Multiquark States

Abstract

Why do we see certain types of strongly interacting elementary particles and not others? This question was posed more than 50 years ago in the context of the quark model. M. Gell-Mann and G. Zweig proposed that the known mesons were [Formula: see text] and baryons qqq, with the quarks known at the time, u (up), d (down), and s (strange), having charges of 2/3, −1/3, and −1/3, respectively. Mesons and baryons would then have integral charges. Mesons such as [Formula: see text] and baryons such as [Formula: see text] would also have integral charges. Why weren't they seen? They have now been seen, but only with additional heavy quarks and under conditions that tell us a lot about the strong interactions and how they manifest themselves. This review describes recent progress in our understanding of such exotic mesons and baryons.

Disclosing $$D^*\bar{D}^*$$ D ∗ D ¯ ∗ molecular states in the $$B_c^- \rightarrow \pi ^- J/\psi \omega $$ B c - → π - J / ψ ω decay

“…As commented in Ref. [3] the support for hadron molecules is quite obvious once we realize that baryon molecules exist in the form of nuclei. In fact, multimesons states, not just meson-meson molecules, have also been advocated, like multi-rho states in Ref.…”

“…The identification of states as being of molecular nature is not an easy task, and in general standard quark structures, or multiquark states are competing in the interpretation [1,3]. Yet, there are several experimental features that reveal the molecular structure [2] and ultimately it is the systematic and correct description of experimental features and the accuracy of the predictions what builds up in favor of this structure for many states.…”

Spectrum of p -wave hidden-charm exotic mesons in the diquark model

“…[23] and fixing as an initial point the value of the multiplet-average mass M 0 (1S) from Eq. (8). Using the latter approach, and depending upon which specific lattice simulation is used to obtain the Σ + g BO potential, one obtains M 0 (1P ) = 4358-4361 MeV .…”

“…The value of κ qQ obtained actually turns out to be smaller than the value obtained in Eq. (8) for the 1S multiplet.…”

“…rises somewhat-still providing a good fit-but most significantly, κ qQ becomes almost equal to the value in Eq. (8). If one then also attempts to fit to P Y (4230)…”