Hybrid mesons

Abstract

A review of the theoretical and experimental status of hybrid hadrons is presented. The states π 1 (1400), π 1 (1600), and π 1 (2015) are thoroughly reviewed, along with experimental results from GAMS, VES, Obelix, COMPASS, KEK, CLEO, Crystal Barrel, CLAS, and BNL. Theoretical lattice results on the gluelump spectrum, adiabatic potentials, heavy and light hybrids, and transition matrix elements are discussed. These are compared with bag, string, flux tube, and constituent gluon models. Strong and electromagnetic decay models are described and compared to lattice gauge theory results. We conclude that while good evidence for the existence of a light isovector exotic meson exists, its confirmation as a hybrid meson awaits discovery of its iso-partners. We also conclude that lattice gauge theory rules out a number of hybrid models and provides a reference to judge the success of others.

Some aspects of three-quark potentials

“…One of the important differences between QCD and AdS/CFT is that QCD has got much further than AdS/CFT in addressing the issue of hybrid potentials [15]. The common wisdom is that those potentials correspond to excited strings [5].…”

“…A simple estimate using (2.11) and the fitted value of κ shows that [18] 15) where α QQ is a coefficient in front of the Coulomb term of the quark-antiquark potential [22]. Explicitly, it is given by α QQ = (2π…”

“…So far, there are no phenomenological predictions and very little is known about those from lattice studies. 3 These potentials remain almost unknown and, therefore, merit more attention, as in the case of the hybrid quark-antiquark potentials [8,15].…”

Amplitude analysis of the χc1→ηπ+π− decays

“…Several candidates with J P C = 1 −+ , decaying into different final states, such as ηπ, η ′ π, f 1 (1270)π, b 1 (1235)π and ρπ, have been reported by various experiments, and these have been thoroughly reviewed in Ref. [1]. The lightest exotic meson candidate is the π 1 (1400) [2], reported only in the ηπ final state by GAMS [3], KEK [4], Crystal Barrel [5], and E852 [6], but its resonance nature is controversial [7].…”

Light-quarkonium spectra and orbital-angular-momentum decomposition in a Bethe–Salpeter-equation approach

“…The OAMD for the two lowest-lying 1 −+ is very similar to the 1 −− case. While the identification of these two 1 −+ states with the experimental π 1 (1400) and π 1 (1600) is debatable, e. g., [86,151,152], we find a predominantly S-wave ground state and a D-wave first excitation. The K * (892) looks very similar to the ρ as well, which is not surprising, given the context of SU (3) flavor symmetry in QCD.…”