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Title: Chiral dynamics and partonic structure at large transverse distances

Abstract

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, (b 2) q+q¯>(b 2) 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,more » 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.« less

Authors:
 [1];  [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
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
978574
Report Number(s):
JLAB-THY-09-1012; DOE/OR/23177-0773
Journal ID: ISSN 1550-7998; TRN: US1003002
DOE Contract Number:  
AC05-06OR23177; FGO2-93ER40771
Resource Type:
Journal Article
Journal Name:
Physical Review. D, Particles, Fields, Gravitation and Cosmology
Additional Journal Information:
Journal Volume: 80; Journal Issue: 11; Journal ID: ISSN 1550-7998
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ASYMMETRY; COMPTON EFFECT; FORM FACTORS; PIONS; PRODUCTION; QUANTUM CHROMODYNAMICS; QUARKS; SEAS

Citation Formats

Strikman, M., and Weiss, C. Chiral dynamics and partonic structure at large transverse distances. United States: N. p., 2009. Web. doi:10.1103/PhysRevD.80.114029.
Strikman, M., & Weiss, C. Chiral dynamics and partonic structure at large transverse distances. United States. doi:10.1103/PhysRevD.80.114029.
Strikman, M., and Weiss, C. Wed . "Chiral dynamics and partonic structure at large transverse distances". United States. doi:10.1103/PhysRevD.80.114029. https://www.osti.gov/servlets/purl/978574.
@article{osti_978574,
title = {Chiral dynamics and partonic structure at large transverse distances},
author = {Strikman, M. and Weiss, C.},
abstractNote = {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≲Mπ/MN and transverse distances b~1/Mπ. 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, Rcore=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 Nc-scaling of parton densities in QCD, thanks to the degeneracy of N and Δ intermediate states in the large-Nc limit. Finally, we also comment on the role of pionic configurations at large longitudinal distances and the limits of their applicability at small x.},
doi = {10.1103/PhysRevD.80.114029},
journal = {Physical Review. D, Particles, Fields, Gravitation and Cosmology},
issn = {1550-7998},
number = 11,
volume = 80,
place = {United States},
year = {2009},
month = {12}
}