Study of $D_{s}^{+} rightarrow K^{+} K^{-} pi^{+}$ decay

We investigate the $D_{s}^{+} rightarrow K^{+} K^{-} pi^{+}$ decay theoretically with the final state interactions, which is based on the chiral unitary approach and takes into account the external and internal $W$-emission mechanisms at the quark level. Only considering three resonances contributions, the $f_0(980)$ in $S$-wave, the $bar {K}^{*}(892)^{0}$ and $phi(1020)$ in $P$-wave, one can make a good description of the recent experimental data from BESIII Collaboration, where the contribution from $S$-wave is found to be small. Besides, we also make a calculation of the corresponding branching fractions, which are consistent with the results of BESIII Collaboration and Particle Data Group.

Doubly charmed molecular pentaquarks

We perform a systematic exploration of the possible doubly charmed molecular pentaquarks composed of $Sigma_c^{(*)}D^{(*)}$ with the one-boson-exchange potential model. After taking into account the $S-D$ wave mixing and the coupled channel effects, we predict several possible doubly charmed molecular pentaquarks, which include the $Sigma_cD$ with $I(J^P) = 1/2(1/2^-)$, $Sigma_c^*D$ with $1/2(3/2^-)$, and $Sigma_cD^*$ with $1/2(1/2^-)$, $1/2(3/2^-)$. The $Sigma_cD$ state with $3/2(1/2^-)$ and $Sigma_cD^*$ state with $3/2(1/2^-)$ may also be suggested as candidates of doubly charmed molecular pentaquarks. The $Sigma_cD$ and $Sigma_c^*D$ states can be searched for by analyzing the $Lambda_cDpi$ invariant mass spectrum of the bottom baryon and $B$ meson decays. The $Sigma_cD^*$ states can be searched for in the invariant mass spectrum of $Lambda_cD^*pi$, $Lambda_cDpipi$ and $Lambda_cDpigamma$. Since the width of $Sigma_c^*$ is much larger than that of $D^*$, $Sigma_c^*Drightarrow Lambda_cDpi$ will be the dominant decay mode. We sincerely hope these candidates for the doubly charmed molecular pentaqurks will be searched by LHCb or BelleII collaboration in the near future.

Perfect $DD^*$ molecular prediction matching the $T_{cc}$ observation at LHCb

In 2012, we investigated the possible molecular states composed of two charmed mesons [Phys.Rev. D 88, 114008 (2013), arXiv:1211.5007 [hep-ph](2012)]. The $D^*D$ system with the quantum numbers of $I(J^P)=0(1^+)$ was found to be a good candidate of the loosely bound molecular state. This state is very close to the $D^*D$ threshold with a binding energy around 0.47 MeV. This prediction was confirmed by the new LHCb observation of $T_{cc}^+$ [see Franz Muheims talk at the European Physical Society conference on high energy physics 2021].

Magnetic moments and transition magnetic moments of $P_c$ and $P_{cs}$ states

We study the magnetic moments and transition magnetic moments of $P_c$ and $P_{cs}$ states in the molecular picture. We first revisit the magnetic moments of $P_c$ states as the $S$ wave molecular states without coupled channel effects. The coupled channel effects and the $D$ wave contributions are then investigated carefully. The coupled channel effects contribute to the change of $0.1sim 0.4$ nuclear magneton $mu_N$ for most cases while the $D$ wave only induces the variation of less than $0.03 ~mu_N$. In addition, we obtain the transition magnetic moments between different $P_c$ states and the related electromagnetic decay widths of $P_cto P_cgamma$. The magnetic moments of $P_{cs}$ are much different for the assumption of spin being 1/2 and 3/2. The study of electromagnetic properties will help us disclose further the structure of these unconventional states.

Explanation of the newly obseaved $Z_{cs}^-(3985)$ as a $D_s^{(*)-}D^{(*)0}$ molecular state

Inspired by the newly observed $Z_{cs}^-(3985)$ by BESIII collaboration, we study the structure of this particle in the picture of $D_s^{(*)-}D^{(*)0}$ molecular state. Firstly we systematically construct the Lagrangians which describing the interaction of charmed mesons, taking into account the chiral and hidden local symmetries. With the obtained effective potentials from the Lagrangians constructed, we solve the coupled channel Bethe-Salpeter equation with the on-shell approximation. On the third Reimann sheet, a pole position of around $3982.34-i0.53$ MeV is obtained, which can be associated to the $Z_{cs}^-(3985)$ and explained as a loose bound state of $D_s^*bar{D}^*$.

