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spin structure of the proton

The surprising results of the polarized muon scattering off the polarized proton reported by the EMC collaboration have stimulated both experimental and theoretical works to elucidate the spin structure of the proton. The fraction of the proton spin carried by quark, , was amazingly small comparing to the canonical expectation 0.600.12 [1]. The current best guess is:

Current knowledge on the quark polarization in the proton is summarized in Table 1.

  
Table 1: Summary of the experimental results and some theoretical predictions on the quark polarization in the proton.

As a result of extensive efforts, those works nearly converge into two possible solutions of the proton spin puzzle:

Those are not directly measured in polarized deep-inelastic scattering (pol-DIS) experiment since gluon does not couple directly to the photon; and photon couples to the quark and to the anti-quark in a same way. In the case of pp collisions, there are several processes where gluons participate directly, such as prompt photon production and heavy quark production. The presence of the anti-quark contribution is obvious in Drell-Yan productions (, W, ). Furthermore, flavor decomposition of quark and anti-quark polarization can be confirmed in W-production. The measurements of and will contribute much to understanding the spin structure of the proton. Such measurements will be discussed after a brief description of PHENIX detector system in the next section.




next up previous
Next: PHENIX Detector System Up: Spin Physics Program Previous: Spin Physics Program

Naohito Saito
July 3, 1996