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We have investigated the process of $Lambda_bto Lambda Dbar{D}$, by taking into account the contributions from the $s$-wave $Dbar{D}$ interaction within the coupled-channel unitary approach, and the intermediate $psi(3770)$ resonance. In addition to the peak of the $psi(3770)$, an enhancement near the $Dbar{D}$ mass threshold is found in the $Dbar{D}$ invariant mass distributions, which should be the reflection of the $Dbar{D}$ bound state. We would like to encourage our experimental colleagues to measure the $Dbar{D}$ invariant mass distribution of the $Lambda_bto Lambda Dbar{D}$ process, which is crucial to search for the $Dbar{D}$ bound state and to understand the heavy-hadron heavy-hadron interactions.
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It is shown that interference of the amplitudes for the decays $Lambda_b to Lambda D$ and $Lambda_b to Lambda bar{D}^0$ gives rise to CP-violation.
We evaluate the s-wave interaction of pseudoscalar and vector mesons with both charm and beauty to investigate the possible existence of molecular $BD$, $B^*D$, $BD^*$, $B^*D^*$, $Bbar D$, $B^*bar D$, $Bbar D^*$ or $B^* bar D^*$ meson states. The scattering amplitude is obtained implementing unitarity starting from a tree level potential accounting for the dominant vector meson exchange. The diagrams are evaluated using suitable extensions to the heavy flavor sector of the hidden gauge symmetry Lagrangians involving vector and pseudoscalar mesons{, respecting heavy quark spin symmetry}. We obtain bound states at energies above 7 GeV for $BD$ ($J^P=0^+$), $B^*D$ ($1^+$), $BD^*$ ($1^+$) and $B^*D^*$ ($0^+$, $1^+$, $2^+$), all in isospin 0. For $Bbar D$ ($0^+$), $B^*bar D$ ($1^+$), $Bbar D^*$ ($1^+$) and $B^*bar D^*$ ($0^+$, $1^+$, $2^+$) we also find similar bound states in $I=0$, but much less bound, which would correspond to exotic meson states with $bar b$ and $bar c$ quarks, and for the $I=1$ we find a repulsive interaction. We also evaluate the scattering lengths in all cases, which can be tested in current investigations of lattice QCD.
In two recent reactions by Belle producing $Dbar D$ and $Dbar D^*$ meson pairs, peaks above threshold have been measured in the differential cross sections, possibly indicating new resonances in these channels. We want to study such reactions from the point of view that the $D$ meson pairs are produced from already known or predicted resonances below threshold. Our study shows that the peak in the $Dbar D^*$ production is not likely to be caused by the X(3872) resonance, but the peak seen in $Dbar D$ invariant mass can be well described if the $Dbar D$ pair comes from the already predicted scalar X(3700) resonance.
In this article, we assume that there exist the pseudoscalar $Dbar{D}_{s0}^*(2317)$ and $D^*bar{D}_{s1}^*(2460)$ molecular states $Z_{1,2}$ and construct the color singlet-singlet molecule-type interpolating currents to study their masses with the QCD sum rules. In calculations, we consider the contributions of the vacuum condensates up to dimension-10 and use the formula $mu=sqrt{M_{X/Y/Z}^{2}-left(2{mathbb{M}}_{c}right)^{2}}$ to determine the energy scales of the QCD spectral densities. The numerical results, $M_{Z_1}=4.61_{-0.08}^{+0.11},text{GeV}$ and $M_{Z_2}=4.60_{-0.06}^{+0.07},text{GeV}$, which lie above the $Dbar{D}_{s0}^*(2317)$ and $D^*bar{D}_{s1}^*(2460)$ thresholds respectively, indicate that the $Dbar{D}_{s0}^*(2317)$ and $D^*bar{D}_{s1}^*(2460)$ are difficult to form bound state molecular states, the $Z_{1,2}$ are probably resonance states.
We study the $Z_{cs}(3985)$ state recently observed by the BESIII Collaboration in the one-boson-exchange model, assuming that it is a $bar{D}_s^{(*)}D^{(*)}$ molecule, which has the quark content $cbar{c}sbar{q}$ with $q = u$, $d$. It is shown that the one-boson-exchange potential is too weak to generate dynamcally $bar{D}_s D$, $bar{D}^*_s D$, and $bar{D}_sD^*$ states, while for the case of $bar{D}^*_s D^*$, very loosely bound states are likely, with binding energies of the order of several MeV. We conclude that, the observed $Z_{cs}(3985)$ state, if confirmed by further experiments, cannot be a pure hadronic molecular state of $bar{D}_s D^*$ and $bar{D}_s^*D$ and could consist of large components of compact nature.
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