Regge amplitude fit to high-energy polarized pi- Delta++ photoproduction confirms pion dominance at small t and extracts pi N Delta coupling consistent with Delta decay plus first values for rho, b1, and a2 N Delta couplings.
Hybrid Mesons
5 Pith papers cite this work. Polarity classification is still indexing.
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abstract
A review of the theoretical and experimental status of hybrid hadrons is presented. The states $\pi_1(1400)$, $\pi_1(1600)$, and $\pi_1(2015)$ 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.
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Using the fixed-center approximation, the π⁰(η) f₁(1285) interaction yields scattering parameters and correlation functions but no clear poles for the π₁(1400), π₁(1600), or η₁(1855) resonances, only a broad structure near 1500-1600 MeV and a cusp at the η f₁ threshold.
Charmed-meson loop calculations reproduce the branching fractions of chi_cJ to eta eta eta' and the absence of eta1(1855) signal in the eta eta' spectrum.
Simulations reveal substantial differences in transverse momentum spectra between compact T_cc tetraquarks formed at partonic level and molecular X(3872) states formed at hadronic level, plus production asymmetry and source-characterizing coalescence parameters.
A constituent quark model predicts masses of 1.9, 4.2, and 6.6 GeV for light, charmonium-like, and fully-charm 1^{-+} tetraquarks along with decay ratios for specific two-body channels and rules out η1(1855) as a compact tetraquark.
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Systematic study of exotic $1^{-+}$ tetraquark spectroscopy
A constituent quark model predicts masses of 1.9, 4.2, and 6.6 GeV for light, charmonium-like, and fully-charm 1^{-+} tetraquarks along with decay ratios for specific two-body channels and rules out η1(1855) as a compact tetraquark.