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Register a new userSpectroscopy of light tetraquark states
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We address the question whether the lightest scalar mesons sigma and kappa are tetraquarks, as is strongly supported by many phenomenological studies. We present a search for possible light tetraquark states with J^PC=0^++ and I=0, 1/2, 3/2, 2 on the lattice. The spectrum is determined using the generalized eigenvalue method with a number of tetraquark interpolators at the source and the sink. In all the channels, we unavoidably find lowest scattering states pi(k)pi(-k) or K(k)pi(-k) with back-to-back momentum k=0,2*pi/L,.. . However, we find an additional light state in the I=0 and I=1/2 channels, which may be related to the observed resonances sigma and kappa with a strong tetraquark component. In the exotic repulsive channels I=2 and I=3/2, where no resonance is observed, we find no light state in addition to the scattering states.
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We calculate the mass of tetraquark states of all $qqbar q bar q$ quark configurations in a constituent quark model where the Cornell-like potential and one-gluon exchange spin-spin coupling are employed. The three coupling parameters for the Cornell-like potential and one-gluon exchange spin-spin coupling are proposed mass-dependent in accordance with Lattice QCD data, and all model parameters are predetermined by studying light, charmed and bottom mesons. The theoretical predictions for light tetraquarks are compared with the observed exotic meson states in the light-unflavored meson sector, and tentative assignments are suggested. The work suggests that the $f_0(1500)$ and $f_0(1710)$ might be ground light tetraquark states with $J=0$.
The recent confirmation of the charged charmonium like resonance Z(4430) by the LHCb experiment strongly suggests the existence of QCD multi quarks bound states. Some preliminary results about hypothetical flavored tetraquark mesons are reported. Such states are particularly amenable to Lattice QCD studies as their interpolating operators do not overlap with those of ordinary hidden-charm mesons.
The mass spectra of all-charm tetraquark states with the [cc][$bar{c}bar{c}$] quark configuration are investigated. The coulomb plus linear potential is used in conjunction with the relativistic mass correction term $mathcal{O}(frac{1}{m})$. To determine the fitting parameters for all-charm tetraquarks states [cc][$bar{c}bar{c}$], we first calculate the mass spectra of charmonia [c$bar{c}$] and its decay constants ($f^{2}_{P/V}$). We estimated the masses of the tetraquark states in their ground and radially excited states. For mass spectra of tetraquark states, we also included spin-spin, spin-orbital, and tensor interactions. The mass spectra of charmonia produced in this study are reasonably consistent with experimental and theoretical predictions made by others, whilst the mass spectra of the tetraquark states are consistent with previous theoretical predictions. We propose that the X(6900) state, which has a mass range of 6.2 - 6.9 GeV and was recently detected by LHCb, has the quantum numbers $0^{-+}$, $1^{-+}$, $2^{-+}$ and belongs to the P-wave of the all-cham tetraquark state.
We search for the $J^{PC}=0^{--}$ and $1^{+-}$ light tetraquark states with masses up to 2.46~GeV/$c^2$ in $Upsilon(1S)$ and $Upsilon(2S)$ decays with data samples of $(102pm 2)$ million and $(158pm 4)$ million events, respectively, collected with the Belle detector. No significant signals are observed in any of the studied production modes, and 90% credibility level (C.L.) upper limits on their branching fractions in $Upsilon(1S)$ and $Upsilon(2S)$ decays are obtained. The inclusive branching fractions of the $Upsilon(1S)$ and $Upsilon(2S)$ decays into final states with $f_1(1285)$ are measured to be ${cal B}(Upsilon(1S)to f_1(1285)+anything)=(46pm28({rm stat.})pm13({rm syst.}))times 10^{-4}$ and ${cal B}(Upsilon(2S)to f_1(1285)+anything)=(22pm15({rm stat.})pm6.3({rm syst.}))times 10^{-4}$. The measured $chi_{b2} to J/psi + anything$ branching fraction is measured to be $(1.50pm0.34({rm stat.})pm0.22({rm syst.}))times 10^{-3}$, and 90% C.L. upper limits for the $chi_{b0,b1} to J/psi + anything$ branching fractions are found to be $2.3times 10^{-3}$ and $1.1times 10^{-3}$, respectively. For ${cal B}(chi_{b1} to omega + anything)$, the branching fraction is measured to be $(4.9pm1.3({rm stat.})pm0.6({rm syst.}))times 10^{-2}$. %($<3.68times 10^{-2}$ at 90% C.L.). All results reported here are the first measurements for these modes.
The past seventeen years have witnessed tremendous progress on the experimental and theoretical explorations of the multiquark states. The hidden-charm and hidden-bottom multiquark systems were reviewed extensively in [Phys. Rept. 639 (2016) 1-121]. In this article, we shall update the experimental and theoretical efforts on the hidden heavy flavor multiquark systems in the past three years. Especially the LHCb collaboration not only confirmed the existence of the hidden-charm pentaquarks but also provided strong evidence of the molecular picture. Besides the well-known $XYZ$ and $P_c$ states, we shall discuss more interesting tetraquark and pentaquark systems either with one, two, three or even four heavy quarks. Some very intriguing states include the fully heavy exotic tetraquark states $QQbar Qbar Q$ and doubly heavy tetraquark states $QQbar q bar q$, where $Q$ is a heavy quark. The $QQbar Qbar Q$ states may be produced at LHC while the $QQbar q bar q$ system may be searched for at BelleII and LHCb. Moreover, we shall pay special attention to various theoretical schemes. We shall emphasize the model-independent predictions of various models which are truly/closely related to Quantum Chromodynamics (QCD). There have also accumulated many lattice QCD simulations through multiple channel scattering on the lattice in recent years, which provide deep insights into the underlying structure/dynamics of the $XYZ$ states. In terms of the recent $P_c$ states, the lattice simulations of the charmed baryon and anti-charmed meson scattering are badly needed. We shall also discuss some important states which may be searched for at BESIII, BelleII and LHCb in the coming years.
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