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Register a new userHadronic molecules with a ${bar{D}}$ meson in a medium
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We study the effect of a hot and dense medium on the binding energy of hadronic molecules with open-charm mesons. We focus on a recent chiral quark-model-based prediction of a molecular state in the $N bar D$ system. We analyze how the two-body thresholds and the hadron-hadron interactions are modified when quark and meson masses and quark-meson couplings change in a function of the temperature and baryon density according to predictions of the Nambu--Jona-Lasinio model. We find that in some cases the molecular binding is enhanced in medium as compared to their free-space binding. We discuss the consequences of our findings for the search for exotic hadrons in high-energy heavy-ion collisions as well as in the forthcoming facilities FAIR or J-PARC.
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Properties of $rho$-meson in symmetric nuclear matter are investigated in a light-front constituent quark model (LFCQM), using the in-medium inputs calculated by the quark-meson coupling (QMC) model. The LFCQM used in this study was already applied for the studies of the electromagnetic properties of $rho$-meson in vacuum, namely, the charge~$G_0$, magnetic~$G_1$, and quadrupole~$G_2$ form factors, electromagnetic charge radius, and electromagnetic decay constant. We predict that the electromagnetic decay constant, charge radius, and quadrupole moment are enhanced as increasing the nuclear matter density, while the magnetic moment is slightly quenched. Furthermore, we predict that the value $Q^2_{rm zero}$, which crosses zero of the charge form factor, $G_0(Q^2_{rm zero})=0$ ($Q^2 = -q^2 > 0$ with $q$ being the four-momentum transfer), decreases as increasing the nuclear matter density.
We propose to describe the heavy and exotic tetraquark state as a holographic molecule by binding the lightest heavy-light meson $(0^-, 1^-)$ multiplet to a flavored sphaleron in the bulk of the Witten-Sakai-Sugimoto model. The strongly bound tetraquark state emerges as an Efimov state with a binding energy that is comparable to that reported in recent lattice simulations and standard quark model estimates for bottom. Our construction finds charm and mixed charm-bottom tetraquark states to be also bound. The unique feature of these states stems from the fact that they are perhaps the first manifestation of the Efimov bound state mechanism in the hadronic world.
Starting from a molecular picture for the X(3872) resonance, this state and its J^{PC}=2++ HQSS partner [X2(4012)] are analyzed within a model which incorporates possible mixings with 2P charmonium states. Since it is reasonable to expect the bare chi_{c1}(2P) to be located above the Dbar D* threshold, but relatively close to it, the presence of the charmonium state provides an effective attraction that will contribute to bind the X(3872), but it will not appear in the 2++ sector. Indeed in this latter sector, the chi_{c2}(2P) should provide an effective small repulsion, because it is placed well below the D*bar D* threshold. We show how the 1++ and 2++ bare charmonium poles are modified due to the D(*)bar D(*) loop effects, and the first one is moved to the complex plane. The meson loops produce, besides some shifts in the masses of the charmonia, a finite width for the 1++ dressed charmonium state. On the other hand, the X(3872) and X2(4012) start developing some charmonium content, which is estimated by means of the compositeness Weinberg sum-rule. We also show that for X(3872) molecular probabilities of around 70-90 %, the X2 resonance destabilizes and disappears from the spectrum, becoming either a virtual state or being located deep into the complex plane, with decreasing influence in the D* bar D* scattering line.
With quark-antiquark annihilation and creation in the first Born approximation, we study the reactions: $K bar {K} to K bar {K}^ast, ~K bar{K} to K^* bar{K}, ~pi K to pi K^ast, ~pi K to rho K, ~pi pi to K bar{K}^ast, ~pi pi to K^ast bar{K}, ~pi pi to K^ast bar{K}^ast, ~pi rho to K bar{K}, ~pi rho to K^ast bar{K}^ast, ~rho rho to K^ast bar{K}^ast, ~K bar{K}^ast to rho rho$, and $K^* bar{K} to rho rho$. Unpolarized cross sections for the reactions are obtained from transition amplitudes that are composed of mesonic quark-antiquark relative-motion wave functions and the transition potential for quark-antiquark annihilation and creation. From a quark-antiquark potential that is equivalent to the transition potential, we prove that the total spin of the two final mesons may not equal the total spin of the two initial mesons. Based on flavor matrix elements, cross sections for some isospin channels of reactions can be obtained from the other isospin channels of reactions. Remarkable temperature dependence of the cross sections is found.
With the PICR hydrodynamic model, we study the polarization splitting between $Lambda$ and $bar{Lambda}$ at RHIC BES energy range, based on the meson field mechanism. Our results fit to the experimental data fairly well. Besides, two unexpected effect emerges: (1) the baryon density gradient has non-trivial and negative contribution to the polarization splitting; (2) for 7.7 GeV Au+Au collisions within the centrality range of 20%-50%, the polarization splitting surprisingly increases with the centrality decreases. The second effect might help to explain the significant signal of polarization splitting measured in STARs Au+Au 7.7 Gev collisions.
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