Gluonic excitations' millennial finale

Abstract

We provide an overview of theoretical developments on hybrid mesons and glueballs in the last year at this turn of the millenium conference. Cracks in potential models of conventional mesons are developing. Hybrid meson adiabatic surfaces have been calculated and interpreted, experimental J P C exotics have hybrid meson, four-quark state or nonresonant interpretations, and the strong decay mechanism of hybrids has been studied. All theoretical progress on hybrid mesons in the last year is mentioned. Overall features of glueballs are visited: decays and the successes of the large N c limit. Two promising experimental areas are mentioned: charmonium hybrids at B-factories and ss hybrids at Jefferson Lab. Cracks in Potential Models: Radial ExcitationsThere are three mass regions in which in which there are recent experimental indications for states at masses inconsistent with potential model predictions:• Crystal Barrel, VES, ARGUS and L3 [1] have evidence for a 2 (1660) approximately 170 MeV lower than potential model expectations [2].

Hybridgen: A Model for the Study of QCD Hybrid States

“…The eigenvalue is determined by the boundary condition ψ(r = R) = 0 (7) appropriate to this nonrelativistic analysis. 3 We solve this transcendental equation for the eigenvalue, n 0 , numerically. The results are shown in the Table. Note that the numerical solution shows that, for x 0 > 3, the difference between the eigenvalue in the cavity and the continuum limit is already ≤ 6%.…”

“…These lattice data [2] provide a standard with which all models may be compared (for a concise review see, e.g., [3]). At small quark separation, lattice data are reasonably well described by bag models [4].…”

“…Masses of physical states can then be found in the leading Born-Oppenheimer approximation, at least for very heavy quarks. These lattice data [2] provide a standard with which all models may be compared (for a concise review see, e.g., [3]). At small quark separation, lattice data are reasonably well described by bag models [4].…”

“…Physically, the transverse glue in the hybrid constitutes a valence particle. This approach is not applicable at large separation, where flux tube models [5] and string pictures [7] seem to provide a better description [3] in terms of oscillation mode excitations of the string or the tube. Earlier constituent gluon models generally do not agree with the lattice mass predictions [8].…”