three global PDF fits (CT, MSHT and NNPDF), all adding large amounts of data from the LHC, and this has resulted in significant changes to the global PDFs. Given the impact that the new PDFs will have on physics comparisons at the LHC, it is crucial to perform a benchmarking among the PDFs, similar in spirit to that which was carried out for PDF4LHC15, widely used for LHC physics. In this article we detail a benchmarking comparison of three global PDF sets - CT18, MSHT20 and NNPDF3.1 - and their similarities and differences that have been observed. The end…
We present the first global analysis of parton distribution functions (PDFs) at approximate N$^{3}$LO in the strong coupling constant $α_{s}$, extending beyond the current highest NNLO achieved in PDF fits. To achieve this, we present a general formalism for the inclusion of theoretical uncertainties associated with the perturbative expansion in the strong coupling. We demonstrate how using the currently available knowledge surrounding the next highest order (N$^{3}$LO) in $α_{s}$ can provide consistent, justifiable and explainable approximate N$^{3}$LO (aN$^{3}$LO) PDFs. This includes estimat…
We present the MSHT20qed set of parton distribution functions (PDFs). These are obtained from the MSHT20 global analysis via a refit including QED corrections to the DGLAP evolution at ${\cal O}(α),{\cal O}(αα_S)$ and ${\cal O}(α^2)$, and containing the photon PDF of the proton. As in the previous MMHT15qed study we use an input distribution for the photon that is derived from the LUXqed formulation, and find good consistency for the photon PDF with that of MMHT15qed, as well as with other recent sets. We also present a set of QED corrected neutron PDFs and accompanying photon distribution, an…
Phenomenology of diffractive DIS in the framework of fracture functions and determination of diffractive parton distribution functions
本研究的目的是确定一组衍射部分子分布函数（衍射PDF）的QCD分析所有可用的和最新的衍射深度非弹性散射（DIS）数据集从HERA $ep$对撞机，包括最新的H1和ZUES相结合的包容性衍射截面测量。这种衍射PDF的提取被称为{ \tt HK 19-DPDF}，在微扰QCD中在次领先（NLO）和次领先次领先（NNLO）处执行。这种新的衍射PDF的确定是基于断裂函数的方法，QCD框架，旨在提供一个统计上合理的表示衍射DIS过程。在FONLL广义质量变味数方案（GM-VFNS）的框架内考虑了重夸克对衍射DIS的贡献，并采用“Hessian方法”确定了衍射PDF的不确定性。我们讨论了新的方面，在本分析中使用的方法，即一个优化和灵活的参数化的衍射PDF，以及一个战略的基础上，充分因式分解定理衍射硬过程。然后，我们提出了衍射PDF，并讨论了适合的质量和稳定性的变化的运动切割和拟合的数据集。我们发现，系统地包含高阶QCD修正可以改善数据的描述。我们比较了提取的组衍射PDF的断裂函数的方法的基础上，最近的其他组衍射PDF，发现在一般情况下非常好的协议。
Phenomenology of the Z-boson plus jet process at NNLO
本文详细研究了微扰QCD中Z玻色子产生与喷流通过次-次-领先阶（NNLO）的关系。给出了8 TeV和13 TeV LHC碰撞的基准截面和微分分布。我们研究了不同的部分子分布函数（PDF）的Z+喷流过程的预测的影响。在包括NNLO修正，剩余的尺度不确定性降低，使得总速率和横向动量分布可以用来区分各种PDF集。
Assessing the Impact of Fitting Methodology at aN$^3$LO with FPPDF: an Open Source Tool for Extracting Parton Distribution Functions in the Hessian Approach
Universidad de Sevilla（塞维利亚大学）；Università degli Studi di Torino and INFN, Sezione di Torino（都灵大学和意大利国家核物理研究所都灵分部）；University College London（伦敦大学学院）
Focusing on hadron scattering at large partonic momentum fractions $x$, we compare nonperturbative QCD predictions for the asymptotic behavior of DIS structure functions and parton distribution functions (PDFs) to the $x$ and $Q$ dependence of phenomenological PDFs. In the CT18 NNLO global QCD analysis, higher-order radiative contributions and functional mimicry of PDF parametrizations result in about one unit of uncertainty in the effective powers of $(1-x)$ falloff of nucleon PDFs. Similar uncertainties are present in the case of the pion PDF, an object of growing interest in phenomenology.
We present a systematic investigation of jet production at hadron colliders from a phenomenological point of view, with the dual aim of providing a validation of theoretical calculations and guidance to future determinations of parton distributions (PDFs). We account for all available inclusive jet and dijet production measurements from ATLAS and CMS at 7 and 8 TeV by including them in a global PDF determination, and comparing to theoretical predictions at NNLO QCD supplemented by electroweak (EW) corrections. We assess the compatibility of the PDFs, specifically the gluon, obtained before and…
A precise knowledge of the quark and gluon structure of the proton, encoded by the parton distribution functions (PDFs), is of paramount importance for the interpretation of high-energy processes at present and future lepton-hadron and hadron-hadron colliders. Motivated by recent progress in the PDF determinations carried out by the CT, MSHT, and NNPDF groups, we present an updated combination of global PDF fits: PDF4LHC21. It is based on the Monte Carlo combination of the CT18, MSHT20, and NNPDF3.1 sets followed by either its Hessian reduction or its replica compression. Extensive benchmark s…
We present the first-ever description the world data on the $g_1^{p,n}$ structure function at small Bjorken $x$ using evolution equations in $x$ derived from first principles QCD. This is a Monte-Carlo analysis within the JAM global framework that allows us to fit all existing polarized DIS data below $x<0.1$ as well as predict future measurements of small $x$ $g_1^{p,n}$ at the EIC. This is a necessary step in determining the quark helicity PDFs and, ultimately, the quark contribution to the proton spin.
Impact of Z-boson transverse-momentum resummation on PDF determination
Universidad de Sevilla（塞维利亚大学）；Università di Torino, and INFN, Sezione di Torino（都灵大学和意大利国家核物理研究所都灵分部）；Università di Milano-Bicocca, and INFN, Sezione di Milano-Bicocca（米兰比可卡大学和意大利国家核物理研究所米兰比可卡分部）
