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The first measurement of the sea quark Sivers function is not SpinQuest but has been performed by the Star collaboration at RHIC using W/Z boson production rather than Drell-Yan. https://arxiv.org/pdf/1511.06003.pdf
SpinQuest will perform the first measurement of the Sivers asymmetry in Drell-Yan pp scattering from the sea quarks.
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.
We can say: SpinQuest will perform the first measurement of the Sivers asymmetry in Drell-Yan pp scattering from the sea quarks.
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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