Quarkonium spectroscopy and perturbative QCD: a new perspective

We study the energy spectrum of bottomonium in perturbative QCD, taking αs(MZ)=0.1181±0.0020 as input and fixing mbMS(mbMS) on the ϒ(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 nonperturbative effects. A new qualitative picture on the structure of the bottomonium spectrum is provided. The lowest-lying cc̄ and bc̄ states are also examined.