Quarks and gluons in hadrons and nuclei Page: 25 of 31
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where f(r12) was assumed to be A independent. Qualitatively, the effect is driven
by the chance that there is a nearby nucleon correlated with the target nucleon.
Reference 4 made a geometrical model for g2 and predicted bF2 for all A. (As the
volume of a nucleon is only about 40% of the available volume, the two-nucleon
contribution is < 10% effect, and three-body and higher contributions can be
ignored.) The fit is excellent and shows that the EMC effect is sensitive to
details of nuclear structure, reflected in pA(r) as a result of which significant
fluctuations are predicted at small A which have yet to be studied. At large A
the behavior is smooth and it is safe to interpolate. Thus, one can infer the
FA(x) when A = tungsten, say, and use this as input to nW + uP ... analyses for
A common feature of models is that the degradation of the valence quarks
transfers energy momentum to some other component (gluons and qq in rescaled QCD44
or the partons in the n that are responsible for nuclear binding).4s,46 Thus,
they generate an increased sea in nuclei relative to that measured in free
nucleons. In turn, this implies that FA/FN > 1 as x + 0. However, this predicted
enhancement will probably be blacked out by shadowi ,g (which has not been incor-
porated in these models so fart. Mueller and Qiu42 have begun to illuminate us
about the x and Q2 dependence of nuclear shadowing; the quail titative combination
of their work with "soft "45,45 or rescaled QCD42,44 remains to be completed.
What impact does this have on Drell-Yan?
If xl 2 refers to the beam and target partcns, xF = xl - x2, and X1X2 = Q2/s,
then the ratio of cross sections for some fixed Q2/s is
bA qb (xl)qA (x2) + qb (x1)}A (2}
S qb (x1)q (x2) + qb (xq (x2)
where sum over flavors weighted by their squared charge is understood. In the
case of i- beams, if x2 > 0.2 so that qA qA, the DY process is dominantly due
to qn annihilating with qAN. Thus, in this kinematic regime
o-A uA (x2) FA(x2)
on-N ~ uN (x N 2(x
This is the same ratio as measured in inelastic lepton scattering ("EMC effect")
and must be obtained here too if factorization is valid. Thus, we should not be
surprised by the results from NA1047 who study
and by varying Q2 and xF can separate both the pion and target structure func-
tions. In Ref. 47 they exhibit the resulting ratio of qA /qN(x2) and
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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/m1/25/: accessed March 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.