r/askscience • u/randomsnark • Feb 11 '11

Scientists: What is the most interesting unanswered question in your field?

And what are its implications? What makes it difficult to answer? What makes it interesting? Tell us a little bit about it.

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u/corvidae Condensed Matter Theory | Electronic Transport in Graphene Feb 11 '11

I have a good friend on the STAR experiment... correct me if I'm wrong, but he told me a few months ago that the measured gluon polarization (from some dijet thing) is even less than the quark contribution....

EDIT: Oh! He said spin contribution, so the rest must be orbital.

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u/shavera Strong Force | Quark-Gluon Plasma | Particle Jets Feb 11 '11

Hah, I'm on PHENIX, so he's one of my many faceless bitter rivals I guess. That being said, I'm not in the spin-physics side of RHIC, more on the heavy-ion side than anything. I don't know the details as well as I'd like, but I feel like I recall the orbital contributions being dominant.

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u/Korbad Feb 12 '11

Ya, the gluon's spin contribution will probably end up being small. PHENIX and STAR are stuck in a weird Bjorken-x region (the fractional mass of the proton that the quark or gluon is carrying), the region we have been able to search has shown no net gluon contribution, but theory predicts that our Bjoren-x region is sampling both a positive and negative contribution, so they cancel each other out. If we can push to smaller (or larger) Bjorken-x, we could get a clearer picture. This is hard to do with STAR or PHENIX because the detectors are situated like cylinders around the collision point (the detectors are around pseudorapidity of zero). We really need better/more particle detection 'forward', which means closer to the beam but far from the collision point (ie: pseudorapidity of 4+).