We present an update of the ABM12 PDF analysis including improved constraints due to the final version of the inclusive DIS HERA data, the Tevatron and LHC data on the W- and Z-production and those on heavy-quark production in the electron- and neutrino-induced DIS at HERA and the fixed-target experiments NOMAD and CHORUS. We also check the impact of the Tevatron and LHC top-quark production data on the PDFs and the strong coupling constant. We obtain $α_s(M_Z)=0.1145(9)$ and $0.1147(8)$ with and without the top-quark data included, respectively.
We analyze the impact of the recent HERA run I+II combination of inclusive deep inelastic scattering cross-section data on the CT14 global analysis of PDFs. New PDFs at NLO and NNLO, called CT14$_{\textrm{HERA2}}$, are obtained by a refit of the CT14 data ensembles, in which the HERA run I combined measurements are replaced by the new HERA run I+II combination. The CT14 functional parametrization of PDFs is flexible enough to allow good descriptions of different flavor combinations, so we use the same parametrization for CT14$_{\textrm{HERA2}}$ but with an additional shape parameter for descri…
We investigate the effect of including the HERA run I + II combined cross section data on the MMHT2014 PDFs. We present the fit quality within the context of the global fit and when only the HERA data are included. We examine the changes in both the central values and uncertainties in the PDFs. We find that the prediction for the data is good, and only relatively small improvements in $χ^2$ and changes in the PDFs are obtained with a refit at both NLO and NNLO. PDF uncertainties are slightly reduced. There is a small dependence of the fit quality on the value of $Q^2_{\min}$. This can be impro…
We introduce a new parametrization for the parton distribution functions (PDFs) designed to be flexible in the small-x region. We implement it in the xFitter open-source PDF fitting tool, and compare it to the default xFitter parametrization, widely used for many PDF studies, and notably for the HERAPDF determination. We find that we can describe the combined inclusive HERA I+II data using NNLO theory with a significantly higher quality than HERAPDF2.0: the $χ^2$ is reduced by more than 60 units, having used only four more parameters. Our result highlights a significant parametrization bias in…
A new parametrization for the parton distribution functions with a higher flexibility in the small-$x$ region is presented. It has been implemented in the xFitter open-source PDF fitting tool, and compared to the default xFitter parametrization, used for the determination of the HERAPDF set. It has been found that the combined inclusive HERA I+II data can be described using NNLO theory with a significantly higher quality than HERAPDF2.0: the $χ^2$ is reduced by more than 60 units, having used only four more parameters. Our result highlights a significant parametrization bias in the default xFi…
The high-precision HERA data can be used as an input to a QCD analysis within the DGLAP formalism to obtain the detailed description of the proton structure in terms of the parton distribution functions (PDFs). However, when searching for Beyond Standard Model (BSM) contributions in the data one should take into account the possibility that the PDF set may already have been biased by partially or totally absorbing previously unrecognised new physics contributions. The ZEUS Collaboration has proposed a new approach to the BSM analysis of the inclusive $ep$ data based on the simultaneous QCD fit…
Fits to the final combined HERA deep-inelastic scattering cross-section data within the conventional DGLAP framework of QCD have shown some tension at low $x$ and low $Q^2$. A resolution of this tension incorporating $\ln(1/x)$-resummation terms into the HERAPDF fits is investigated using the xFitter program. The kinematic region where this resummation is important is delineated. Such high-energy resummation not only gives a better description of the data, particularly of the longitudinal structure function $F_L$, it also results in a gluon PDF which is steeply rising at low $x$ for low scales…
We use the dipole model to analyze the inclusive DIS cross section data, obtained from the HERA I+II measurements \cite{Abramowicz:2015mha}. We show that these combined data are very well described within the dipole model framework, which is complemented with a valence quark structure functions. Our motivation is to investigate the gluon density with the BGK dipole model \cite{BGK} as an alternative to the PDF approach. BGK dipole model uses for evolution the DGLAP mechanism in the $kt$ factorization scheme (in contrast to the collinear factorization for PDFs). We confirm our results from the …
