I just came back from the Division of Nuclear Physics meeting of the APS where I could show our first data on beam spin asymmetries from hadron pairs:
This plot shows the asymmetry vs. x Bjorken (roughly the momentum that the struck quark carries of the parent nucleon). There is a very suggestive rise of the measurement that can be interpreted as the force that the gluons exert on a transversely polarized quark as it moves through the proton after being struck.
This is quite interesting since it open up a window to quark-gluon interactions inside the proton and because our understanding is that quarks can only have transverse polarization in an unpolarized nucleon if they also carry transverse momentum (Boer-Mulders effect).
More background can be found in my recent write-up here: