In QCD physics, certain partonic distributions like Generalized Parton Distributions (GPDs) and Transverse Momentum Distributions (TMDs) are defined for the case where the parton is either unpolarized, longitudinally polarized or transversely polarized. But how can the parton be polarized or unpolarized? I understand that quarks are spin 1/2 particles (and spin-1 for gluons), but typically to polarize electrons or nuclei in scattering experiments, experimentalists increase the polarization using techniques such as optical pumping for target nuclei. But what determines whether a parton is polarized?
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$\begingroup$ partons is a name covering quarks and gluons. en.wikipedia.org/wiki/… quarks have charge and spin and can be polarized in a mathematical model. $\endgroup$– anna vCommented Aug 22, 2023 at 4:13
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$\begingroup$ Sure but I'm talking experimentally. For example, the Boer-Mulders function probes a transversely polarized quark in an unpolarized nucleon. But how does one design an experiment to probe transversely polarized quarks? $\endgroup$– coopdog218Commented Aug 23, 2023 at 5:30
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$\begingroup$ The design would be more complicated than for detecting quarks to start with. for example see how experiments detect quark versus gluon jets cds.cern.ch/record/2254861/files/1512294_73-78.pdf . it is not simple $\endgroup$– anna vCommented Aug 23, 2023 at 8:05
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