skip to main content

Explore Research Products in the NSF-PAR

Title: Parton Distribution Functions and Lattice QCD
Recently, there have been rapid developments in lattice-QCD calculations of proton structure, especially in the parton distribution functions (PDFs). We overcame a longstanding obstacle and for the first time in lattice-QCD are able to directly calculate the Bjorken- x dependence of the quark, helicity and transversity distributions. The PDFs are obtained using the large-momentum effective field theory (LaMET) framework where the full Bjorken- x dependence of finite-momentum PDFs, called “quasi-PDFs”, can be calculated on the lattice. The quasi-PDF nucleon matrix elements are renormalized non-perturbatively in RI/MOM-scheme. Following a nonperturbative renormalization of the parton quasi-distribution in a regularization-independent momentum-subtraction scheme, we establish its matching to the $ \overline {{\rm{MS}}} $ PDF and calculate the non-singlet matching coefficient at next-to-leading order in perturbation theory. In this proceeding, I will show the progress that has been made in recent years, highlighting the latest state-of-the art PDF calculations at the physical pion mass. Future impacts on the large- x global PDF fits are also discussed.  more » « less
Award ID(s):
1653405
NSF-PAR ID:
10097103
Author(s) / Creator(s):
; ; ; ; ; ;
Date Published:
Journal Name:
EPJ Web of Conferences
Volume:
206
ISSN:
2100-014X
Page Range / eLocation ID:
01003
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ( , Probing Nucleons and Nuclei in High Energy Collisions)
    There have been rapid developments in parton distribution functions (PDFs) using lattice QCD for both precision moments and direct calculation of the Bjorken-$x$ dependence. In this talk, I show some progress along these directions and show some examples of how lattice-QCD calculations can play a significant role in improving our understanding of PDFs in the future. 
    more » « less
  2. ; ; ; ; ; ; ; ; ( , Physical review letters)
    We present a state-of-the-art calculation of the isovector quark helicity Bjorken-$x$ distribution in the proton using lattice-QCD ensembles at the physical pion mass. We compute quasi-distributions at proton momenta $P_z \in \{2.2, 2.6, 3.0\}$~GeV on the lattice, and match them systematically to the physical parton distribution using large-momentum effective theory (LaMET). We reach an unprecedented precision through high statistics in simulations, large-momentum proton matrix elements, and control of excited-state contamination. The resulting distribution is in agreement within $2\sigma$ with the latest phenomenological analysis of the spin-dependent experimental data; in particular, $\Delta \bar{u}(x)>\Delta \bar{d}(x)$. 
    more » « less
  3. ; ( , Journal of Physics G: Nuclear and Particle Physics)
    Abstract

    We present a state-of-the-art calculation of the unpolarized pion valence-quark distribution in the framework of large-momentum effective theory (LaMET) with improved handling of systematic errors as well as two-loop perturbative matching. We use lattice ensembles generated by the MILC collaboration at lattice spacinga≈ 0.09 fm, lattice volume 643× 96,Nf= 2 + 1 + 1 flavors of highly-improved staggered quarks and a physical pion mass. The LaMET matrix elements are calculated with pions boosted to momentumPz≈ 1.72 GeV with high-statistics ofO(106) measurements. We study the pion PDF in both hybrid-ratio and hybrid-regularization-independent momentum subtraction (hybrid-RI/MOM) schemes and also compare the systematic errors with and without the addition of leading-renormalon resummation (LRR) and renormalization-group resummation (RGR) in both the renormalization and lightcone matching. The final lightcone PDF results are presented in the modified minimal-subtraction scheme at renormalization scaleμ= 2.0 GeV. We show that thex-dependent PDFs are compatible between the hybrid-ratio and hybrid-RI/MOM renormalization with the same improvements. We also show that systematics are greatly reduced by the simultaneous inclusion of RGR and LRR and that these methods are necessary if improved precision is to be reached with higher-order terms in renormalization and matching.

     
    more » « less
  4. ( , Physics letters)
    null (Ed.)
    We present the first determination of the x-dependent pion gluon distribution from lattice QCD using the pseudo-PDF approach. We use lattice ensembles with 2+1+1 flavors of highly improved staggered quarks (HISQ), generated by MILC Collaboration, at two lattice spacings a≈0.12 and 0.15~fm and three pion masses Mπ≈220, 310 and 690 MeV. We use clover fermions for the valence action and momentum smearing to achieve pion boost momentum up to 2.29 GeV. We find that the dependence of the pion gluon parton distribution on lattice spacing and pion mass is mild. We compare our results from the lightest pion mass ensemble with the determination by JAM and xFitter global fits. 
    more » « less
  5. ; ; ; ; ( , XXV International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2017))
    The workshop on Parton Distributions and Lattice Calculations in the LHC era (PDFLattice2017) was hosted at Balliol College, Oxford (UK), from 22nd to 24th March 2017. The workshop brought together the lattice-QCD and the global-fit physicists who devote their efforts to determine the parton distribution functions (PDFs) of the proton. The goals were to make the two communities more familiar between each other, review developments from both sides, and set precision targets for lattice calculations so that they can contribute, together with the forthcoming experimental input, to the next generation of PDF determinations. This contribution summarises the relevant outcome of the workshop, in anticipation of a thorough white paper. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email