Heavy quarkonium in a weakly-coupled quark-gluon plasma below the melting temperature

We calculate the heavy quarkonium energy levels and decay widths in a quarkgluon plasma, whose temperature T and screening mass m_D satisfy the hierarchy mα_s » T » mα² _s » m_D (m being the heavy-quark mass), at order mα_s⁵. We first sequentially integrate out the scales m, mα_s and T, and, next, we carry out the calculations in the resulting effective theory using techniques of integration by regions. A collinear region is identified, which contributes at this order. We also discuss the implications of our results concerning heavy quarkonium suppression in heavy ion collisions.