Parton distribution functions (PDFs) at large $x$ are poorly constrained by high-energy experimental data, but extremely important for probing physics beyond standard model at colliders. We study the calculation of PDFs at large-$x$ through large-momentum $P^z$ expansion of the lattice quasi PDFs. Similar to deep-inelastic scattering, there are two distinct perturbative scales in the threshold limit where the matching coefficient can be factorized into a space-like jet function at scale $P^z|1-y|$ and a pair of heavy-light Sudakov form factors at scale $P^z$. The matching formula allows us to derive a full renormalization group resummation of large threshold logarithms, and the result is consistent with the known calculation to the next-to-next to leading order (NNLO). This paves the way for direct large-$x$ PDFs calculations in lattice QCD. As by-products, we find that the space-like jet function is related to a time-like version calculated previously through analytic continuation, and the heavy-light Sudakov form factor, calculated here to NNLO, is a universal object appearing as well in the large momentum expansion of quasi transverse-momentum-dependent PDFs and quasi wave-function amplitudes.
We perform the first global QCD analysis of pion valence, sea quark, and gluon distributions within a Bayesian Monte Carlo framework with threshold resummation on Drell-Yan cross sections at next-to-leading log accuracy. Exploring various treatments of resummation, we find that the large-$x$ asymptotics of the valence quark distribution $\sim (1-x)^{β_v}$ can differ significantly, with $β_v$ ranging from $\approx 1$ to $> 2.5$ at the input scale. Regardless of the specific implementation, however, the resummation induced redistribution of the momentum between valence quarks and gluons boosts t…
We discuss perturbative solutions of renormalization group equations, and propose the use of resummation scale techniques in assessing theoretical uncertainties on the extraction of parton distribution functions from data.
I report on precision comparisons of theoretical predictions for Drell-Yan (DY) transverse momentum spectra from two approaches: the analytical resummation approach based on Collins-Soper-Sterman (CSS) formalism and the parton branching (PB) approach to the evolution of transverse momentum dependent (TMD) parton distributions.
Collider observables involving heavy particles are subject to large logarithmic terms near threshold, which must be summed to all orders in perturbation theory to obtain sensible results. Relatively recently, this resummation has been extended to next-to-leading power in the threshold variable, using a variety of approaches. In this paper, we consider partonic channels that turn on only at next-to-leading power, and show that it is possible to resum leading logarithms using well-established diagrammatic techniques in Quantum Chromodynamics. We first consider deep inelastic scattering, where we…
Infrared Singularities and Soft Gluon Resummation with Massive Partons
QCD散射振幅的红外发散可以从反常维数矩阵中导出，这也是软胶子发射产生的大振幅的重新计算的一个重要组成部分。本文报道了最近在双圈水平上对有质量部分子和无质量部分子的反常维数矩阵的解析计算，它描述了任意数量的有质量部分子和无质量部分子的散射振幅的双圈红外奇异性，并使软胶子能以次-次-首对数级重算.作为应用，我们计算了q qbar -> t tbar和gg -> t tbar散射振幅中的红外极点。
The new precision era of jet quenching observables at both RHIC and the LHC calls for an improved and more precise description of in-medium gluon emissions. The development of new theoretical tools and analytical calculations to tackle this challenge has been hampered by the inability to include the effects of multiple scatterings with the medium using a realistic model for the parton-medium interactions. In this paper, we show how the analytical expressions for the full in-medium spectrum, including the resummation of all multiple scatterings, can be written in a form where the numerical eval…
Threshold resummation of rapidity distributions at fixed partonic rapidity
Technische Universität München（慕尼黑工业大学）；Johannes Gutenberg-Universität Mainz（美因茨约翰内斯·古腾堡大学）；Università di Milano and INFN, Sezione di Milano（米兰大学与意大利国家核物理研究所米兰分部）；Università di Genova and INFN, Sezione di Genova（热那亚大学与意大利国家核物理研究所热那亚分部）
The off-diagonal parton-scattering channels $g+γ^*$ and $q+ϕ^*$ in deep-inelastic scattering are power-suppressed near threshold $x\to 1$. We address the next-to-leading power (NLP) resummation of large double logarithms of $1-x$ to all orders in the strong coupling, which are present even in the off-diagonal DGLAP splitting kernels. The appearance of divergent convolutions prevents the application of factorization methods known from leading power resummation. Employing $d$-dimensional consistency relations from requiring $1/ε$ pole cancellations in dimensional regularization between momentum …
We discuss recent progress concerning the resummation of large logarithms at next-to-leading power (NLP) in scattering processes near threshold. We begin by briefly reviewing the diagrammatic and SCET approach, which are used to derive factorization theorems for physical observables in this kinematic limit. Then, we focus on the quark-gluon channel in deep inelastic scattering and Drell-Yan. We show that the use of consistency conditions for the cancellation of leading poles in the hadronic cross section can be used to achieve the resummation of large leading logarithms (LLs) at NLP, both with…
Many present lattice QCD approaches to calculate the parton distribution functions (PDFs) rely on a factorization formula or effective theory expansion of certain Euclidean matrix elements in boosted hadron states. In the quasi- and pseudo-PDF methods, the matching coefficient in the factorization or expansion formula includes large logarithms near the threshold, which arise from the subtle interplay of collinear and soft divergences of an underlying 3D momentum distribution. We use the standard prescription to resum such logarithms in the Mellin-moment space at next-to-leading logarithmic acc…
Precision QED \otimes QCD Resummation Theory for LHC Physics: IR-Improved Scheme for Parton Distributions, Kernels, Reduced Cross Sections with Shower/ME Matching