The xFitter project (former HERAFitter project) is an open-source package that provides a framework for the determination of the parton distribution functions (PDFs) of the proton for many different kinds of analyses in Quantum Chromodynamics (QCD). xFitter version 2.0.0 has recently been released, and offers an expanded set of tools and options. It incorporates experimental data from a wide range of experiments including fixed-target, Tevatron, HERA, and LHC. xFitter can analyze this data up to next-to-next-to-leading-order (NNLO) in perturbation theory with a variety of theoretical calculati…
部分子分布函数（PDF）是强子对撞机上几乎所有理论预测的不可协商的输入。在这个演讲中，我介绍了PDF测定的全球分析和讨论选定的主题有关最近的相关数据从HERA和Tevatron，然后给出一些LHC的前景。H1和ZEUS截面的组合减少了不确定性，并将成为未来全球PDF分析的重要输入。HERA中重夸克对结构函数贡献的理论描述对LHC的预测有着重要的影响。来自Tevatron Run II的新的W和Z数据提供了重要的PDF约束，但是目前描述来自W -> l nu衰变的轻子电荷不对称性的最新数据存在问题。Tevatron运行II喷气生产数据更喜欢一个较小的高x胶子比以前的运行I数据，这对预测希格斯截面在Tevatron的影响。现在可以一致地计算强子截面的组合“PDF+alpha_S”不确定性，对于LHC的W和Z总截面，其约为2-3%，反映了它们作为测量机器光度的“标准烛光”的潜力。部分子光度函数是研究强子截面性质的有用量。LHC的精确测量将为PDF提供进一步的限制，因为数据在早期运行期间积累。
The effect of full $7$ sets of LHC ATLAS jet cross sections data at $ \sqrt{s} = 7$ TeV on the proton parton distribution functions (PDFs) up to next-to-next-to-next-to-leading order (NNNLO or N3LO) corrections is investigated for the first time. Phenomenologically, the proton central PDFs in this perturbative Quantum Chromo Dynamics (pQCD) analysis are defined based on the full seven data sets from HERA I and II combined. It is shown that, the LHC ATLAS jet cross sections data at $ \sqrt{s} = 7$ TeV on the HERA I and II combined data reduces the error band of proton PDFs. Particularly, the un…
We present the new MSHT20 set of parton distribution functions (PDFs) of the proton, determined from global analyses of the available hard scattering data. The PDFs are made available at NNLO, NLO, and LO, and supersede the MMHT14 sets. They are obtained using the same basic framework, but the parameterisation is now adapted and extended, and there are 32 pairs of eigenvector PDFs. We also include a large number of new data sets: from the final HERA combined data on total and heavy flavour structure functions, to final Tevatron data, and in particular a significant number of new LHC 7 and 8 Te…
One of the most popular definition for the charm-quark mass is the charm-quark pole mass $m_c^{\rm pole}$. In this contribution, we extract the charm-quark pole mass through perturbative Quantum Chromo Dynamics (pQCD) analysis up to the next-to-next-to-leading order (NNLO) corrections from HERA Combined and LHCb charm production recent data sets. Then, we investigate for the first time the charm-quark pole mass $m_c^{\rm pole}$ pure impact, as an extra pQCD parameter on the proton Parton Distribution Functions (PDFs) at the NNLO corrections.
We discuss the impact of heavy-flavor production measurements in semi-inclusive deep inelastic scattering at HERA on the CTEQ-TEA PDFs. In particular, we study the impact of the latest charm and bottom production measurements from the H1 and ZEUS collaborations on the gluon, and the interplay of these measurements with the data ensemble of the recent CT18 global QCD analysis.
测量轻子和核子的深度非弹性散射（DIS），$e+p\to e+X$，可以提取部分子分布函数（PDF），它描述了组成快速运动核子的夸克、反夸克和胶子所携带的纵向动量。虽然PDF为涉及强子的微扰量子色动力学（QCD）计算提供了重要的输入，但它们并没有提供核子部分子结构的完整图像。特别是，PDF既不包含关于部分子之间的相关性的信息，也不包含关于它们的横向运动的信息。近年来，核子保持完整的硬排他过程已经成为补充这一基本一维图像的主要候选者。最简单的排斥过程是深虚康普顿散射（DVCS）或排斥产生实光子$e + p \to e + γ+ p$。这个过程是特别感兴趣的，因为它既有一个明确的实验签名，是可计算的微扰QCD。DVCS反应可以被看作是虚光子通过无色交换从质子上弹性散射，产生最终状态的实光子。在Bjorken标度体系中，QCD计算假设交换涉及两个部分子，具有不同的纵向和横向动量，在无色的配置。这些不相等的动量或偏斜是入射虚光子和出射实光子之间质量差的结果。这种偏态效应可以在广义部分子分布（GPD）的背景下解释。在这一过程中，我们研究了HERA的典型测量和CERN的COMPASS的前景，这可以为核子的夸克/胶子成像带来新的见解。
In this contribution, I present a new QCD fit to final combined HERA deep-inelastic scattering cross-section data incorporating $\ln(1/x)$-resummation terms. This fit has been performed within the xFitter framework. The main effect of including such resummed terms results not only in a better description of the low-$x$ and low-$Q^{2}$ data, but also in a steeply rising gluon PDF at low x for low scales. Furthermore, the kinematic region where this resummation is important is delineated. This contribution is based on the results presented in arXiv:1802.00064.
