Quarks and gluons in hadrons and nuclei Page: 21 of 31
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and so a difference between gA(0) and gA/gV can, after radiative corrections,
reveal nonzero es. (Our es 1.25n of Ref. 32.)
A practical problem is that vp vp is detected by proton recoil and so an
extrapolation to q = 0 is needed. One fits the q2 f 0 data with a form factor, in
(1 + Q2/MA)2 '
where MA is a mass scale to be fitted. Other experiments have determined this to
have the value MA = 1.032 0.036 GeV. If ron fixes MA to equal the world aver-
age, then es = -0.15 0.09; hence the claim to support the nonzero strange
polarization. However, Ref. 32 also makes another, less well-advertised, fit.
They constrain es = ; and find that in this case es = 0; MA = 1.06 0.05 GeV.
Thus, one seas that es = 0 yields MA consistent with the world average and hence
is equally acceptable as a solution. The crucial statement in Ref. 32 is that "MA
and n(As) are strongly correlated". Thus, Ref. 32 does not require es < 0 and
thereby does not necessarily lend support to those who desire es * 0. Thus the
question of the magnitude of the (strange) sea polarization is open. It is likely
to be significantly nearer to zero than is being assumed in much of the current
literature. Some of the inferences claimed from the EMC polarization data may
need re-evaluation therefore. In particular, there need be no conflict with per-
turbative quantum chromodynamics.30
3.3. Polarized Gluons?
It has recently been realized8 that the perturbative QCD correction to the
singlet part of gi(x) effectively scales (to 0(as2)) and may be important. This
may be incorporated by replacing the Aq in Section 1 by aq eq - as/2n eG, where
eG a ! dxeg(x) and eG(x) = gt(x) - G+(x) is the polarized gluon distribution.
This modifies the polarized lepton analysis, but cancels out in the expressions
for (gA/IV) and does not enter the magnetic moment (Section 2) analysis.
One consequence is that there may be a continuity between the low-energy
polarization revealed in constituent quarks (magnetic moments and spin dependence
of resonance excitation) and the deep inelastic polarization.
First of all, we summarize the data ni the eq (or equivalently Eq) from the
If we assume SU(3)F symmetry in the sense that s(E+) . d(P), then we may
write the various gA in terms of F, D, or eq as follows:
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Close, F. E. Quarks and gluons in hadrons and nuclei, article, December 1, 1989; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1058782/m1/21/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.