Chiral dynamics and partonic structure at large transverse distances

Journal Article · Tue Dec 01 04:00:00 EST 2009 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.80.114029· OSTI ID:21313484

Strikman, M ^[1]; Weiss, C ^[2]

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1. Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802 (United States)
2. Theory Center, Jefferson Lab, Newport News, Virginia 23606 (United States)

We study large-distance contributions to the nucleon's parton densities in the transverse coordinate (impact parameter) representation based on generalized parton distributions (GPDs). Chiral dynamics generates a distinct component of the partonic structure, located at momentum fractions x < or approx. M{sub {pi}}/M{sub N} and transverse distances b{approx}1/M{sub {pi}}. We calculate this component using phenomenological pion exchange with a physical lower limit in b (the transverse 'core' radius estimated from the nucleon's axial form factor, R{sub core}=0.55 fm) and demonstrate its universal character. This formulation preserves the basic picture of the 'pion cloud' model of the nucleon's sea quark distributions, while restricting its application to the region actually governed by chiral dynamics. It is found that (a) the large-distance component accounts for only {approx}1/3 of the measured antiquark flavor asymmetry d-u at x{approx}0.1; (b) the strange sea quarks s and s are significantly more localized than the light antiquark sea; (c) the nucleon's singlet quark size for x<0.1 is larger than its gluonic size, <b{sup 2}>{sub q+q}><b{sup 2}>{sub g}, as suggested by the t-slopes of deeply-virtual Compton scattering and exclusive J/{psi} production measured at HERA and FNAL. We show that our approach reproduces the general N{sub c}-scaling of parton densities in QCD, thanks to the degeneracy of N and {delta} intermediate states in the large-N{sub c} limit. We also comment on the role of pionic configurations at large longitudinal distances and the limits of their applicability at small x.

• OSTI ID: 21313484
• Journal Information: Physical Review. D, Particles Fields, Journal Name: Physical Review. D, Particles Fields Journal Issue: 11 Vol. 80; ISSN PRVDAQ; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANTIQUARKS
ASYMMETRY
CHIRALITY
COMPTON EFFECT
COMPUTERIZED SIMULATION
CONFIGURATION
DENSITY
DISTRIBUTION
FLAVOR MODEL
FORM FACTORS
HERA STORAGE RING
IMPACT PARAMETER
INTERMEDIATE STATE
J PSI-3097 MESONS
NUCLEONS
PARTICLE PRODUCTION
PIONS
QUANTUM CHROMODYNAMICS
QUARK MATTER
SCATTERING