– 1– DEVELOPMENTS IN HEAVY QUARKONIUM SPECTROSCOPY

A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of re-lated experimental activity. The subsequent broad spectrum of breakthroughs, surprises, and continuing puzzles had not been anticipated. In that period, the BESII program concluded only to give birth to BESIII; the B-factories and CLEO-c flour-ished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC opened a window on the deconfinement regime. For an extensive presentation of the status of heavy quarkonium physics, the reader is referred to several reviews [1–7], the last of which covers developments through the middle of 2010, and which supplies some tabular information and phrasing repro-duced here (with kind permission, copyright 2011, Springer). This note focuses solely on experimental developments in heavy quarkonium spectroscopy, and in particular on those too recent to have been included in Ref. 7. Table 1 lists properties of newly observed conventional heavy quarkonium states, where “newly ” is interpreted to mean within the past decade. The hc is the 1P1 state of charmonium, singlet partner of the long-known χcJ triplet 3PJ. The ηc(2S) is the first excited state of the pseudoscalar ground state ηc(1S), lying just below the mass of its vector counterpart, ψ(2S). The state originally dubbed Z(3930) is now regarded by many as the first observed 2P state of χcJ, the χc2(2P). The first B-meson seen that contains charm is the B+c. The ground state of bottomonium is the ηb(1S), recently confirmed with a second observation of more than 5σ significance. The Υ(1D) is the lowest-lying D-wave triplet of the bb ̄ system. Both the hb(1P), the bottomonium counterpart of hc(1P), and the next excited state, hb(2P), were very recently observed b