The extension of interpolation-grid frameworks for perturbative QCD calculations at next-to-next-to-leading order (NNLO) is presented for deep inelastic scattering (DIS) processes. A fast and flexible evaluation of higher-order predictions for any a posteriori choice of parton distribution functions (PDFs) or value of the strong coupling constant is essential in iterative fitting procedures to extract PDFs and Standard Model parameters as well as for a detailed study of the scale dependence. The APPLfast project, described here, provides a generic interface between the parton-level Monte Carlo…
We compare the cross section for exclusive $J/ψ$ photoproduction calculated at NLO in the collinear factorization approach with HERA and LHCb data. Using the optimum scale formalism together with the subtraction of the low $k_t<Q_0$ contribution from the NLO coefficient function to avoid double counting we show that the existing global parton distribution functions (PDFs) are consistent with the data within their uncertainties. However, at low $x$ the uncertainties of the present global PDFs are large. On the other hand, the accuracy of the LHCb data are rather good. Therefore, these data prov…
We investigate the variation in the MMHT2014 PDFs when we allow the heavy quark masses $m_c$ and $m_b$ to vary away from their default values. We make PDF sets available in steps of $Δm_c =0.05~{\rm GeV}$ and $Δm_b =0.25~{\rm GeV}$, and present the variation in the PDFs and in the predictions. We examine the comparison to the HERA data on charm and beauty structure functions and note that in each case the heavy quark data, and the inclusive data, have a slight preference for lower masses than our default values. We provide PDF sets with 3 and 4 active quark flavours, as well as the standard va…
The HERAPDF2.0 ensemble of parton distribution functions (PDFs) was introduced in 2015. The final stage is presented, a next-to-next-to-leading-order (NNLO) analysis of the HERA data on inclusive deep inelastic $ep$ scattering together with jet data as published by the H1 and ZEUS collaborations. A perturbative QCD fit, simultaneously of $α_s(M_Z^2)$ and and the PDFs, was performed with the result $α_s(M_Z^2) = 0.1156 \pm 0.0011~{\rm (exp)}~ ^{+0.0001}_{-0.0002}~ {\rm (model}$ ${\rm +~parameterisation)}~ \pm 0.0029~{\rm (scale)}$. The PDF sets of HERAPDF2.0Jets NNLO were determined with separa…
Resummation-scale uncertainties in PDF determinations
School of Physics, Institute for Research in Fundamental Sciences (IPM)（基础科学研究所）；Department of Physics, Malayer University（马拉耶尔大学物理系）；IRFU, CEA, Université Paris-Saclay（巴黎萨克雷大学CEA IRFU）；Dipartimento di Fisica, Universitá di Cagliari（卡利亚里大学物理系）；INFN, Sezione di Cagliari（意大利国家核物理研究院卡利亚里分部）；Universitá degli Studi Link（林克大学）；INFN Sezione di Roma Tor Vergata（意大利国家核物理研究院罗马托维加塔分部）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器）；Physik-Institut, Universität Zürich（苏黎世大学物理学院）；Theoretical Physics Department, University of Oxford（牛津大学理论物理系）；SMU Physics（南卫理公会大学物理系）；University of Sharjah（沙迦大学）；II. Institut für Theoretische Physik, Universität Hamburg（汉堡大学第二理论物理研究所）
The production of $W$/$Z$-bosons in association with jets is an important test of perturbative QCD predictions and also yields information about the parton distribution functions of the proton. We present fits to determine PDFs using inclusive $W$/$Z$-boson and $W$/$Z$+jets measurements from the ATLAS experiment at the LHC. The ATLAS measurements are used in combination with deep-inelastic scattering data from HERA. An improved determination of the sea-quark densities at high Bjorken-$x$ is seen, while confirming a strange-quark density similar in size to the up- and down-sea-quark densities i…
In this work we have solved the nonlinear GLR-MQ evolution equation upto next-to-leading order (NLO) by considering NLO terms of the gluon-gluon splitting functions and running coupling constant $α_s(Q^2)$. Here, we have incorporated a Regge-like behaviour of gluon distribution in order to obtain a solution of the GLR-MQ equation in the range of $5 GeV^2 \leq Q^2 \leq 25 GeV^2$. We have studied the $Q^2$ evolution of the gluon distribution function $G(x,Q^2)$ and its nonlinear effects at small-x. It can be observed from our analysis that the nonlinearities increase with decrease in the correla…
We present an updated version of the ABMP16 nucleon PDFs, which is tuned by using recent precise data on $W$- and $Z/γ^*$-production at the LHC and the final HERA data on DIS $c$- and $b$-quark production and by imposing a stringent $Q^2$-cut on the inclusive DIS data in order to avoid the impact of higher twist terms at small $x$ at HERA. The new $W$- and $Z$-boson production data, in particular the updated version of the ATLAS data at the c.m.s. energy 7 TeV, are well accommodated into the present fit. The strange sea distribution obtained is consistent with the average of the up and down qu…
