A non-vanishing Sivers function for the sea quarks is evidence there is sea quark orbital angular momentum (OAM).
If sea-quark Sivers asymmetry is non-zero, then sea quarks have non-zero OAM.
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The gauge invariant definition of the Sivers function predicts the opposite sign for the Sivers function in SIDIS compared to processes with color charges in the initial state and a colorless final state such at Drell-Yan and W/Z boson production. In W/Z production, it is guaranteed that an anti-quark is involved as in Drell-Yan process.
SpinQuest will explore properties of the nucleon's spin composition by investigating correlation of the light antiquarks motion relative to the nucleon spin.
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SpinQuest can testing the interplay between time-reversal symmetry and gauge symmetry: This can be understood by applying time-reversal to the quark fields in the operator definitions of the parton densities and how the gauge link provide the phase for the interference. The Sivers asymmetry is manifest like other naive T-odd observables because one is not integrating in such a measurement over transverse momentum.
SpinQuest is attempting to push the proton beam intensity frontier on a solid polarized target (specifically instantaneous intensity).
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