Glueballs, Hybrids, Multiquarks. Experimental facts versus QCD inspired concepts

Analysis of Y(2175) as a tetraquark state with QCD sum rules

In this article, we assume that there exists a scalar hidden charm tetraquark state in the π+χc1 invariant mass distribution, and we study its mass using the QCD sum rules. The numerical result MZ=(4.36±0.18) GeV is consistent with the mass of the Z(4250). The Z(4250) may be a tetraquark state, but other possibilities, such as a hadro-charmonium resonance and a $D_{1}^{+}\bar{D}^{0}+D^{+}\bar{D}_{1}^{0}$ molecular state, are not excluded.

Another tetraquark structure in the π+χc1 invariant mass distribution

Ds0(2317) as a tetraquark state with QCD sum rules in heavy quark limit

In this article, we assume that there exist hidden charmed tetraquark states with spin–parity J
 P=1−, and we calculate their masses with the QCD sum rules. The numerical result indicates that the masses of the vector hidden charmed tetraquark states are about M
 Z
 =(5.12±0.15) GeV or M
 Z
 =(5.16±0.16) GeV, which are inconsistent with the experimental data on the π
 +
 χ
 c1 invariant-mass distribution. The hidden charmed mesons Z
 1, Z
 2 or Z may be scalar hidden charmed tetraquark states, hadro-charmonium resonances or molecular states.

Possible tetraquark states in the π + χ c1 invariant-mass distribution

In this article, we take the point of view that the scalar mesons $ f_0(980)$ and $a_0(980)$ are diquark-antidiquark states $(qq)_{\bar{3}}(\bar{q}\bar{q})_3$, and devote to determine their masses in the framework of the QCD sum rules approach with the interpolating currents constructed from scalar-scalar type and pseudoscalar-pseudoscalar type diquark pairs respectively. The numerical results indicate that the scalar mesons $ f_0(980)$ and $a_0(980)$ may have two possible diquark-antidiquark substructures.

Wei-Min Yang

Papers

Analysis the $f_0(980)$ and $a_0(980)$ mesons as four-quark states with the QCD sum rules