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Register a new userSpectrum of low-lying $s^{3}Qbar{Q}$ configurations with negative parity
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Spectrum of low-lying five-quark configurations with strangeness quantum number $S=-3$ and negative parity is studied in three kinds of constituent quark models, namely the one gluon exchange, Goldstone Boson exchange, and instanton-induced hyperfine interaction models, respectively. Our numerical results show that the lowest energy states in all the three employed models are lying at $sim$1800 MeV, about 200 MeV lower than predictions of various quenched three-quark models. In addition, it is very interesting that the state with the lowest energy in one gluon exchange model is with spin 3/2, but 1/2 in the other two models.
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Recent discoveries by Belle and BESIII of charged exotic quarkonium-like resonances provide fresh impetus for study of heavy exotic hadrons. In the limit N_c --> infinity, M_Q --> infinity, the (Qbar Q qbar q) tetraquarks (TQ-s) are expected to be narrow and slightly below or above the (Qbar q) and (Q qbar) two-meson threshold. The isoscalar TQ-s manifest themselves by decay to (Qbar Q) pi pi, and the ~30 MeV heavier charged isotriplet TQ-s by decays into (Qbar Q) pi. The new data strongly suggest that the real world with N_c=3, Q=c,b and q,q = u,d is qualitatively described by the above limit. We discuss the relevant theoretical estimates and suggest new signatures for TQ-s in light of the recent discoveries. We also consider baryon-like states (Q Q qbar qbar), which if found will be direct evidence not just for near-threshold binding of two heavy mesons, but for genuine tetraquarks with novel color networks. We stress the importance of experimental search for doubly-heavy baryons in this context.
We present the spectrum of the lightest pentaquark states of both parities and compare it with the present experimental evidence for these states. We have assumed that the main role for their mass splittings is played by the chromo-magnetic interaction. We have also kept into account the $SU(3)_F$ breaking for their contribution and for the spin orbit term. The resulting pattern is in good agreement with experiment.
We have systematically calculated the mass spectra for S-wave and P-wave fully-charm $cbar{c}cbar{c}$ and fully-bottom $bbar{b}bbar{b}$ tetraquark states in the $mathbf{8}_{[Qbar{Q}]}otimes mathbf{8}_{[Qbar{Q}]}$ color configuration, by using the moment QCD sum rule method. The masses for the fully-charm $cbar ccbar c$ tetraquark states are predicted about $6.3-6.5$ GeV for S-wave channels and $7.0-7.2$ GeV for P-wave channels. These results suggest the possibility that there are some $mathbf{8}_{[cbar{c}]}otimes mathbf{8}_{[cbar{c}]}$ components in LHCbs di-$J/psi$ structures. For the fully-bottom $bbar{b}bbar{b}$ system, their masses are calculated around 18.2 GeV for S-wave tetraquark states while 18.4-18.6 GeV for P-wave ones, which are below the $eta_beta_b$ and $Upsilon(1S)Upsilon(1S)$ two-meson decay thresholds.
The relation between the specific shear viscosity $eta/s$ and the dimensionless jet quenching parameter $hat{q}/T^3$ in perturbative QCD is explored at next-to-leading order in the coupling constant. It is shown that the relation changes little, although both transport coefficients independently are subject to large modifications at the NLO level. This finding confirms that the relationship is robust.
We analyze the validity of a commonly used identification between structures of the virtual photon $gamma^*to Qbar Q$ and vector meson $Vto Qbar Q$ transitions. In the existing studies of $S$-wave vector-meson photoproduction in the literature, such an identification is typically performed in the light-front (LF) frame while the radial component of the meson wave function is rather postulated than computed from the first principles. The massive photon-like $Vto Qbar Q$ vertex, besides the $S$-wave component, also contains an extra $D$-wave admixture in the $Qbar Q$ rest frame. However, the relative weight of these contributions cannot be justified by any reasonable nonrelativistic $Qbar Q$ potential model. In this work, we investigate the relative role of the $D$-wave contribution starting from the photon-like quarkonium $Vto Qbar Q$ transition in both frames: in the $Qbar Q$ rest frame (with subsequent Melosh spin transform to the LF frame) and in the LF frame (without Melosh transform). We show that the photon-like transition imposed in the $Qbar Q$ rest frame leads to significant discrepancies with the experimental data. In the second case we find that the corresponding total $J/psi(1S)$ photoproduction cross sections are very close to those obtained with the $S$-wave only $Vto Qbar Q$ transition, both leading to a good description of the data. However, we find that the $S$-wave only transition leads to a better description of photoproduction data for excited heavy quarkonium states, which represent a more effective tool for study of $D$-wave effects. Consequently, the predictions for production of excited states based on the photon-like structure of $Vto Qbar Q$ transition should be treated with a great care due to a much stronger sensitivity of the $D$-wave contribution to the nodal structure of quarkonium wave functions.
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