Analysis of Z_(cs)(3985) as the axialvector tetraquark state

In this study,we choose the scalar and axialvector diquark operators in the color antitriplet as the fundamental building blocks to construct four-quark currents and investigate the diquark-antidiquark type axialvector tetraquark states ccus in the framework of the QCD sum rules.The predicted tetraquark mass M_Z=3.99±0.09 GeV is in excellent agreement with the experimental value 3985.2_(-2.0)~(+2.1)±1.7 MeV from the BESⅢ collaboration,which supports identifying Z_(cs)(3985) as the cousin of Zc(3900) with quantum numbers J~(PC)=1~(+-).We take into account the light flavor S U(3) mass-breaking effect to estimate the mass spectrum of the diquark-antidiquark type hidden-charm tetraquark states with strangeness according to previous studies.     

Investigation of the tetraquark states ■ in the improved chromomagnetic interaction model

In the framework of the improved chromomagnetic interaction model, we complete a systematic study of the S-wave tetraquark states ■ ( Q = c, b, and q = u, d, s) with different quantum numbers: J^PC= 0⁽+(+)), 1⁽+(±)),and 2⁽+(+)). The mass spectra of tetraquark states are predicted, and the possible decay channels are analyzed by considering both the angular momentum and C-parity conservation. The recently observed hidden-charm tetraquark states with stra...     

Possible strange hidden-charm pentaquarks from Σ_c~((*))_s~* and Ξ_c~((',*))~* interactions

Using the one-boson-exchange model, we investigate the Λ_c_s~*, Σ_c_s~*, Σ_c~*_s~*, Ξ_c~*, Ξ'_c~*, and Ξ_c~*~* 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'_c~* state with 0((1/2)~-) and the Ξ_c~*~* 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.     

A family of double-beauty tetraquarks: Axial-vector state ■

The spectroscopic parameters and decay channels of the axial-vector tetraquark ■(in what follows,■ are explored using the quantum chromodynamics(QCD) sum rule method.The mass and coupling of this state are calculated using two-point sum rules by taking into account various vacuum condensates,up to 10 dimensions.Our prediction for the mass of this state m=(10215±250) MeV confirms that it is stable with respect to strong and electromagnetic decays and can dissociate to conventional mesons only via weak transformations.We investigate the dominant semileptonic ■ and nonleptonic ■ decays of ■.In these processes,■ is a scalar tetraquark ■ built of a color-triplet diquark and an antidiquark,whereas M is one of the vector mesons ρ~-,K~*(892),D~*(2010)~-,and D_s~(*-).To calculate the partial widths of these decays,we use the QCD three-point sum rule approach and evaluate the weak transition form factors G_i(i=0,1,2,3),which govern these processes.The full width Γ_(full)=(12.9±2.1) × 10~(-8) MeV and the mean lifetime τ=5.1+_(-0.71) ~(+0.99) fs of the tetraquark ■ are computed using the aforementioned weak decays.The obtained information about the parameters of ■ and ■ is useful for experimental investigations of these double-heavy exotic mesons.     

The ■ tetraquark states and the structure of X(2239) observed by the BESⅢ collaboration

We investigate the mass spectrum of the■tetraquark states in the relativized quark model.By solving the Schrodinger-like equation with the relativized potential,the masses of S-and P-wave■tetraquarks are obtained.The screening effects are also taken into account.It is found that the resonant structureX(2239)observed in thee+e-→K+K-process by the BESIII collaboration can be assigned as a P-wave 1--■tetraquark state.Furthermore,the radiative transition and the strong decay behavior of this structure are also estimated,which can provide helpful information for future experimental searches.     

Scalar Hidden-Charm Tetraquark States with QCD Sum Rules

In this article, we study the masses and pole residues of the pseudoscalar-diquark-pseudoscalar-antidiquark type and vector-diquark-vector-antidiquark type scalar hidden-charm cud(cus) tetraquark states with QCD sum rules by taking into account the contributions of the vacuum condensates up to dimension-10 in the operator product expansion.The predicted masses can be confronted with the experimental data in the future. Possible decays of those tetraquark states are also discussed.     

D-wave excited ■ tetraquark states with JPC=1++ and 1+-

We study the mass spectra of D-wave excited cscs tetraquark states with J^PC=1⁺⁺ and 1^+- in both symmetric ■ and antisymmetric ■ color configurations using the QCD sum rule method.We construct the D-wave diquark-antidiquark type of cscs tetraquark interpolating currents in various excitation structures with(L_λ,L_ρ(l_p1,l_ρ2))=(2,0{0,0)),(1,1{1,0)),(1,1{0,1)),(0,2{1,1)),(0,2{2,0}),(0,2{0,2}).Our results support the interpret...     

A note on ■_c(3055)~ and ■_c(3123)~

The Babar Collaboration announced two new excited charmed baryons■_c(3055)~ and■_c(3123)~ . We study their strong decays assuming they are D-wave states.Some assignments are excluded by comparing our numerical results with the experimental values of the total widths of ■_c(3055)~ and■_c(3123)~ .We also suggest some possible decay modes,which will be helpful to determine the properties of■_c(3055)~ and■_c(3123)~ .     

