We study two- and three-baryon systems with two units of charm looking for possible bound states or resonances. All two-baryon interactions are consistently derived from a constituent quark model tuned in the light-flavor hadron phenomenology: spectr
a and interactions. The presence of the heavy quarks makes the two-body interactions simpler than in the light-flavor sector. Our results show a narrow two-body resonance with quantum numbers $(I,J^P)=(0,0^+)$. It is located 6.2 MeV below the $Sigma_cSigma_c$ threshold and has a width of 4.7 MeV. The foregoing two-body state contributes to generate a $N Sigma_cSigma_c$ resonance with quantum numbers $(I,J^P)=(1/2,1/2^+)$ and a separation energy of 0.2 MeV.
We discuss the stability of hidden and open heavy-flavor hadronic states made of either two or three mesons. References are made in passing to studies regarding two and three-body systems containing baryons. We perform a comparative study analyzing t
he results in terms of quark and hadron degrees of freedom. Compact and molecular states are found to exist in very specific situations. We estimate the decay width for the different scenarios: weak decays for bound states by the strong interaction, and strong decays for hadronic resonances above a decay threshold. The experimental observation of narrow hadrons lying well above their lowest decay threshold is theoretically justified.
We use an existing model of the $LambdaLambda N - Xi NN$ three-body system based in two-body separable interactions to study the $(I,J^P)=(1/2,1/2^+)$ three-body channel. For the $LambdaLambda$, $Xi N$, and $LambdaLambda - Xi N$ amplitudes we have co
nstructed separable potentials based on the most recent results of the HAL QCD Collaboration. They are characterized by the existence of a resonance just below or above the $Xi N$ threshold in the so-called $H$-dibaryon channel, $(i,j^p)=(0,0^+)$. A three-body resonance appears {2.3} MeV above the $Xi d$ threshold. We show that if the $LambdaLambda - Xi N$ $H$-dibaryon channel is not considered, the $LambdaLambda N - Xi NN$ $S$ wave resonance disappears. Thus, the possible existence of a $LambdaLambda N - Xi NN$ resonance would be sensitive to the $LambdaLambda - Xi N$ interaction. The existence or nonexistence of this resonance could be evidenced by measuring, for example, the $Xi d$ cross section.
We review the status as regards the existence of three- and four-body bound states made of neutrons and $Lambda$ hyperons. For interesting cases, the coupling to neutral baryonic systems made of charged particles of different strangeness has been add
ressed. There are strong arguments showing that the $Lambda nn$ system has no bound states. $LambdaLambda nn$ strong stable states are not favored by our current knowledge of the strangeness $-1$ and $-2$ baryon-baryon interactions. However, a possible $Xi^- t$ quasibound state decaying to $LambdaLambda nn$ might exist in nature. Similarly, there is a broad agreement about the nonexistence of $LambdaLambda n$ bound states. However, the coupling to $Xi NN$ states opens the door to a resonance above the $LambdaLambda n$ threshold.
We briefly review the stability of the $QQbar qbar q$-type of tetraquarks with two heavy quarks and two light antiquarks. We present the first comprehensive estimate of the lifetime and leading decay modes of the exotic meson $bbbar ubar d$ with double beauty.
We study the coupled $LambdaLambda nn-Xi^- pnn$ system to check whether the inclusion of channel coupling is able to bind the $LambdaLambda nn$ system. We use a separable potential three-body model of the coupled $LambdaLambda nn - Xi^- pnn$ system a
s well as a variational four-body calculation with realistic interactions. Our results exclude the possibility of a $LambdaLambda nn$ bound state by a large margin. However, we have found a $Xi^- t$ quasibound state above the $LambdaLambda nn$ threshold.
We present the first full-fledged study of the flavor-exotic isoscalar $T_{bb}^-equiv b b bar u bar d$ tetraquark with spin and parity $J^P=1^+$. We report accurate solutions of the four-body problem in a quark model, characterizing the structure of
the state as a function of the ratio $M_Q/m_q$ of the heavy to light quark masses. For such a standard constituent model, $T_{bb}^-$ lies approximately 150 MeV below the strong decay threshold $B^-bar {B^*}^{0}$ and 105 MeV below the electromagnetic decay threshold $B^- bar B^0 gamma$. We evaluate the lifetime of $T_{bb}^-$, identifying the promising decay modes where the tetraquark might be looked for in future experiments. Its total decay width is $Gamma approx 87 times 10^{-15}$ GeV and therefore its lifetime $tau approx$ 7.6 ps. The promising final states are ${B^*}^{-}, {D^*}^{+} , ell^- , bar u_ell$ and $bar {B^*}^{0} , {D^*}^{0} , ell^- , bar u_ell $ among the semileptonic decays, and ${B^*}^{-} , {D^*}^{+} , {D_s^*}^-$, $bar {B^*}^{0} , {D^*}^{0} , {D_s^*}^- $, and ${B^*}^{-} , {D^*}^{+} , rho^-$ among the nonleptonic ones. The semileptonic decay to the isoscalar $J^P=0^+$ tetraquark $T_{bc}^0$ is also relevant but it is not found to be dominant. There is a broad consensus about the existence of this tetraquark, and its detection will validate our understanding of the low-energy realizations of Quantum Chromodynamics (QCD) in the multiquark sector.
We present a comparative study of the charmed baryon$-$nucleon interaction based on different theoretical approaches. For this purpose, we make use of i) a constituent quark model tuned in the light-flavor baryon$-$baryon interaction and the hadron s
pectra, ii) existing results in the literature based both on hadronic and quark-level descriptions, iii) (2+1)-flavor lattice QCD results of the HAL QCD Collaboration at unphysical pion masses and their effective field theory extrapolation to the physical pion mass. There is a general qualitative agreement among the different available approaches to the charmed baryon$-$nucleon interaction. Different from hadronic models based on one-boson exchange potentials, quark$-$model based results point to soft interactions without two-body bound states. They also support a negligible channel coupling, due either to tensor forces or to transitions between different physical channels, $Lambda_c N - Sigma_c N$. Short-range gluon and quark-exchange dynamics generate a slightly larger repulsion in the $^1S_0$ than in the $^3S_1$ $Lambda_c N$ partial wave. A similar asymmetry between the attraction in the two $S$ waves of the $Lambda_c N$ interaction also appears in hadronic approaches. A comparative detailed study of Pauli suppressed partial waves, as the $^1S_0 (I=1/2)$ and $^3S_1 (I=3/2)$ $Sigma_c N$ channels, would help to disentangle the short-range dynamics of two-baryon systems containing heavy flavors. The possible existence of charmed hypernuclei is discussed.
We investigate the production of exotic tetraquarks, $QQbar{q}bar{q} equiv T_{QQ}$ ($Q=c$ or $b$ and $q=u$ or $d$), in relativistic heavy-ion collisions using the quark coalescence model. The $T_{QQ}$ yield is given by the overlap of the density matr
ix of the constituents in the emission source with the Wigner function of the produced tetraquark. The tetraquark wave function is obtained from exact solutions of the four-body problem using realistic constituent models. The production yields are typically one order of magnitude smaller than previous estimations based on simplified wave functions for the tetraquarks. We also evaluate the consequences of the partial restoration of chiral symmetry at the hadronization temperature on the coalescence probability. Such effects, in addition to increasing the stability of the tetraquarks, lead to an enhancement of the production yields, pointing towards an excellent discovery potential in forthcoming experiments. We discuss further consequences of our findings for the search of exotic tetraquarks in central Pb+Pb collisions at the LHC.
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 i
s not favorable, and, as a consequence, no bound state is found below the lowest dissociation threshold.