Study $B^{0}_{(s)}$ decays into $phi$ and a scalar or vector meson

In the present work, we investigate the decays of $B^{0}_{s} rightarrow phipi^{+}pi^{-}$ and $B^{0} rightarrow phipi^{+}pi^{-}$ with the final state interactions based on the chiral unitary approach. In the final state interactions of the $pi^+pi^-$ with its coupled channels, we study the effects of the $etaeta$ channel in the two-body interactions for the reproduction of the $f_{0}(980)$ state. Our results for the $pi^+pi^-$ invariant mass distributions of the decay $B^{0}_{s} rightarrow phipi^{+}pi^{-}$ describe the experimental data up to 1 GeV well, with the resonance contributions from the $f_{0}(980)$ and $rho$. For the predicted invariant mass distributions of the $B^{0} rightarrow phipi^{+}pi^{-}$ decay, we found that the contributions from the $f_{0}(500)$ are significant except for the ones from the $f_{0}(980)$ state. With some experimental branching ratios as input to determine the production vertex factors, we make some predictions for the branching ratios of the other final decay channels, including the vector mesons, in the $B^0_{(s)}$ decays, where some of them are consistent with the experimental ones within the uncertainties.

$bar{K}Lambda$ molecular explanation to the newly observed $Xi(1620)^0$

The newly observed $Xi(1620)^0$ by the Belle Collaboration inspires our interest in performing a systematic study on the interaction of an anti-strange meson $(bar{K}^{(*)})$ with a strange or doubly strange ground octet baryon $mathcal{B}$ ($Lambda$, $Sigma$, and $Xi$), where the spin-orbit force and the recoil correction are considered in the adopted one-boson-exchange model. Our results indicate that $Xi(1620)^0$ can be explained as a $bar{K}Lambda$ molecular state with $I(J^P)=1/2(1/2^-)$ and the intermediate force from $sigma$ exchange plays an important role. Additionally, we also predict several other possible molecular candidates, i.e., the $bar{K}Sigma$ molecular state with $I(J^P)=1/2(1/2^-)$ and the triply strange $bar{K}Xi$ molecular state with $I(J^P)=0(1/2^-)$.

Strong LHCb evidence supporting the existence of the hidden-charm molecular pentaquarks

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.

Possible bound states with hidden bottom from $bar{K}^{(*)}B^{(*)}bar{B}^{(*)}$ systems

We study the three-body systems of $bar{K}^{(*)}B^{(*)}bar{B}^{(*)}$ by solving the Faddeev equations in the fixed-center approximation, where the light particle $bar{K}^{(*)}$ interacts with the heavy bound states of $Bbar{B}$ ($B^*bar{B}^*$) forming the clusters. In terms of the very attractive $bar{K}^*B$ and $bar{K}^*B^*$ subsystems, which are constrained by the observed $B_{s1}(5830)$ and $B_{s2}^*(5840)$ states in experiment, we find two deep bound states, containing the hidden-bottom components, with masses $11002pm 63$ MeV and $11078pm 57$ MeV in the $bar{K}^*Bbar{B}$ and $bar{K}^*B^*bar{B}^*$ systems, respectively. The two corresponding states with higher masses of the above systems are also predicted. In addition, using the constrained two-body amplitudes of $bar{K}B^{(*)}$ and $bar{K}bar{B}^{(*)}$ via the hidden gauge symmetry in the heavy-quark sector, we also find two three-body $bar{K}Bbar{B}$ and $bar{K}B^{*}bar{B}^*$ bound states.

Constructing new pseudoscalar meson nonets with the observed $X(2100)$, $X(2500)$, and $eta(2225)$

Stimulated by the BESIII observation of $X(2100)$, $X(2500)$, and $eta(2225)$, we try to pin down new pseudoscalar meson nonets including these states. The analysis of mass spectra and the study of strong decays indicate that $X(2120)$ and $eta(2225)$ associated with $pi(2070)$ and the predicted kaon $K(2150)$ may form a new pseudoscalar meson nonet. In addition, more experimental data for $X(2100)$ are necessary to determine its structure of nonets. Then, $X(2500)$, $X(2370)$, $pi(2360)$, and the predicted kaon $K(2414)$ can be grouped into another new nonet. These assignments to the discussed pseudoscalar states can be further tested in experiment.