Quark Helicity Distributions at Large Longitudinal Momentum Fraction
We study the quark helicity distributions at large $$x$$ in perturbative QCD, taking into account contributions from the valence Fock states of the nucleon which have nonzero orbital angular momentum. These states are necessary to have a nonzero anomalous magnetic moment. We find that the quark orbital angular momentum contributes a large logarithm to the negative helicity quark distribution in addition to its power behavior, scaling as $$(1-x)^5\log^2(1-x)$$ in the limit of $$x\to 1$$. Our analysis show that the ratio of the polarized over unpolarized down quark distributions, $$\Delta d/d$$, will still approach 1 in this limit. By comparing with the current experimental data, we find that this ratio will cross zero at $$x\approx 0.75$$.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- USDOE - Office of Energy Research (ER)
- DOE Contract Number:
- AC05-06OR23177; AC02-98CH10886
- OSTI ID:
- 903315
- Report Number(s):
- JLAB-PHY-07-644; DOE/OR/23177-0046; RBRC-671; SLAC-PUB-12503; TRN: US0703240
- Journal Information:
- Phys.Rev.Lett., Vol. 99
- Country of Publication:
- United States
- Language:
- English
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