Nucleon Spin Structure Study at Jefferson Lab Page: 2 of 38
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both theoretical [3] and experimental physicists devoted substantial efforts
to understand this problem. A new generation of experiments were carried
out at SLAG (E142, E143, E154, E155 and E155x) [4], CERN (SMC) [5] and
DESY (HERMES) [6]. These experiments concluded that the quark carries
about 20 - 30% of the nucleon spin, and the Bjorken sum rule [7] is verified
to about 7% level. The next section is an overview of the current status of
the spin structure study.
At the Q2 = 0 end, there is another related sum rule for spin structure,
the Gerasimov-Drell-Hearn (GDH) sum rule [8]. Large efforts have been put
and are planned to test the GDH sum rule and to study the spin structure
in the resonance region. In section 3, preliminary results from Mainz are
presented as well as the future plans of Jefferson Lab and other laboratories.
To connect the GDH with the Bjorken sum rule, several attempts were
made to extend the GDH sum rule. One of the generalized GDH sum rule
derivation will be presented in Section 4. A large number of experimental
efforts are underway at Jefferson Lab, which is a 100% duty factor 6 GeV
electron accelerator with high luminosity. The recent progress in the polar-
ized electron source and polarized proton, deuteron and 3He targets greatly
extends the kinematic region for the study of the nucleon spin structure.
First preliminary extended GDH experiment results with virtual photon are
presented and discussed in Section 4.
Taking advantage of the high luminosity (1036 particles/sec for polarized
beam-polarized target), experiments are planned at Jefferson Lab to study
polarized valence quark structure with DIS in the high x region. As an
example, one experiment, which will measure the neutron spin asymmetry
(Ai), is discussed in Section 6.
Experiments are also planned to study effects beyond the leading twist.
The leading twist gives the quark distributions in the nucleon. The higher
twists give access to the quark-gluon interactions. As an example, one ex-
periment will measure the g2 spin structure function. The deviation of g2
from the leading twist part g2'"', which can be obtained from the measured gi
structure function, gives the twist 3 and higher twist contributions. Details
are given in Section 7.
An energy upgrade to 12 GeV is planned for Jefferson Lab. Nucleon spin
structure study with the upgraded Jefferson Lab is discussed in Section 8.2
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Chen, Jian-ping. Nucleon Spin Structure Study at Jefferson Lab, article, November 8, 2000; Newport News, Virginia. (https://digital.library.unt.edu/ark:/67531/metadc725566/m1/2/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.