Heavy quarkonia: the beauty and the beasts

Abstract

New enhancements in the charmonium and bottomonium spectra observed since 2003 are very briefly reviewed. Special attention is paid to χc1(3872) (formerly X(3872)) owing to its remarkable proximity to theD 0 D 0 threshold, which allows modelling as a quasibound axial-vector cc state with a largeD 0 D 0 admixture. In contrast, the interpretation of many other charmonium-like and bottomonium-like states is still very controversial and some may not even correspond to genuine resonances. Accordingly, several entries in the PDG tables have been wildly changing over the years. Three representative states are reviewed here as non-resonant enhancements due to threshold effects, viz. ψ(4260), ψ(4660), and Υ(10580).

Modern meson spectroscopy: the fundamental role of unitarity

“…Finally, we discuss a bottomonium state that is generally believed to be very well established, namely Υ(10580), which has been included in the PDG tables for many years and is listed [10] as Υ(4S). However, we interpreted [40,140,141] it rather as a non-resonant bump right between the BB and BB thresholds. The crucial point is that the data [142] show a small yet clear enhancement on top of the B s Bs threshold, whereas there are unmistakable dips at the openings of the B B and B B thresholds (see Fig.…”

“…( 41) are determined with the variance formula, given the data spreading for the real and imaginary parts of the pole positions shown in Eqs. (39,40), instead of simply [17] from those PDG limits. The conclusion is that the PDG seems to underestimate the BW masses of both f 0 (500) and K 0 (700), as well as the BW width of K 0 (700).…”

“…For an overview of the rapidly expanding and changing PDG listings of hidden-charm and hidden-bottom states between 2002 and 2018, see Ref. [40].…”