Radiative and Meson Decays of Y(4230) in Flavor SU(3)

The charmonium-like exotic states Y(4230) and the less known Y(4320), produced in e+e− collisions, are sources of positive parity exotic hadrons in association with photons or pseudoscalar mesons. We analyze the radiative and pion decay channels in the compact tetraquark scheme, with a method that proves to work equally well in the most studied D∗→γ/π+D decays. The decay of the vector Y into a pion and a Zc state requires a flip of charge conjugation and isospin that is described appropriately in the formalism used. Rates are found to depend on the fifth power of pion momentum, which would make the final states πZc(4020) strongly suppressed with respect to πZc(3900). The agreement with BES III data would be improved considering the πZc(4020) events to be fed by the tail of the Y(4320) resonance under the Y(4230). These results should renovate the interest in further clarifying the emerging experimental picture in this mass region.

Four-quark matter—a new era of spectroscopy

In 1964, both Gell-Mann and Zweig proposed the famous Quark Model in particle physics, which tells us hadrons are built of three quarks (baryons) or quark anti-quark pair (mesons). However, the theory of strong interaction—QCD—allows the existing of hadrons beyond the conventional baryon and meson picture. These new hadron states are called exotic hadrons, and have been searched for over the past half century. In this review, I will introduce you the discovery of a new particle called Zc(3900), which is considered as the first convincing four-quark particle. The observation of four-quark matter gains great interest in particle physics, and triggered subsequent intensive study of exotic hadrons, which brings us to a new era of hadron spectroscopy and refreshes our knowledge about the hadronic matter in our universe.

Deciphering the recently discovered tetraquark candidates around 6.9 GeV

Recently a novel hadronic state of mass 6.9 GeV, that decays mainly to a pair of charmonia, was observed in LHCb. The data also reveals a broader structure centered around 6490 MeV and suggests another unconfirmed resonance centered at around 7240 MeV, very near to the threshold of two doubly charmed $$\Xi _{cc}$$ Ξ cc baryons. We argue in this note that these exotic hadrons are genuine tetraquarks and not molecules of charmonia. It is conjectured that they are V-baryonium , namely, have an inner structure of a baryonic vertex with a cc diquark attached to it, which is connected by a string to an anti-baryonic vertex with a $${\bar{c}} {\bar{c}}$$ c ¯ c ¯ anti-diquark. We examine these states as the analogs of the V-baryonium states $$\Psi (4360)$$ Ψ ( 4360 ) and Y(4630)/$$\Psi (4660)$$ Ψ ( 4660 ) which are charmonium-like tetraquarks. One way to test these claims is by searching for a significant decay of the state at 7.2 GeV into $$\Xi _{cc}{\overline{\Xi }}_{cc}$$ Ξ cc Ξ ¯ cc . Such a decay would be the analog of the decay of the state Y(4630) into to $$\Lambda _c{\overline{\Lambda }}_c$$ Λ c Λ ¯ c . We further argue that there should be trajectories of both orbital and radial excited states of the X(6900). We predict their masses. It is possible that a few of these states have already been seen by LHCb.