Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session QC: Parton Distributions from Lattice QCD |
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Chair: Kyle Shiells, Center of Nuclear Femtography Room: Studio 2 |
Thursday, October 14, 2021 11:30AM - 11:42AM |
QC.00001: Recent Parton-Distribution Results from Lattice QCD at Physical Pion Mass Huey-Wen Lin There have been rapid developments in the direct calculation of the Bjorken-x dependence of parton distribution functions (PDFs) using lattice QCD. Among various new methods, large-momentum effective theory (LaMET), which calculates boosted hadron matrix elements at multiple spatial displacements on the lattice, shows promising PDFs. In this talk, I will report a few recent results on pion PDFs and nucleon generalized parton distributions (GPDs) calculated directly at the physical pion mass. |
Thursday, October 14, 2021 11:42AM - 11:54AM |
QC.00002: Towards High-Precision Nucleon Parton Distributions via Distillation in Lattice QCD Colin P Egerer, Robert Edwards, Christos Kallidonis, Kostas Orginos, Anatoly V Radyushkin, David G Richards, Eloy Romero, Savvas Zafeiropoulos Parton distribution functions (PDFs) are indispensable measures of hadronic structure, and complement the hadron tomography efforts of the nuclear physics community. Despite characterizing the non-perturbative collinear dynamics of a hadron involved in a (semi-)inclusive process, the light-like intervals of PDFs cannot be realized using the first-principles tool of Lattice QCD (LQCD). The pseudo-distribution formalism is one of several contemporary LQCD methodologies capable of exposing the collinear structure of hadrons from a class of space-like operators. Leveraging the distillation spatial smearing program, we extract the unpolarized isovector valence quark PDF of the nucleon via a direct 1-loop matching of the Ioffe-time pseudo-distribution (pseudo-ITD) and model PDFs. The statistical quality of the isolated pseudo-ITD is seen to be considerably more precise than the literature, opening the possibility of rigorously quantifying systematic effects inherent to the pseudo-distribution formalism. We implement a scheme to simultaneously extract the desired PDFs, while capturing and removing several contaminating effects - the most significant being a short-distance discretization effect. Broadly, this scheme bolsters the prospect of a reliable leading-twist PDF extraction. |
Thursday, October 14, 2021 11:54AM - 12:06PM |
QC.00003: Gluon Parton Distribution on the Lattice using Pseudo-PDF technique Tanjib Khan, Raza S Sufian, Joseph M Karpie, Christopher Monahan, Balint Joo, Wayne Morris, Kostas Orginos, Anatoly V Radyushkin, David G Richards, Eloy Romero, Savvas Zafeiropoulos We present a calculation of the unpolarized gluon parton distribution function (PDF) in the nucleon using the Pseudo-PDF framework. The nucleon interpolating fields are constructed using distillation and we apply the sGEVP method to calculate the gluonic matrix elements. We modify the gauge fields using gradient flow, and form a double ratio of matrix elements to yield the flowed reduced matrix elements. We extrapolate the results to the zero flow-time limit to calculate the pseudo Ioffe-time distribution. We extract the unpolarized gluon PDF directly from pseudo-ITD by implementing Jacobi ploynomial parametrization. We describe the prospect of polarized gluon PDF calculation by showing some preliminary results. |
Thursday, October 14, 2021 12:06PM - 12:18PM |
QC.00004: Pseudo-distributions at short distances in the forward limit Wayne Morris, Ian Balitsky, Anatoly V Radyushkin We present the results that are necessary in the ongoing lattice calculations of the unpolarized and polarized gluon parton distribution functions (PDFs) within the pseudo-PDF approach. We give a classification of possible two-gluon correlator functions and identify those that contain the invariant amplitude determining the gluon PDF in the light-cone z2 → 0 limit. One-loop calculations have been performed in the coordinate representation and in an explicitly gauge-invariant form. We made an effort to separate ultraviolet (UV) and infrared (IR) sources of the log(-z2)-dependence at short distances z2. The UV terms cancel in the reduced Ioffe-time distribution (ITD), and we obtain the matching relation between the reduced ITD and the light-cone ITD. Using a kernel form, we get a direct connection between lattice data for the reduced ITD and the normalized gluon PDF. |
Thursday, October 14, 2021 12:18PM - 12:30PM |
QC.00005: Review on Linear Divergence Yushan Su Large-momentum effective theory provides a way to extract the parton physics from lattice data based on first-principle calculation. In applying large-momentum effective theory, renormalization of the Euclidean correlators in lattice regularization is a challenge due to linear divergences in the self-energy of Wilson lines. We will give a review on different renormalization methods to deal with linear divergences, including RI/MOM, ratio scheme and vacuum matrix elements. In these renormalization methods, people divide the bare hadron matrix element by another matrix element. Then we will talk about the self-renormalization method proposed recently, including a detailed numerical test on the linear divergence factors in the previous methods. Our test shows that the linear divergence can be eliminated in the ratio scheme. Moreover, we find a large non-perturbative effect in the RI/MOM and ratio scheme, suggesting favor of the hybrid renormalization procedure proposed recently. Finally, we will talk about the hybrid renormalization method. |
Thursday, October 14, 2021 12:30PM - 12:42PM |
QC.00006: The Collins-Soper Kernel from Lattice QCD with Dynamical Fermions Yong Zhao, Phiala E Shanahan, Michael L Wagman In this talk, I present a lattice quantum chromodynamics calculation of the nonperturbative Collins-Soper kernel, which describes the energy evolution of quark transverse-momentum-dependent parton distribution functions. The kernel is extracted at transverse momentum scales in the range 400~MeV~$< q_T < 1.7$~GeV in a calculation with dynamical fermions and a larger-than-physical pion mass, with systematic treatment of operator mixings, Fourier transform, perturbative matching and power corrections. |
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