1 / 28

Hadron Structure and Nucleon Properties from Light Quark Masses and Lattice QCD

This study explores the structure of hadrons, focusing on nucleon properties, form factors, and the impact of light quark masses. Utilizing Domain-Wall Fermions (DWF) and Asqtad light sea quarks, the research examines crucial aspects such as momentum fractions, spin distributions, and generalized parton distributions (GPDs). The findings illustrate the interplay between perturbative and non-perturbative QCD aspects, particularly in pion form factors, providing valuable insights into nucleon and meson dynamics. Preliminary results hint at the critical influence of the pion cloud in these computations.

ranit
Télécharger la présentation

Hadron Structure and Nucleon Properties from Light Quark Masses and Lattice QCD

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Hadron Structure at Light Quark Masses DWF Valence on a Asqtad light sea Nucleon Properties: Form Factors gA Momentum and Spin Fraction GPDs Pion Form Factor David Richards (Jefferson Laboratory) for LHPC

  2. LHP Collaboration • Dru RennerUniversity of Arizona • Richard Brower, James Osborn Boston University • Rebecca Irwin, Michael Ramsey-Musolf CalTech • Robert Edwards, David Richards JLab • Bojan Bistrovic, Jonathan Bratt, Patrick Dreher, Oliver Jahn, John Negele, Kostas Orginos, Andrew Pochinsky, Dmitry SigaevMIT • Matthias Burkardt, Michael Engelhardt New Mexico State University • George Fleming Yale • Constantia Alexandrou, Antonios Tsapalis Cyprus, Wolfram Schroers DESY, Philippe de Forcrand EHT-Zurich,Philipp Hägler Vrije Universiteit Many transparencies

  3. Light quark masses Onward to light pion masses…. • Achievable precision limited by lightest pion mass Flavor-non-singlet momentum fraction in nucleon. Detmold et al, PRL87, 172001 (2001) Expt value • Exact chiral symmetry at Finite Spacing a • Domain-wall fermions (DWF) in five dimensions

  4. DWF Computations • MILC Asqtad lattices – staggered sea quarks • Conventional DWF valence quarks computed on HYP-smeared lattices: use non-perturbative HYP parameters. • Lattices bisected in temporal direction – DWF propagators computed using Dirichlet boundary conditions on half lattice • M5 = 1.7 – Ls = 16 • Parameter matching – tune DWF pion to match Asqtad Goldstone pion mass m • a = 0.13 fm, two volumes at lightest pion mass PRD64, 034504

  5. DWF parameters m L = 4.5 m L = 6.3 Alternate configs on first and second halves of lattice

  6. Pion mass matching.. DWF Pion matched toGoldstone Pion

  7. Setting L5 Residual mass • Finite L5 induces extra term in divergence of axial current 4-D PCAC from 5-D CVC Domain walls Ja5q 0 L5 - 1

  8. Residual mass….

  9. Residual Mass….. Pion Nucleon

  10. Meson masses….. Pion Rho

  11. Baryon masses…. Nucleon Delta

  12. DIS and GPD’s for Nucleons • Measures light-cone correlation functions • DIS gives diagonal matrix element • DVCS gives off-diagonal matrix element

  13. J N N Moments of Structure Functions and GPD’s q p • Generates tower of twist-two operators • Expand O(x) around light-cone • Diagonal matrix element • Off-diagonal matrix element

  14. Moments….. • GPDs and GFFs are related through Mellin Transformation: • Generalized Form Factors familiar quantities

  15. Renormalization of Operators • One-loop renormalization of operators in boosted perturbation theory: B. Bistrovic, PhD Thesis, MIT 2005 HYP Constants close to unity

  16. Nucleon EM Form Factors - I • At large Q2, scaling predicted by Brodsky and Lepage: • F1» Q-4 and F2» Q-6 • Perturbative corrections Phys. Rev. Lett. 88, 092301 (2002) Brodsky; Belitsky, Ji, Yuan

  17. Nucleon EM Form Factors - II Preliminary • I = 1 form factors to remove disconnected contributions F1I = 1 = F1p – F1n • Neutron form factors poorly known for Q2 > 1 GeV2 • Form factors normalized F2(Q2) !as Q2! 0

  18. Nucleon EM Form Factors - III • F2I=1/F1I=1!p - n as Q2! 0. • Use PDG ’s

  19. Nucleon Axial Charge - I • Nucleon axial charge – benchmark computation • Chiral behavior expected to be mild LHPC Preliminary Two volumes

  20. Axial Charge - II • Hemmert, hep-lat/0303002 • Two free parameters: gNNA, and gA. • Remaining parameters from phenomenology f, gNA, m - mN, B9 - gA B20.

  21. Momentum Fraction <x> - Preliminary Unsmeared links Z = 1 Smeared links

  22. Polarized - Preliminary Smeared links Z = 1 Orginos, Blum, Ohta – hep-lat/0505024

  23. Generalized form factors… Decrease slope : decreasing transverse size as x ! 1 Burkardt

  24. Transverse distribution A30: 2.6 +- .8 GeV A20: 1.85 +- 0.06

  25. Pion Form Factor –I • Laboratory for observing interplay between perturbative and non-perturbative aspects of QCD • Asymptotic normalization determined • Small Q2, vector-meson dominance provides faithful description • Free of disconnected contributions – straightforward lattice calculation Scale?

  26. Pion Form Factor –II • Current and Projected Experimental Situation

  27. Pion Form Factor –III LHPC, Bonnet et al hep-lat/0411028 • Pion Form factor over Q2 commensurate with experiment • Pion GPDs and transition form factors

  28. Conclusions and Perspective • Use of hybrid Asqtad/DWF calculation providing entry into pion-cloud regime for range of physical quantities – spectrum, nucleon and meson form factors and transition form factors, moments of PDF’s and GPD’s… • Preliminary results – more complete analysis for Dublin • Computations being extended both to smaller values of lattice spacing (a=0.9, 0.6 fm), and to lighter m = 250 MeV – reveal effects of pion cloud. • Disconnected diagrams, transition form factors…

More Related