Motivation (continued) polarized p-p

The measured quark spin-structure functions in the proton sum to less than the required spin-1/2: the 'spin crisis'. One possibility is that the gluons carry the missing spin.
PHENIX currently has limited existing capability to adress this question for x>0.05, using direct photons approximately opposite a high-pT hadron. This x-range is not broad enough to address the spin crisis.
The silicon vertex upgrade detector can extend the range to 0.002<x<0.4, measuring the spin asymmetry of open charm and open beauty.

The measured quark spin-structure functions in the proton sum to less than the required spin-1/2: the 'spin crisis'. One possibility is that the gluons carry the missing spin.