Quarkonium Spectroscopy and Perturbative QCD: A New Perspective

We study the energy spectrum of bottomonium in perturbative QCD, taking $\als(M_Z)=0.1181 \pm 0.0020$ as input and fixing $m_b^{\bar{\rm MS}}(m_b^{\bar{\rm MS}})$ on the $\Upsilon(1S)$ mass. Contrary to wide beliefs, perturbative QCD reproduces reasonably well the gross structure of the spectrum as long as the coupling constant remains smaller than one. We perform a detailed analysis and discuss the size of non-perturbative effects. A new qualitative picture on the structure of the bottomonium spectrum is provided. The lowest-lying $c\bar{c}$ and $b\bar{c}$ states are also examined.