arXiv subjects
Publications and source records attributed to A. Valcarce.
We use a constituent model to analyze the stability of pentaquark $\bar Q qqqq$ configurations with a heavy antiquark $\bar c$ or $\bar b$, and four light quarks $uuds$, $ddsu$ or $ssud$. The interplay between chromoelectric and chromomagnetic effects is not favorable, and, as a consequence, no bound state is found below the lowest dissociation threshold.
We outline the most important results regarding the stability of doubly heavy tetraquarks $QQ\bar q\bar q$ with an adequate treatment of the four-body dynamics. We consider both color-mixing and spin-dependent effects. Our results are straightforwardly applied to the case of all-heavy tetraquarks $QQ\bar Q\bar Q$. We conclude that the stability is favored in the limit $M_Q/m_q \gg 1$ pointing to the stability of the $bb\bar u\bar d$ state and the instability of all-heavy tetraquarks.
We study the temperature and baryon density dependence of the masses of the lightest charmed baryons $Λ_c$, $Σ_c$ and $Σ^*_c$. We also look at the effects of the temperature and baryon density on the binding energies of the $Λ_c N$ and $Λ_c Λ_c$ systems. Baryon masses and baryon-baryon interactions are evaluated within a chiral constituent quark model. Medium effects are incorporated in those parameters of the model related to the dynamical breaking of chiral symmetry, which are the masses of the constituent quarks, the $σ$ and $π$ meson masses, and quark-meson couplings. We find that while the in-medium $Λ_c$ mass decreases monotonically with temperature, those of $Σ_c$ and $Σ^*_c$ have a nonmonotonic dependence. These features can be understood in terms of a simple group theory analysis regarding the one-gluon exchange interaction in those hadrons. The in-medium $Λ_c N$ and $Λ_c Λ_c$ interactions are governed by a delicate balance involving a stronger attraction due to the decrease of the $σ$ meson mass, suppression of coupled-channel effects and lower thresholds, leading to shallow bound states with binding energies of a few~MeV. The $Λ_c$ baryon could possibly be bound to a large nucleus, in qualitative agreement with results based on relativistic mean field models or QCD sum rules. Ongoing experiments at RHIC or LHCb or the planned ones at FAIR and J-PARC may take advantage of the present results.
The lattice QCD analyses of the HAL QCD Collaboration predicts a strongly attractive potential in the $ΩN$ $^5S_2$ channel which supports a bound state. In this paper we show that this $ΩN$ channel together with the $NN$ $^3S_1$ channel give rise to a $Ωd$ bound state in the state with maximal spin $(I,J^P)=(0,5/2^+)$ with a binding energy of $\sim$ 17 MeV.
By solving exactly the Faddeev equations for the bound-state problem of three mesons, we demonstrate that current theoretical predictions pointing to the existence of a deeply-bound doubly bottom axial vector tetraquark lead to the existence of a unique bound state of three $B$ mesons. We find that the $BB^*B^*-B^*B^*B^*$ state with quantum numbers $(I)J^P=(1/2)2^-$, $T_{bbb}$, is about 90\,MeV below any possible three $B$-meson threshold for the reported binding of the doubly bottom axial vector tetraquark, $T_{bb}$.
It has been recently reported an intriguing theoretical result of a narrow three-body resonance with a large available phase space. The resonance was reported in the $NΛΛ-ΞNN$ system near the $Ξd$ threshold, having a very small width in spite of the open $NΛΛ$ channel lying around 23 MeV below the $ΞNN$ channel. We use first-order perturbation theory as a plausible argument to explain this behavior. We apply our result to realistic local interactions. Other systems involving several thresholds are likely to follow the same behavior.
We study the width of a two-body resonance in a coupled-channel system. We demonstrate how the width does not come only determined by the available phase space for its decay to the detection channel, but it greatly depends on the relative position of the mass of the resonance with respect to the masses of the coupled-channels generating the state. Our results are consistent with the experimental observation of narrow hadrons lying well above their lowest decay threshold.
It is shown that standard constituent quark models produce $(\bar c c qqq)$ hidden-charm pentaquarks, where $c$ denotes the charmed quark and $q$ a light quark, which lie below the lowest threshold for spontaneous dissociation and thus are stable in the limit where the internal $\bar c c$ annihilation is neglected. The binding is a cooperative effect of the chromoelectric and chromomagnetic components of the interaction, and it disappears in the static limit with a pure chromoelectric potential. Their wave function contains color sextet and color octet configurations for the subsystems and can hardly be reduced to a molecular state made of two interacting hadrons. These pentaquark states could be searched for in the experiments having discovered or confirmed the hidden-charm meson and baryon resonances.
Using local central Yukawa-type Malfliet-Tjon interactions reproducing the low-energy parameters and phase shifs of the $nn$ system and the latest updates of the $nΛ$ and $ΛΛ$ Nijmegen ESC08c potentials we study the possible existence of a ${}_{ΛΛ}^{\,\,\,\,4}n$ bound state. Our results indicate that the ${}_{ΛΛ}^{\,\,\,\,4}n$ is unbound, being just above threshold. We discuss the role played by the $^1S_0$ $nn$ repulsive term of the Yukawa-type Malfliet-Tjon interaction.
