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Register a new userDeciphering the recently discovered tetraquark candidates around 6.9 GeV
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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 $Xi_{cc}$ 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 tetraquarks, 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 $bar c bar c$ anti-diquark. We examine these states as the analogs of the states $Psi(4360)$ and $Y(4630)$/$Psi(4660)$ 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 $Xi_{cc}overlineXi_{cc}$. Such a decay would be the analog of the decay of the state $Y(4630)$ into to $Lambda_coverlineLambda_c$. 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.
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We propose an {it{ab initio}} method to explore the nature of the newly discovered particle $X$(6900). We find that there should exist another state near the resonance at around 6.9 $mathrm{GeV}$, and the ratio of production cross sections of $X$(6900) to the undiscovered state is very sensitive to the nature of $X$(6900), whereas is almost independent of the transverse momentum and rapidity. This behavior is unlikely changed by higher order corrections. Therefore, the nature of $X$(6900) can be uncovered by experimental facts in the near future. If there is another state near $X$(6900) with cross section larger than half of that of $X$(6900), $X$(6900) should be a tetraquark state. Otherwise, it should be a molecule-like state.
We present the ground and excited state spectra of $Omega^{0}_{c}$ baryons with spin up to 7/2 from lattice quantum chromodynamics with dynamical quark fields. Based on our lattice results, we predict the quantum numbers of five $Omega^{0}_{c}$ baryons, which have recently been observed by the LHCb Collaboration. Our results strongly indicate that the observed states $Omega_c(3000)^0$ and $Omega_c(3050)^0$ have spin-parity $J^P = 1/2^{-}$, the states $Omega_c(3066)^0$ and $Omega_c(3090)^0$ have $J^P = 3/2^{-}$, whereas $Omega_c(3119)^0$ is possibly a $5/2^{-}$ state.
In recent years, hints for multi-lepton anomalies have been accumulated by the analysis of Large Hadron Collider (LHC) data, pointing towards the existence of beyond the Standard Model (SM) Higgs bosons: a new scalar particle $S$ with a mass $m_S$ in the range between $130,$GeV and $160,$GeV, produced from the decay of a heavier new scalar particle, $H$. Motivated by this observation, we perform a search for the signatures of $S$ within this mass region, which has been studied by CMS and ATLAS as a by-product of the SM Higgs searches in the side-bands of the kinematic regions. Combining the $gammagamma$ and $Zgamma$ channels, with associated leptons, di-jets, bottom quarks and missing energy, we obtain a local (global) significance of 5.1$sigma$ (4.8$sigma$) for a mass of $m_S= 151.5$,GeV and provide the preferred ranges for the corresponding (fiducial) cross sections. This is a strong indication for a scalar resonance $S$ decaying into photons, and, to a lesser extent to $Zgamma$, in association with missing energy, jets or leptons. Hints for the decays into, or production in association with, bottom quarks are statistically less significant. In order to test this hypothesis, we propose a search for $Hrightarrow gammagamma boverline{b},tau^+tau^- boverline{b}$ in asymmetric configurations that has not yet been performed by ATLAS and CMS.
Inspired by the recent observation of $chi_{c0}(3930)$, $X(4685)$ and $X(4630)$ by the LHCb Collaboration and some exotic resonances such as $X(4350)$, $X(4500)$, etc. by several experiment collaborations, the $csbar{c}bar{s}$ tetraquark systems with $IJ^{P}=00^+$, $01^+$ and $02^+$ are systematically investigated in the framework of the quark delocalization color screening model(QDCSM). Two structures, the meson-meson and diquark-antidiquark structures, as well as the channel-coupling of all channels of these two configurations are considered in this work. The numerical results indicate that the molecular bound state $bar{D}_{s}D_{s}$ with $IJ^{P}=00^+$ can be supposed to explain the $chi_{c0}(3930)$. Besides, by using the stabilization method, several resonant states are obtained. There are four $IJ^{P}=00^{+}$ states around the resonance mass 4035 MeV, 4385 MeV, 4524 MeV, and 4632 MeV, respectively; one $IJ^{P}=01^{+}$ state around the resonance mass 4327 MeV; and two $IJ^{P}=02^{+}$ states around the resonance mass 4419 MeV and 4526 MeV, respectively. All of them are compact tetraquarks. Among these states, $X(4350)$, $X(4500)$ and $X(4700)$ can be explained as the compact tetraquark state with $IJ^{P}=00^{+}$, and the $X(4274)$ is possible to be a candidate of the compact tetraquark state with $IJ^{P}=01^{+}$. More experimental tests are expected to check the existence of all these possible resonance states.
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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