Systematic studies of charmonium-, bottomonium-, and Bc -like tetraquark states

Abstract

We study the mass splittings of Q1q2Q3q4 (Q = c, b, q = u, d, s) tetraquark states with chromomagnetic interactions between their quark components. Assuming that X(4140) is the lowest J P C = 1 ++ cscs tetraquark, we estimate the masses of the other tetraquark states. From the obtained masses and defined measure reflecting effective quark interactions, we find the following assignments for several exotic states: (1) both X(3860) and the newly observed Zc(4100) seem to be 0 ++ cncn tetraquarks; (2) Zc(4200) is probably a 1 +− cncn tetraquark; (3) Zc(3900), X(3940), and X(4160) are unlikely compact tetraquarks; (4) Zc(4020) is unlikely a compact tetraquark, but seems the hidden-charm correspondence of Z b (10650) with J P C = 1 +− ; and (5) Zc(4250) can be a tetraquark candidate but the quantum numbers cannot be assigned at present. We hope further studies may check the predictions and assignments given here.

New charged resonance $$Z_{c}^{-}(4100)$$ Z c - ( 4100 ) : the spectroscopic parameters and width

“…The conclusion about a tetraquark nature of Z c with quantum numbers J PC = 0 ++ was drawn in Ref. [18] as well. In the hadrocharmonium framework the resonances Z c and Z − c (4200) were treated as the scalar η c and vector J/ψ charmonia embedded in a light-quark excitation with quantum numbers of a pion [19].…”

“…Therefore, one can consider Z c as the groundstate scalar or vector tetraquark with ccdu content. The recent theoretical articles devoted to the Z c resonance are concentrated mainly on exploration of its spin and possible decay channels [17][18][19][20][21]. Thus, sum rule computations carried out in Ref.…”

QCD sum rules approach to the X, Y and Z states

“…In Ref. [330] the authors used a simple chromomagnetic model to study the mass splitting among tetraquark states, including Z − c (4100). The model is based on the description that the mass splitting among hadron states, with the same quark content, are mainly due to the chromomagnetic interaction term in the one-gluon-exchange potential.…”

Exotic pentaquark states with the qqQQQ¯ configuration

“…Mesons Baryons Baryons Using the mass formula M = i M i + H CMI and the obtained parameters, one sees that the estimated masses of conventional hadrons are in general higher than the measured values, which is illustrated in Table V. The reason is that the adopted model and parameters could not account for the necessary attractions for all the hadrons. Overestimated masses with this approach were also obtained in various tetraquark and pentaquark states [83][84][85][86][87][88][89][90]. To make a more reasonable estimation, we use the improved mass formula by replacing i M i in Eq.…”

“…When the spacial contributions are encoded into effective quark masses and coupling parameters, the Hamiltonian can be written as the form containing just the quark mass term and the color-spin interaction term and one gets the CMI model. There are many studies about the mass spectrum for multiquark systems within this model [83][84][85][86][87][88][89][90][91]. The qualitative properties of the obtained spectra are helpful for us to search for relevant exotic states.…”