Higher twists in polarized DIS and the size of the constituent quark
The spontaneous breaking of chiral symmetry implies the presence of a short-distance scale in the QCD vacuum, which phenomenologically may be associated with the ''size'' of the constituent quark, rho {approx} 0.3 fm. We discuss the role of this scale in the matrix elements of the twist-4 and 3 quark-gluon operators determining the leading power (1/Q{sup 2}-) corrections to the moments of the nucleon spin structure functions. We argue that the flavor-nonsinglet twist-4 matrix element, f{sub 2}{sup u-d}, has a sizable negative value of the order rho{sup -2}, due to the presence of sea quarks with virtualities {approx} rho{sup -2} in the proton wave function. The twist-3 matrix element, d{sub 2}, is not related to the scale rho{sup -2}. Our arguments support the results of previous calculations of the matrix elements in the instanton vacuum model. We show that this qualitative picture is in agreement with the phenomenological higher-twist correction extracted from an NLO QCD fit to the world data on g{sub 1}{sup p} and g{sub 1}{sup n}, which include recent data from the Jefferson Lab Hall A and COMPASS experiments. We comment on the implications of the short-distance scale rho for quark-hadron duality and the x-dependence of higher-twist contributions.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA
- Sponsoring Organization:
- USDOE - Office of Energy Research (ER)
- DOE Contract Number:
- AC05-84ER40150
- OSTI ID:
- 876134
- Report Number(s):
- JLAB-THY-06-468; DOE/ER/40150-3744
- Country of Publication:
- United States
- Language:
- English
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Higher twists in spin structure functions from a 'constituent quark' point of view