Prediction of possible exotic states in the η■K~* system

We investigate the ηKK~*three-body system in order to look for possible IG(J~(PC))=0~+(1~(-+)) exotic states in the framework of the fixed-center approximation of the Faddeev equation.We assume the scattering of η on a clusterized system KK~*,which is known to generate f_1(1285),or a K in a clusterized system ηK~*,which is shown to generate K_1(1270).In the case of η-(KK~*)f_1(1285) scattering,we find evidence of a bound state IG(J~(PC))=0~+(1~(-+)) below theηf_1(1285) threshold with a mass of around 1700 MeV and a width of about 180 MeV.Considering K-(η/K~*)K_1(1270)scattering,we obtain a bound state I(J~P)=0(1~-) just below the KK_1(1270) threshold with a mass of around 1680 MeV and a width of about 160 MeV.     

Analysis of the tetraquark and hexaquark molecular states with the QCD sum rules

In this article, we construct the color-singlet-color-singlet type currents and the color-singlet-colorsinglet-color-singlet type currents to study the scalar D*■*, D*D* tetraquark molecular states and the vector D*D*■*, D*D*D* hexaquark molecular states with the QCD sum rules in details. In calculations, we choose the pertinent energy scales of the QCD spectral densities with the energy scale formula ■for the tetraquark and hexaquark molecular states respectively in a consistent way. We obtain stable QCD sum rules for the scalar D*■*, D*D*tetraquark molecular states and the vector D*D*■* hexaquark molecular state, but cannot obtain stable QCD sum rules for the vector D*D*D* hexaquark molecular state. The connected(nonfactorizable)Feynman diagrams at the tree level(or the lowest order) and their induced diagrams via substituting the quark lines make positive contributions for the scalar D*D* tetraquark molecular state, but make negative or destructive contributions for the vector D*D*D* hexaquark molecular state. It is of no use or meaningless to distinguish the factorizable and nonfactorizable properties of the Feynman diagrams in the color space in the operator product expansion so as to interpret them in terms of the hadronic observables, we can only obtain information about the short-distance and long-distance contributions.     

Searching for high-K isomers in the proton-rich A～80 mass region

Configuration-constrained potential-energy-surface calculations have been performed to investigate the K isomerism in the proton-rich A～ 80 mass region. An abundance of high-K states are predicted. These high-K states arise from two and four-quasi-particle excitations, with K~π= 8~+ and K~π= 16~+, respectively. Their excitation energies are comparatively low, making them good candidates for long-lived isomers. Since most nuclei under study are prolate spheroids in their ground states, the oblate shapes of the predicted high-K states may indicate a combination of K isomerism and shape isomerism.     

Neural network study of hidden-charm pentaquark resonances

Recently,the LHCb experiment announced the observation of hidden-charm pentaquark states P,(4312),P_c(4440),and P_c(4457)near Σ_cD and Σ_cD~* thresholds.In this present work,we studied these pentaquarks in the framework of the nonrelativistic quark model with four types of potential.We solved five-body Schrodinger equation by using the artificial neural network method and made predictions of parities for these states,which are not yet determined by experiment.The mass of another possible pentaquark state near the D~*Σ_c~* with J~P=5/2~-is also calculated.     

Properties of the P_c(4312) pentaquark and its bottom partner

We present an analysis of the newly observed pentaquark P_c(4312)~+ to shed light on its quantum numbers.To do that,the QCD sum rules approach is used.The measured mass of this particle is close to the ∑_c~(++)D~-threshold and has a small width,which supports the possibility of its being a molecular state.We consider an interpolating current in a molecular form and analyze both the positive and negative parity states with spin-1/2.We also consider the bottom counterpart of the state with similar molecular form.Our mass result for the charm pentaquark state supports that the quantum numbers of the observed state are consistent with J~P=1/2~-.     

Molecular picture for X_0(2900) and X_1(2900)

Inspired by the newly observed X_0(2900) and X_1(2900) states at LHCb,the K~*■ and K■ interactions are studied in the quasipotential Bethe-Salpeter equation approach combined with the one-bo son-exchange model.The bound and virtual states from the interactions are searched for as poles in the complex energy plane of scattering amplitude.A bound state with I(J~P)=0(0~+) and a virtual state with 0(1~-) are produced from the K~*■ interaction and K■ interaction,and can be related to the X_0(2900) and X_1(2900) observed at LHCb,respectively.A bound state with I(J~P)=0(1~+) and a virtual state with I(J~P)=0(2~+) are also predicted from the K~*■ interaction,with the same α value,to reproduce the X_(0,1)(2900),which can be searched for in future experiments.     

