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Register a new userHeavy quark spin symmetric molecular states from ${bar D}^{(*)}Sigma_c^{(*)}$ and other coupled channels in the light of the recent LHCb pentaquarks
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We consider the ${bar D}^{(*)}Sigma_c^{(*)}$ states, together with $J/psi N$ and other coupled channels, and take an interaction consistent with heavy quark spin symmetry, with the dynamical input obtained from an extension of the local hidden gauge approach. By fitting only one parameter to the recent three pentaquark states reported by the LHCb collaboration, we can reproduce the three of them in base to the mass and the width, providing for them the quantum numbers and approximate molecular structure as $1/2^-$ $bar{D} Sigma_c$, $1/2^-$ $bar{D}^* Sigma_c$, and $3/2^-$ $bar{D}^* Sigma_c$, and isospin $I=1/2$. We find another state around 4374 MeV, of $3/2^-$ $bar{D} Sigma_c^*$ structure, for which indications appear in the experimental spectrum. Two other near degenerate states of $1/2^-$ $bar{D}^* Sigma_c^*$ and $3/2^-$ $bar{D}^* Sigma_c^*$ nature are also found around 4520 MeV, which although less clear, are not incompatible with the observed spectrum. In addition, a $5/2^-$ $bar D^* Sigma_c^*$ state at the same energy appears, which however does not couple to $J/psi p$ in $S-$wave, and hence it is not expected to show up in the LHCb experiment.
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The effects of the $Sigma_cbar{D}^*$-$Lambda_{c}(2595)bar{D}$ coupled-channel dynamics and various one-boson-exchange (OBE) forces for the LHCb pentaquark states, $P_c(4440)$ and $P_c(4457)$, are reinvestigated. Both the pion and $rho$-meson exchanges are considered for the $Sigma_cbar{D}^*$-$Lambda_{c}(2595)bar{D}$ coupled-channel dynamics. It is found that the role of the $Lambda_{c}(2595)bar{D}$ channel in the descriptions of the $P_c(4440)$ and $P_c(4457)$ states is not significant with the OBE parameters constrained by other experimental sources. The naive OBE models with the short-distance $delta(vec{r})$ term of the one-pion exchange (OPE) kept fail to reproduce the $P_c(4440)$ and $P_c(4457)$ states simultaneously. The OPE potential with the full $delta(vec{r})$ term results in a too large mass splitting for the $J^P=1/2^-$ and $3/2^-$ $Sigma_cbar{D}^*$ bound states with total isospin $I=1/2$. The OBE model with only the OPE $delta(vec{r})$ term dropped may fit the splitting much better, but somewhat underestimates the splitting. Since the $delta(vec r)$ potential is from short-distance physics, which also contains contributions from the exchange of mesons heavier than those considered explicitly, we vary the strength of the $delta(vec r)$ potential and find that the masses of the $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$ can be reproduced simultaneously with the $delta(vec r)$ term in the OBE model reduced by about 80%. While two different spin assignments are possible to produce their masses, in the preferred description the spin-parities of the $P_c(4440)$ and $P_c(4457)$ are $3/2^-$ and $1/2^-$, respectively.
On March 26th, 2019, at the Rencontres de Moriond QCD conference, the LHCb Collaboration reported the observation of three new pentaquarks, namely $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$, which are consistent with the loosely bound molecular hidden-charm pentaquark states composed of an S-wave charmed baryon $Sigma_c$ and an S-wave anti-charmed meson ($bar{D}, bar{D}^*$). In this work, we present a direct calculation by the one-boson-exchange (OBE) model and demonstrate explicitly that the $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ do correspond to the loosely bound $Sigma_cbar{D}$ with $(I=1/2,J^P=1/2^-)$, $Sigma_cbar{D}^*$ with $(I=1/2,J^P=1/2^-)$ and $Sigma_cbar{D}^*$ with $(I=1/2,J^P=3/2^-)$, respectively.
