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Register a new userIs the $Y(2175)$ a Strangeonium Hybrid Meson?
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QCD Gaussian sum-rules are used to explore the vector ($J^{PC}=1^{--}$) strangeonium hybrid interpretation of the $Y(2175)$. Using a two-resonance model consisting of the $Y(2175)$ and an additional resonance, we find that the relative resonance strength of the $Y(2175)$ in the Gaussian sum-rules is less than 5% that of a heavier 2.9 GeV state. This small relative strength presents a challenge to a dominantly-hybrid interpretation of the $Y(2175)$.
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We suggest that the recently discovered charm-strange meson D_sJ(2632), with unusual properties, could be a cyptoexotic tetraquark baryonium state cdd_bars_bar. We predict other four narrow states, as Regge recurrences of D_sJ(2632), below the possible baryon-antibaryon thresholds.
We report on some ideas concerning the nature of the X(3872) resonance and the need for approximately equal charged and neutral components of $D bar{D}^* +cc$. Then we discuss how some hidden charm states are obtained from the interaction between vector mesons with charm and can be associated to some of the charmonium-like X,Y,Z states. Finally we discuss how the nature of these states could be investigated through different types of radiative decay.
The strangeonium-like $sbar{s}g$ hybrids are investigated from lattice QCD in the quenched approximation. In the Coulomb gauge, spatially extended operators are constructed for $1^{--}$ and $(0,1,2)^{-+}$ states with the color octet $sbar{s}$ component being separated from the chromomagnetic field strength by spatial distances $r$, whose matrix elements between the vacuum and the corresponding states are interpreted as Bethe-Salpeter (BS) wave functions. In each of the $(1,2)^{-+}$ channels, the masses and the BS wave functions are reliably derived. The $1^{-+}$ ground state mass is around 2.1-2.2 GeV, and that of $2^{-+}$ is around 2.3-2.4 GeV, while the masses of the first excited states are roughly 1.4 GeV higher. This mass splitting is much larger than the expectation of the phenomenological flux-tube model or constituent gluon model for hybrids, which is usually a few hundred MeV. The BS wave functions with respect to $r$ show clear radial nodal structures of non-relativistic two-body system, which imply that $r$ is a meaningful dynamical variable for these hybrids and motivate a color halo picture of hybrids that the color octet $sbar{s}$ is surrounded by gluonic degrees of freedom. In the $1^{--}$ channel, the properties of the lowest two states comply with those of $phi(1020)$ and $phi(1680)$. We have not obtained convincing information relevant to $phi(2170)$ yet, however, we argue that whether $phi(2170)$ is a conventional $sbar{s}$ meson or a $sbar{s}g$ hybrid within the color halo scenario, the ratio of partial decay widths $Gamma(phi eta)$ and $Gamma (phi eta)$ observed by BESIII can be understood by the mechanism of hadronic transition of a strangeonium-like meson along with the $eta-eta$ mixing.
We calculate the complete form of the dimension-8 condensate contributions in the two-point correlator of the ($1^{-+}$,$0^{++}$) light hybrid current considering the operator mixing under renormalization. We find the inclusion these higher power corrections as well as the update of $langle g^3G^3rangle$ increase the QCD sum rule mass prediction for the $1^{-+}$ light hybrid. The obtained conservative mass range 1.72--2.60 GeV does not favor the $pi_1(1400)$ and the $pi_1(1600)$ to be pure hybrid states and suggests the $pi_1(2015)$ observed by E852 is more likely to have much of a hybrid constituent. We also study the $b_1pi$ and $rhopi$ decay patterns of the $1^{-+}$ light hybrid with light-cone QCD sum rules. We obtain a relatively large partial decay width of the $b_1pi$ mode, which is consistent with the predictions from the flux tube models and lattice QCD. More interestingly, using the tensor interpolating current we find the partial decay width of the $rhopi$ mode is small due to the absence of the leading twist contribution in the light-cone expansion of the correlation function.
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 $D^*to gamma/pi+D$ decays. The decay of the vector $Y$ into a pion and a $Z_c$ state requires a flip of charge conjugation and isospin that is described appropriately in the formalism used. Rates however are found to depend on the fifth power of pion momentum which would make the final states $pi Z_c(4020)$ strongly suppressed with respect to $pi Z_c(3900)$. The agreement with BES III data would be improved considering the $pi Z_c(4020)$ 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.
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