Polaron and molecular states of a spin–orbit coupled impurity in a spinless Fermi sea

We investigate the polaron and molecular states of a fermionic atom with one-dimensional spin–orbit coupling(SOC)coupled to a three-dimensional spinless Fermi sea. Because of the interplay among the SOC, Raman coupling and spinselected interatomic interactions, the polaron state induced by the spin–orbit coupled impurity exhibits quite unique features. We find that the energy dispersion of the polaron generally has a double-minimum structure, which results in a finite center-of-mass(c.m.) momentum in the ground state, different from the zero-momentum polarons where SOC are introduced into the majority atoms. By further tuning the parameters such as the atomic interaction strength, a discontinuous transition between the polarons with different c.m. momenta may occur, signaled by the singular behavior of the quasiparticle residue and effective mass of the polaron. Meanwhile, the molecular state as well as the polaron-to-molecule transition is also strongly affected by the Raman coupling and the effective Zeeman field, which are introduced by the lasers generating SOC on the impurity atom. We also discuss the effects of a more general spin-dependent interaction and mass ratio. These results would be beneficial for the study of impurity physics brought by SOC.     

Ξ_(bb) and Ω_(bbb) molecular states

Using the vector exchange interaction in the local hidden gauge approach,which in the light quark sector generates the chiral Lagrangians and has produced realistic results for ?_c,Ξ_c,Ξ_b and the hidden charm pentaquark states,we study the meson-baryon interactions in the coupled channels that lead to the Ξ_(bb) and ?_(bbb) excited states of the molecular type.We obtain seven states of the Ξ_(bb) type with energies between 10408 and 10869 MeV,and one ?_(bbb) state at 15212 MeV.     

Pure annihilation decays of B_s~0→a_0~+a_0~- and B_d~0→K_0~(*+)K_0~(*-) in the PQCD approach

We study the CP-averaged branching fractions and the CP-violating asymmetries in the pure annihilation decays ofB _s~0→a_0~+a _0~-andB _d~0→K_0~(*+)K_0~(*-),where a_0[K_0~*]denotes the scalar a_0(980) and a_0(1450)[K_0~*(800)(ork)and K_0~*(1430)],with the perturbative QCD factorization approach under the assumption of two-quark structure for the a_0and K_0~*states.The numerical results show that the branching ratios of theB _d~0→K_0~(*+)K_0~(*-)decays are in the order of 10~(-6),while the decay rates of theB_s~0→a_0~+a _0~-modes are in the order of 10~(-5).In light of the measured modes with the same quark components in the pseudoscalar sector,namely,B _d~0→K~+K~-and B_s~0→p p~(+-),the predictions for the considered decay modes in this work are expected to be measured at the Large Hadron Collider beauty and/or Belle-Ⅱ experiments in the (near) future.Meanwhile,it is of great interest to find that the twist-3 distribution amplitudes φ~S and φ~T with inclusion of the Gegenbauer polynomials for the scalar a_0(1450) and K_0~*(1430)states in scenario2 contribute slightly to the branching ratios while significantly to the CP violations in the B_d~0→K_0~*(14 30)~+K_0*(14 30)~-and B_s~0→a_0(1450)~+a_0(1450)~-decays,which indicates that,compared to the asymptotic φ~Sand φ~T,these Gegenbauer polynomials could change the strong phases evidently in these pure annihilation decay channels.These predictions await for the future confirmation experimentally,which could further provide useful information to help explore the inner structure of the scalars and shed light on the annihilation decay mechanism.     

Semileptonic decays B/B_s→(D~((*)),D_s~((*))lv_l in the PQCD approach with the lattice QCD input

We study the semileptonic B/B_s→(D~((*)),D_s~((*)))lv_l decays in the framework of the Standard Model(SM),by employing the perturbative QCD(PQCD) factorization formalism combined with the lattice QCD input for the relevant transition form factors.We calculate the branching ratios B(B_((s))→D_((s))~((*))lv_l) with l=(e,μ,τ),the ratios of the branching fractions R(D~((*))) and R(D_s~((*))),and the physical observables P_τ(D_((s))~((*))),F_L(D_((s))~*) and A_(FB)(τ).The "PQCD+Lattice" predictions for B(B→D~((*))lv_l) and R(D~((*))) agree with the available experimental measurements within errors.For the ratios R(D_s) and R(D_s~*),the "PQCD+Lattice" predictions agree with the other predictions.For P_τ(D~*) and F_L(D~*),our theoretical predictions agree with the measured values within errors.Our theoretical predictions of the semileptonic B/B_s decays considered could be tested in the near future by the LHCb and Belle Ⅱ experiments.     

A method for measuring D~* electromagnetic form factors in e~+e~- annihilation

We describe a method for measuring the electromagnetic form factors of the D~* meson at time-like momentum transfer in e~+e~-annihilation.This is to study the joint angular distribution of the e~+e~-→γ~*→D~*+D~*-,D~*~+→D~0π~+,and D~*-→D~0π-processes.The magnitudes and relative phases of the charge,magnetic and quadrupole form factors can be determined.The method can also be applied to other vector particles.