The two exotic $P_c^+(4380)$ and $P_c^+(4450)$ discovered in $2015$ by the LHCb Collaboration, together with the four resonances $X(4140)$, $X(4274)$, $X(4500)$ and $X(4700)$, reported in $2016$ by the same collaboration, are described in a constituent quark model which has been able to explain the properties of charmonium states from the $J/psi$ to the $X(3872)$. Using this model we found a $bar DSigma_c^*$ bound state with $J^P=frac{3}{2}^-$ that may be identified with the $P_c^+(4380)$. In the $bar D^*Sigma_c$ channel we found three possible candidates for the $P_c^+(4450)$ with $J^P=frac{1}{2}^-$, $frac{3}{2}^-$ and $frac{3}{2}^+$ with almost degenerated energies. The $X(4140)$ resonance appears as a cusp in the $J/psiphi$ channel due to the near coincidence of the $D_{s}^{pm}D_{s}^{astpm}$ and $J/psiphi$ mass thresholds. The remaining three $X(4274)$, $X(4500)$ and $X(4700)$ resonances appear as conventional charmonium states with quantum numbers $3^{3}P_{1}$, $4^{3}P_{0}$ and $5^{3}P_{0}$, respectively; and whose masses and widths are slightly modified due to their coupling with the corresponding closest meson-meson thresholds.
The recently discovered $P_c(4380)^+$ and $P_c(4450)^+$ states at LHCb have masses close to the $bar DSigma_c^*$ and $bar D^*Sigma_c$ thresholds, respectively, which suggest that they may have significant meson-baryon molecular components. We analyze these states in the framework of a constituent quark model which has been applied to a wide range of hadronic observables, being the model parameters, therefore, completely constrained. The $P_c(4380)^+$ and $P_c(4450)^+$ are studied as molecular states composed by charmed baryons and open charm mesons. Several bound states with the proper binding energy are found in the $bar DSigma_c^*$ and $bar D^*Sigma_c$ channels. We discuss the possible assignments of these states from their decay widths. Moreover, two more states are predicted, associated with the $bar DSigma_c$ and $bar D^* Sigma_c^*$ thresholds.
In this work, we preform a systematic investigation about hidden heavy and doubly heavy molecular states from the $D^{(*)}bar{D}^{(*)}/B^{(*)}bar{B}^{(*)}$ and $D^{(*)}D^{(*)}/bar{B}^{(*)}bar{B}^{(*)}$ interactions in the quasipotential Bethe-Salpeter equation (qBSE) approach. With the help of the Lagrangians with heavy quark and chiral symmetries, interaction potentials are constructed within the one-boson-exchange model in which we include the $pi$, $eta$, $rho$, $omega$ and $sigma$ exchanges, as well as $J/psi$ or $Upsilon$ exchange. Possible bound states from the interactions considered are searched for as the pole of scattering amplitude. The results suggest that experimentally observed states, $Z_c(3900)$, $Z_c(4020)$, $Z_b(10610)$, and $Z_b(10650)$, can be related to the $Dbar{D}^{*}$, $D^*bar{D}^{*}$, $Bbar{B}^{*}$, and $B^*bar{B}^{*}$ interactions with quantum numbers $I^G(J^P)=1^+(1^{+})$, respectively. The $Dbar{D}^{*}$ interaction is also attractive enough to produce a pole with $0^+(0^+)$ which is related to the $X(3872)$. Within the same theoretical frame, the existence of $Dbar{D}$ and $Bbar{B}$ molecular states with $0(0^+)$ are predicted. The possible $D^*bar{D}^*$ molecular states with $0(0^+, 1^+, 2^+)$ and $1(0^+)$ and their bottom partners are also suggested by the calculation. In the doubly heavy sector, no bound state is produced from the $DD/bar{B}bar{B}$ interaction while a bound state is found with $0(1^+)$ from $DD^*/bar{B}bar{B}^*$ interaction. The $D^*D^*/bar{B}^*bar{B}^*$ interaction produces three molecular states with $0(1^+)$, $0(2^+)$ and $1(2^+)$.
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