The LHCb Collaboration at the Large Hadron Collider at CERN discovered two pentaquark states P_{c}(4380) and P_{c}(4450). These two hidden-charm states are interpreted as the loosely bound Σ_{c}(2455)D^{*} and Σ_{c}^{*}(2520)D^{*} molecular states in the boson exchange interaction model, which provides an explanation for why the experimental width of P_{c}(4450) is much narrower than that of P_{c}(4380). The discovery of the new resonances P_{c}(4380) and P_{c}(4450), indeed, opens a new page for hadron physics. The partners of P_{c}(4380) and P_{c}(4450) should be pursued in future experiments.

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 Σ c and an S-wave anti-charmed meson (D,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 Σ cD with (I = 1/2, J P = 1/2 − ), Σ cD * with (I = 1/2, J P = 1/2 − ) and Σ cD * with (I = 1/2, J P = 3/2 − ), respectively.

Using the one-boson-exchange model, we investigate the Λ interactions by considering the one-eta-exchange and/or one-pion-exchange contributions. We further predict the existence of hidden-charm molecular pentaquarks. Promising candidates for hidden-charm molecular pentaquarks include a Ξ ′ cD * state with 0( 1 2 − ) and the Ξ * cD * states with 0( 1 2 − ) and 0( 3 2 − ). Experimental searches for these predicted hidden-charm molecular pentaquarks are an interesting future research topic for experiments like LHCb.

The magnetic moment of a baryon state is an equally important dynamical observable as its mass, which encodes crucial information of its underlying structure. According to the different color-flavor structure, we have calculated the magnetic moments of the hidden-charm pentaquark states with the isospin (I, I 3 ) = ( + in the molecular model, the diquark-triquark model, and the diquark-diquark-antiquark model, respectively. Although a good description for the pentaquark mass spectrum and decay patterns has been obtained in all three models, different color-flavor structures lead to different magnetic moments, which can be used to pin down their inner structures and distinguish various models.

In a one-boson-exchange model, we study molecular states of double-charm baryon ($\Xi_{cc}(3621)$) and a charmed meson ($D$ and $D^*$). Our model indicates that there exist two possible triple-charm molecular pentaquarks, a $\Xi_{cc}D$ state with $I(J^P)=0(1/2^-)$ and a $\Xi_{cc}D^*$ state with $I(J^P)=0(3/2^-)$. In addition, we also extend our formula to explore $\Xi_{cc}\bar{B}^{(*)}$, $\Xi_{cc}\bar{D}^{(*)}$, and $\Xi_{cc}B^{(*)}$ systems, and find more possible heavy flavor molecular pentaquarks, a $\Xi_{cc}\bar{B}$ state with $I(J^P)=0(1/2^-)$, a $\Xi_{cc}\bar{B}^*$ state with $I(J^P)=0(3/2^-)$, and $\Xi_{cc}\bar{D}^*/\Xi_{cc}B^*$ states with $I(J^P)=0(1/2^-)$. Experimental search for these predicted triple-charm molecular pentaquarks is encouraged.Comment: 6 pages, 4 figure

Inspired by the observations of three P c states, we systematically investigate interactions between an S-wave charmed baryon B (*) c = c / c / * c and an anticharmed mesonT =D 1 /D * 2 with the one-pion-exchange potential model and the one-boson-exchange potential model, and search for possible new types of P c states with the structures of B (*) cT. Both S-D wave mixing and coupled channel effects are considered. Our results suggest that in some B (*) cT systems there are ideal candidates of new types of P c states-i.e., the cD1 state with I (J P) = 1/2(1/2 +), the cD * 2 state with I (J P) = 1/2(3/2 +), the * cD 1 state with I (J P) = 1/2(1/2 +), and the * cD * 2 states with I (J P) = 1/2(1/2 + , 3/2 +)-and we suggest that these predicted new types of P c states can be detected in the process 0 b → ψ (2S)pπ −. Meanwhile, we also extend our study to the interactions between an S-wave charmed baryon and a charmed meson in a T doublet, and we predict a series of double-charm molecular pentaquarks.

Adopting the one-boson-exchange model, we perform a systematic investigation of interactions between a doubly charmed baryon ðΞ cc Þ and an S-wave charmed baryon (Λ c , Σ ðÃÞ c , and Ξ ð0;ÃÞ c ). Both the SÀD mixing effect and coupled-channel effect are considered in this work. Our results suggest that there may exist several possible triple-charm deuteronlike hexaquarks. Meanwhile, we further study the interactions between a doubly charmed baryon and an S-wave anticharmed baryon. We find that a doubly charmed baryon and an Swave anticharmed baryon can be easily bound together to form shallow molecular hexaquarks. These heavy flavor hexaquarks predicted here can be accessible at future experiment like LHCb.

Stimulated by the observations of recent observation of Ω c as well as former one of P c (4380) and P c (4450), we perform a coupled channel analysis of/Ω c ω systems to search for possible Ω c −like molecular states by using a one-boson-exchange potential. Our results suggest there exists a loosely bound molecular state, ait is mainly composed of the Ξ * c K system. Two-body strong decay width is also studied, where we find that Ξ ′ c K is the dominant decay channel.