Quark–hadron duality in electron scattering

Abstract

Abstract. Quark-hadron duality addresses some of the most fundamental issues in strong interaction physics, in particular the nature of the transition from the perturbative to non-perturbative regions of QCD. I summarize recent developments in quarkhadron duality in lepton-hadron scattering, and outline how duality can be studied at future high-luminosity facilities such as Jefferson Lab at 12 GeV or an electron-hadron collider such as EPIC. I INTRODUCTIONUnderstanding the structure and interaction of hadrons in terms of the quark and gluon degrees of freedom of QCD is the greatest unsolved problem of the Standard Model of nuclear and particle physics. If one accepts QCD as the correct theory of the strong interactions, then the transition from quark-gluon to hadron degrees of freedom should in principle amount to a change of basis, with all physical quantities independent of which basis is used. However, although the duality between quark and hadron descriptions is formally exact, in practice the necessity of truncating any Fock state expansion means that the extent to which duality holds reflects the validity of the truncations under different kinematical conditions and in different physical processes. Quark-hadron duality is therefore an expression of the relationship between confinement and asymptotic freedom, and is intimately related to the nature of the transition from non-perturbative to perturbative QCD.In nature, the phenomenon of duality is in fact quite general and can be studied in a variety of processes, such as e + e − → hadrons, or heavy quark decays [1]. One of the more intriguing examples, initially observed some 30 years ago, is in inclusive inelastic electron-nucleon scattering.

Scaling and resonances in elementaryK+Λphotoproduction

“…Possible small variation around the scaled value in Fig. 3 suggests the validity of local duality [15,16]; however, the study of the latter is beyond the scope of this paper.…”

Nucleon and pion distribution functions in the valence region

“…Whilst it has been observed that the standard application of DGLAP evolution to deep inelastic structure functions can appear to be inconsistent with Bloom-Gilman duality at fixed W , this apparent conflict is resolved if one takes into account the fact that the struck quark is far-off shell in the x → 1 domain (Brodsky, 2005;Lepage and Brodsky, 1980). Underlying Bloom-Gilman duality is the assumption of quark-hadron duality; namely, a belief that one obtains equivalent descriptions of physical phenomena irrespective of whether one uses partonic or hadronic degrees-of-freedom (Melnitchouk et al, 2005;Shifman, 2000).…”

Precise determination of the deuteron spin structure at low to moderateQ2with CLAS and extraction of the neutron contribution

“…Moments of structure functions from proton and neutron access different matrix elements of local operators within the Operator Product Expansion approach [5][6][7]. Finally, a better understanding of the phenomenon of quark-hadron duality [8,9] requires detailed studies of polarized as well as unpolarized structure functions of both nucleons in the resonance and DIS regions. While suitable free neutron targets do not exist, one can extract spin structure functions for a bound neutron using polarized nuclei like 2 H and 3 He, using some prescription to account for Fermi-motion and the effective polarization of nucleons in nuclei.…”