The past decades witnessed the golden era of hadron physics. Many excited open heavy flavor mesons and baryons have been observed since 2017. We shall provide an updated review of the recent experimental and theoretical progresses in this active field. Besides the conventional heavy hadrons, we shall also review the recently observed open heavy flavor tetraquark states X(2900) and Tcc+(3875) as well as the hidden heavy flavor multiquark states X(6900), Pcs(4459)0 , Zcs(3985)− , Zcs(4000)+ , and Zcs(4220)+ . We will also cover the recent progresses on the glueballs and light hybrid mesons, which are the direct manifestations of the non-Abelian SU(3) gauge interaction of the Quantum Chromodynamics in the low-energy region.

/pdf/an-updated-review-of-the-new-hadron-states-2by2tnvk.pdf

An updated review of the new hadron states

The observation of the $P_{cs}(4459)$ by the LHCb collaboration adds a new member to the set of known hidden-charm pentaquarks, which includes the $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$. The $P_{cs}(4459)$ is expected to have the light-quark content of a $\Lambda$ baryon ($I=0$, $S=-1$), but its spin is unknown. Its closeness to the $\bar{D}^* \Xi_c$ threshold -- $4478\,{\rm MeV}$ in the isospin-symmetric limit -- suggests the molecular hypothesis as a plausible explanation for the $P_{cs}(4459)$. While in the absence of coupled-channel dynamics heavy-quark spin symmetry predicts the two spin-states of the $\bar{D}^* \Xi_c$ to be degenerate, power counting arguments indicate that the coupling with the nearby $\bar{D} \Xi_c'$ and $\bar{D} \Xi_c^*$ channels might be a leading order effect. This generates a hyperfine splitting in which the $J=\tfrac{3}{2}$ $\bar{D}^* \Xi_c$ pentaquark will be lighter than the $J=\tfrac{1}{2}$ configuration, which we estimate to be of the order of $5-15\,{\rm MeV}$. We also point out an accidental symmetry between the $P_{cs}(4459)$ and $P_c(4440/4457)$ potentials. Finally, we argue that the spectroscopy and the $J/\psi \Lambda$ decays of the $P_{cs}(4459)$ might suggest a marginal preference for $J = \tfrac{3}{2}$ over $J = \tfrac{1}{2}$.

/pdf/the-p-cs-4459-pentaquark-from-a-combined-effective-field-4u6agkw3wo.pdf

The $P_{cs}(4459)$ pentaquark from a combined effective field theory and phenomenological perspectives

The observation of the $$P_{cs}(4459)$$
 by the LHCb collaboration adds a new member to the set of known hidden-charm pentaquarks, which includes the $$P_c(4312)$$
 , $$P_c(4440)$$
 and $$P_c(4457)$$
 . The $$P_{cs}(4459)$$
 is expected to have the light-quark content of a $$\Lambda $$
 baryon (
 $$I=0$$
 , $$S=-1$$
 ), but its spin is unknown. Its closeness to the $${\bar{D}}^* \Xi _c$$
 threshold – $$4478\,{\mathrm{MeV}}$$
 in the isospin-symmetric limit – suggests the molecular hypothesis as a plausible explanation for the $$P_{cs}(4459)$$
 . While in the absence of coupled-channel dynamics heavy-quark spin symmetry predicts the two spin-states of the $${\bar{D}}^* \Xi _c$$
 to be degenerate, power counting arguments indicate that the coupling with the nearby $${\bar{D}} \Xi _c'$$
 and $${\bar{D}} \Xi _c^*$$
 channels might be a leading order effect. This generates a hyperfine splitting in which the $$J=\tfrac{3}{2}$$
 $${\bar{D}}^* \Xi _c$$
 pentaquark will be lighter than the $$J=\tfrac{1}{2}$$
 configuration, which we estimate to be of the order of $$5-15\,{\mathrm{MeV}}$$
 . We also point out an accidental symmetry between the $$P_{cs}(4459)$$
 and $$P_c(4440/4457)$$
 potentials. Finally, we argue that the spectroscopy and the $$J/\psi \Lambda $$
 decays of the $$P_{cs}(4459)$$
 might suggest a marginal preference for $$J = \tfrac{3}{2}$$
 over $$J = \tfrac{1}{2}$$
 .

/pdf/the-p-cs-4459-p-cs-4459-pentaquark-from-a-combined-effective-187mlijd6y.pdf

The $$P_{cs}(4459)$$ P cs ( 4459 ) pentaquark from a combined effective field theory and phenomenological perspective

/pdf/chiral-perturbation-theory-for-heavy-hadrons-and-chiral-1c4qehbg.pdf

Chiral perturbation theory for heavy hadrons and chiral effective field theory for heavy hadronic molecules

In this work, we employ the light-cone QCD sum rule to calculate the magnetic dipole moments of the $$P_c(4440)$$
 , $$P_c(4457)$$
 and $$P_{cs}(4459)$$
 pentaquark states by considering them as the diquark–diquark–antiquark and molecular pictures with quantum numbers $$J^P = \frac{3}{2}^-$$
 , $$J^P = \frac{1}{2}^-$$
 and $$J^P = \frac{1}{2}^-$$
 , respectively. In the analyses, we use the diquark–diquark–antiquark and molecular form of interpolating currents, and photon distribution amplitudes to obtain the magnetic dipole moment of pentaquark states. Theoretical examinations on magnetic dipole moments of the hidden-charm pentaquark states, are essential as their results can help us better figure out their substructure and the dynamics of the QCD as the theory of the strong interaction. As a by product, we extract the electric quadrupole and magnetic octupole moments of the $$P_c(4440)$$
 pentaquark. These values show a non-spherical charge distribution.

