Hadron Structure using DWF Quarks on an Asqtad Sea
Moments of unpolarized, helicity, and transversity distributions, electromagnetic form factors, and generalized form factors of the nucleon are presented from a preliminary analysis of lattice results using pion masses down to 359 MeV[1]. We employ a hybrid approach, in which improved, staggered quarks are used for the generation of the gauge configurations, whilst domain-wall fermions, with their desirable chiral properties, are used for the valence quarks. The nucleon axial-vector charge, a benchmark quantity of QCD, is particularly robust under chiral extrapolation; the consistency of the hybrid calculation, both with other lattice calculations, and with experiment at the physical pion mass, is encouraging[2]. Lattice moments of structure functions and GPDs likewise require extrapolation to the physical quark masses; a long-standing puzzle has been the flat behavior of the flavour-non-singlet momentum fraction, <x>, of the nucleon, at a value considerably higher than the experimental value. An approach in which we apply {chi}PT, with low-energy constants g{sub A} and f{sub {pi}} given by their lattice values at each quark mass, allows a two-parameter extrapolation in m{sub {pi}}{sup lat}/f{sub {pi}}{sup lat} to yield a value for <x>, and other benchmark quantities, at the physical quark masses that are consistent with experiment. This development encourages to now exploit the predictive power of these calculations. The low-Q{sup 2} behavior of the nucleon form factors describes the distribution of charge and magnetism within a nucleon. The slope of the F{sub 1} form factor is related to the rms charge radius; the chiral extrapolation of the isovector charge radius likewise yields values consistent with experiment[3]. Generalized Parton Distributions provide new insight to hadron structure. For example, the total angular momentum carried by the quarks is related to a combination of moments J{sub q} = 1/2(A{sub 20}{sup u+d} + B{sub 20}{sup u+d})[4]. Combined with measurements of quark spins, we find the total orbital angular momentum carried by quarks is small, though that carried by individual flavours is substantial.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE - Office of Energy Research (ER)
- DOE Contract Number:
- AC05-06OR23177
- OSTI ID:
- 894734
- Report Number(s):
- JLAB-THY-06-567; DOE/ER/40150-4120; TRN: US0700236
- Resource Relation:
- Conference: Lattice QCD, Chiral Perturbation Theory and Hadron Phenomenology, 02-Oct-06, Trento, Italy
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANGULAR MOMENTUM
BENCHMARKS
ELECTROMAGNETIC FORM FACTORS
EXTRAPOLATION
FERMIONS
FORM FACTORS
HADRONS
HELICITY
ISOVECTORS
MAGNETISM
NUCLEONS
ORBITAL ANGULAR MOMENTUM
PERTURBATION THEORY
PIONS
QUANTUM CHROMODYNAMICS
QUARKS
STRUCTURE FUNCTIONS
VALENCE