Optimal spin-quantization axes for quarkonium with large transverse momentum

Understand

The gluon collision process that creates a heavy-quark-antiquark pair with small relative momentum and large transverse momentum predicts at leading-order in the QCD coupling constant that the transverse polarization of the pair should increase with its transverse momentum.

• Measurements at the Fermilab Tevatron of the polarization of charmonium and bottomonium states with respect to a particular spin-quantization axis are inconsistent with this prediction.
• However the predicted rate of approach to complete transverse polarization depends on the choice of spin-quantization axis.
• We introduce axes that maximize and minimize the transverse polarization from the leading-order gluon collision process.