This Workshop brought top experts, researchers, postdocs, and students from high-energy heavy ion interactions, lattice QCD and hadronic physics communities together. YSTAR2016 discussed the impact of "missing" hyperon resonances on QCD thermodynamics, on freeze-out in heavy ion collisions, on the evolution of early universe, and on the spectroscopy of strange particles. Recent studies that compared lattice QCD predictions of thermodynamic properties of quark-gluon plasma at freeze-out with calculations based on statistical hadron resonance gas models as well as experimentally measured ratios between yields of different hadron species in heavy ion collisions provide indirect evidence for the presence of "missing" resonances in all of these contexts. The aim of the YSTAR2016 Workshop was to sharpen these comparisons and advance our understanding of the formation of strange hadrons from quarks and gluons microseconds after the Big Bang and in todays experiments at LHC and RHIC as well as at future facilities like FAIR, J-PARC and KL at JLab. It was concluded that the new initiative to create a secondary beam of neutral kaons at JLab will make a bridge between the hardron spectroscopy, heavy-ion experiments and lattice QCD studies addressing some major issues related to thermodynamics of the early universe and cosmology in general.
This paper provides results for the ground state and excited spectra of three-flavored doubly heavy baryons, $bcn$ and $bcs$. We take advantage of the spin-independent interaction recently obtained to reconcile the lattice SU(3) QCD static potential and the results of nonperturbative lattice QCD for the triply heavy baryon spectra. We show that the spin-dependent potential might be constrained on the basis of nonperturbative lattice QCD results for the spin splittings of three-flavored doubly heavy baryons. Our results may also represent a challenge for future lattice QCD work, because a smaller lattice error could help in distinguishing between different prescriptions for the spin-dependent part of the interaction. Thus, by comparing with the reported baryon spectra obtained with parameters estimated from lattice QCD, one can challenge the precision of lattice calculations. The present work supports a coherent description of singly, doubly and triply heavy baryons with the same Cornell-like interacting potential. The possible experimental measurement of these states at LHCb is an incentive for this study.
By using local central Yukawa-type interactions that reproduce the low-energy parameters of the latest updates of the Nijmegen ESC08c potentials we show that the $NΞ$, $NNΞ$, $NΞΞ$ and $NNΞΞ$ systems with maximal isospin are bound. Since in these states the strong decay $NΞ\toΛΛ$ is forbidden by isospin conservation, these strange few-body systems will be stable under the strong interaction. These results may suggest that other states with different number of $N$'s and $Ξ$'s in the maximal isospin channel could also be bound.
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.
We study the stability of hexaquark systems containing two heavy quarks and four light quarks within a simple quark model. No bound or metastable state is found. The reason stems on a delicate interplay between chromoelectric and chromomagnetic effects. Our calculation provides also information about anticharmed pentaquarks that are seemingly unbound in simple quark models.
The recent update of the strangeness $-2$ ESC08c Nijmegen potential incorporating the NAGARA and KISO events predicts a $ΞN$ bound state, $D^*$, in the $^3S_1 (I=1)$ channel. We study if the existence of this two-body bound state could give rise to stable three-body systems. For this purpose we solve the bound state problem of three-body systems where the $ΞN$ state is merged with $N$'s, $Λ$'s, $Σ's$ or $Ξ$'s, making use of the most recent updates of the two-body ESC08c Nijmegen potentials. We found that there appear stable states in the $ΞNN$ and $ΞΞN$ systems, the $ΞΛN$ and $ΞΣN$ systems being unbound.
We present a neat example of a meson--baryon system where the vicinity of two different thresholds enhances the binding of a hadronic resonance, a pentaquark. As a consequence the pattern of states may change when moving among different flavor sectors, what poses a warning on naive extrapolations to heavy flavor sectors based on systematic expansions. For this purpose we simultaneously analyze the $N\bar D$ and $NB$ two-hadron systems looking for possible bound states or resonances. When a resonance is controlled by a coupled-channel effect, going to a different flavor sector may enhance or diminish the binding. This effect may, for example, generate significant differences between the charmonium and bottomonium spectra above open-flavor thresholds or pentaquark states in the open-charm and open-bottom sectors.
In this talk we present a mechanism giving rise to exotic $XYZ$ four-quark states in the meson spectra within a constituent quark model approach. We discuss its generalization to five-quark states in the heavy baryon sector. Finally, we revise some other works in the literature and experimental data where this mechanism may be working.
We have used realistic local interactions based on the recent update of the strangeness $-2$ Nijmegen ESC08c potential to calculate the bound state problem of the $ΞNN$ system in the $(I)J^P=(\frac{1}{2})\frac{3}{2}^+$ state. We found that this system presents a deeply bound state lying $13.5$ MeV below the $Ξd$ threshold. Since in lowest order, pure S$-$wave configuration, this system can not decay into the open $ΛΛN$ channel, its decay width is expected to be very small. We have also recalculated the $(I)J^P=(\frac{3}{2})\frac{1}{2}^+$ state and we have compared with results of quark-model based potentials.