Quarks and gluons in hadrons and nuclei Page: 29 of 31
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The NA(10) data"7 on n' W/D +u- ... may give hints that we are right to be
wary of E537. Recall their extracted quark ratio which is in line with the EMC
data from inelastic muon scattering - "EMC effect".41 This is fine for the
140-GeV and 286-GeV Data combined, but when one looks at the NA(10) data 140 GeV
sample alone, things are less clear. The xF distribution from NA(10) (which is a
convolution of beam and target and thus "nearest" to the E537) for 140 GeV matches
smoothly onto E537 at x = 0.2 - and the reason is that q"(W) * q!(Be) in the
140-GeV data sample. I have no idea why this should be so, but if it is true for
gluons too that g( * g (Be) at 125 GeV, then it raises a question about extrac-
tion gW (x)gBe(x) from E537. If we take the NA(10) data on quarks as a guide,
then it is possible that the gW/Be(x) is, in effect, to be renormalized upwards by
20%. (More legitimately, I don't know why there is such an energy dependence, or
even if it is real, but I would be happier to see the E537 experiment with 300 GeV
incident beams or comparison with T production so as to get some lever on the xlx2
If one renormalizes the ratio in Fig. 2 upwards by 20%, then there is no
shadowing at x 0.2 and, furthermore, the data then look quantitatively as expec-
ted in Mueller-Qiu theory of shadowing.2 It is important that this problem with
separation be better understood before we can conclude very much on the g (x)
ratio. (Another reason why one might regard this renormalization as reasonable is
that "infinite" shadowing leads to an A2/3 behavior and for W/Be ratio this is
0.37. The trend of the E537 data looks set to violate this, whereas a 20%
increase would bring this into line.)
Experiment E672 at Fermilab is measuring53 i-A + 4 on four nuclei at 530 GeV.
I await their "high energy" extraction of gA/N(x). Until the conundrum of energy
dependence (i.e. the non-factorization of the partons in the incident beam) is
settled, I conclude that gA/N(x) probably falls as x + 0, in qualitative agreement
with the shadowing phenomenon, but the quantitative measure is unclear.
Thus, with the exception of valence quarks for x > 0.2, there is little or no
evidence for non-trivial behavior for qA/N and gA/N. It is imperative to know
these quantities much better, and to understand the anomalous energy dependence
manifested by NA(10), and implicitly hinted at by E537. Until we do, then we can-
not, with any confidence, use J/ , relative to Drell-Yan production in AA colli-
sions as a signal for quark-gluon plasma formation. Note that if the E537 experi-
ment's dramatic suppression of nuclear glue is true, then 4 production per nucleon
in heavy-ion collisions will be markedly suppressed relative to that in pp or even
pA interactions. There is no'reason to anticipate such drama for Drell-Yan.
Here’s what’s next.
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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/m1/29/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.