Abstract
We propose a new schematic model for mesons in which the building blocks are quarks and flavor-antisymmetric diquarks. The outcome is a new classification of the entire meson spectrum into quark–antiquark and diquark–antidiquark states which does not give rise to a radial quantum number: all mesons which have so far been believed to be radially excited are orbitally excited diquark–antidiquark states; similarly, there are no radially excited baryons. Further, mesons that were previously viewed as “exotic” are no longer exotic as they are now naturally integrated into the classification as diquark–antidiquark states. The classification also leads to the introduction of isorons (iso-hadrons), which are analogs of atomic isotopes, and their magic quantum numbers, which are analogs of the magic numbers of the nuclear shell model. The magic quantum numbers of isorons match the quantum numbers expected for low-lying glueballs in lattice QCD. We observe that interquark forces in mesons behave substantially differently from those in baryons: qualitatively, they are color–magnetic in mesons but color–electrostatic in baryons. We comment on potential models and the hydrogen atom. The implications of our results for confinement, asymptotic freedom, and a new set of relations between two fundamental properties of hadrons—their size and their energy—are discussed in our companion paper (Eur. Phys. J. C (2013). doi:10.1140/epjc/110052-013-2299-8).
Highlights
It is well-known that making reliable predictions about low-energy QCD and hadrons is a great challenge, as perturbative methods of quantum field theory do not apply at low energies where the coupling constant is strong
The common approach has been to propose various dynamical models which are inspired by assumptions, ideas, and intuition borrowed from physical systems, such as atomic physics and non-relativistic quantum mechanics, which are not QCD
A few mesons have been viewed as having diquarks as constituents – to name just two examples, the light scalar mesons were interpreted as diquark-antidiquark states [11], as were several charmed and hidden-charm mesons [12, 13]
Summary
It is well-known that making reliable predictions about low-energy QCD and hadrons is a great challenge, as perturbative methods of quantum field theory do not apply at low energies where the coupling constant is strong. [01/28 08:45] Special, APS, Numbered, rh:Standard diquark configurations, selected for us by the flavor structure of meson phenomenology, are building blocks for mesons in addition to and on equal footing with the quarks of the traditional quark model. While our results may appear counterintuitive, they are completely consistent with the known properties of QCD, such as confinement and asymptotic freedom, and provide a novel [01/28 08:45] Special, APS, Numbered, rh:Standard explanation for the relation between them. We discuss this in our companion paper [1].
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