/pdf/magnetic-dipole-moments-of-the-hidden-charm-pentaquark-zegr289hei.pdf

Magnetic dipole moments of the hidden-charm pentaquark states: $$P_c(4440)$$ P c ( 4440 ) , $$P_c(4457)$$ P c ( 4457 ) and $$P_{cs}(4459)$$ P cs ( 4459 )

Recently, the LHCb Collaboration reported a new structure Pcs(4459) with a mass of 19 MeV below the ΞcD¯* threshold It may be a candidate of molecular state from the ΞcD¯* interaction In the current work, we perform a coupled-channel study of the Ξc*D¯*, Ξc′D¯*, Ξc*D¯, ΞcD¯*, Ξc′D¯, and ΞcD¯ interactions in the quasipotential Bethe-Salpeter equation approach With the help of the heavy quark chiral effective Lagrangian, the potential is constructed by light meson exchanges Two ΞcD¯* molecular states are produced with spin parities JP=1/2- and 3/2- The lower state with 3/2- can be related to the observed Pcs(4450) while two-peak structure cannot be excluded Within the same model, other strange hidden-charm pentaquarks are also predicted Two states with spin parities 1/2- and a state with 3/2- are predicted near the Ξc′D¯, ΞcD¯, and Ξc*D¯ thresholds, respectively As two states near ΞcD¯* threshold, two states are produced with 1/2- and 3/2- near the Ξc′D¯* threshold The couplings of the molecular states to the considered channels are also discussed The experimental research of those states are helpful to understand the origin and internal structure of the Pcs and Pc states

/pdf/p-cs-4459-and-other-possible-molecular-states-from-xi-c-bar-erarrglxa6.pdf

$P_{cs}(4459)$ and other possible molecular states from $\Xi_{c}^{(*)}\bar{D}^{(*)}$ and $\Xi'_c\bar{D}^{(*)}$ interactions

Recently, the LHCb Collaboration reported a new structure ${P}_{cs}(4459)$ with a mass of 19 MeV below the ${\mathrm{\ensuremath{\Xi}}}_{c}{\overline{D}}^{*}$ threshold. It may be a candidate of molecular state from the ${\mathrm{\ensuremath{\Xi}}}_{c}{\overline{D}}^{*}$ interaction. In the current work, we perform a coupled-channel study of the ${\mathrm{\ensuremath{\Xi}}}_{c}^{*}{\overline{D}}^{*}$, ${\mathrm{\ensuremath{\Xi}}}_{c}^{\ensuremath{'}}{\overline{D}}^{*}$, ${\mathrm{\ensuremath{\Xi}}}_{c}^{*}\overline{D}$, ${\mathrm{\ensuremath{\Xi}}}_{c}{\overline{D}}^{*}$, ${\mathrm{\ensuremath{\Xi}}}_{c}^{\ensuremath{'}}\overline{D}$, and ${\mathrm{\ensuremath{\Xi}}}_{c}\overline{D}$ interactions in the quasipotential Bethe-Salpeter equation approach. With the help of the heavy quark chiral effective Lagrangian, the potential is constructed by light meson exchanges. Two ${\mathrm{\ensuremath{\Xi}}}_{c}{\overline{D}}^{*}$ molecular states are produced with spin parities ${J}^{P}=1/{2}^{\ensuremath{-}}$ and $3/{2}^{\ensuremath{-}}$. The lower state with $3/{2}^{\ensuremath{-}}$ can be related to the observed ${P}_{cs}(4450)$ while two-peak structure cannot be excluded. Within the same model, other strange hidden-charm pentaquarks are also predicted. Two states with spin parities $1/{2}^{\ensuremath{-}}$ and a state with $3/{2}^{\ensuremath{-}}$ are predicted near the ${\mathrm{\ensuremath{\Xi}}}_{c}^{\ensuremath{'}}\overline{D}$, ${\mathrm{\ensuremath{\Xi}}}_{c}\overline{D}$, and ${\mathrm{\ensuremath{\Xi}}}_{c}^{*}\overline{D}$ thresholds, respectively. As two states near ${\mathrm{\ensuremath{\Xi}}}_{c}{\overline{D}}^{*}$ threshold, two states are produced with $1/{2}^{\ensuremath{-}}$ and $3/{2}^{\ensuremath{-}}$ near the ${\mathrm{\ensuremath{\Xi}}}_{c}^{\ensuremath{'}}{\overline{D}}^{*}$ threshold. The couplings of the molecular states to the considered channels are also discussed. The experimental research of those states are helpful to understand the origin and internal structure of the ${P}_{cs}$ and ${P}_{c}$ states.

https://link.aps.org/pdf/10.1103/PhysRevD.103.074007

Jun-Tao Zhu

Papers

$P_{cs}(4459)$ and other possible molecular states from $\Xi_{c}^{()}\bar{D}^{()}$ and $\Xi'_c\bar{D}^{(*)}$ interactions

P c s ( 4459 ) and other possible molecular states from Ξ c ( * ) D ¯ ( * ) and Ξ c ′ D ¯ ( * ) interactions