Chiral dynamics and partonic structure at large transverse distances

Journal Article · Wed Dec 30 04:00:00 EST 2009 · Physical Review. D, Particles, Fields, Gravitation and Cosmology

DOI:https://doi.org/10.1103/PhysRevD.80.114029· OSTI ID:978574

Strikman, M. ^[1]; Weiss, C. ^[2]

---

1. Pennsylvania State Univ., University Park, PA (United States). Dept. of Physics
2. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States). Theory Center

In this paper, 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≲M_π/M_N and transverse distances b~1/M_π. 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_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 ~1/3 of the measured antiquark flavor asymmetry d¯-u¯ at x~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, (b²)_q+q¯>(b²)_g, as suggested by the t-slopes of deeply-virtual Compton scattering and exclusive J/ψ production measured at HERA and FNAL. We show that our approach reproduces the general N_c-scaling of parton densities in QCD, thanks to the degeneracy of N and Δ intermediate states in the large-N_c limit. Finally, we also comment on the role of pionic configurations at large longitudinal distances and the limits of their applicability at small x.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 978574
• Report Number(s): JLAB-THY--09-1012; DOE/OR/23177--0773
• Journal Information: Physical Review. D, Particles, Fields, Gravitation and Cosmology, Journal Name: Physical Review. D, Particles, Fields, Gravitation and Cosmology Journal Issue: 11 Vol. 80; ISSN 1550-7998
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ASYMMETRY
COMPTON EFFECT
FORM FACTORS
PIONS
PRODUCTION
QUANTUM CHROMODYNAMICS
QUARKS
SEAS