Exotic ■_s~((*))D~((*)) molecular states and sc■ tetraquark states with J~P=0~+,1~+,2~+

We have calculated the mass spectra for the ■_s~((*))D~((*)) molecular states and sc■ tetraquark states with J~P=0~+,1~+,2~+.The masses of the axial-vector ■_sD~*,■_s~*D molecular states and ■ tetraquark states are predicted to be approximately 3.98 GeV,in good agreement with the mass of Z_(cs)(3985)~- from BESⅢ.In both the molecular and diquark-antidiquark scenarios,our results suggest that there may exist two almost degenerate states,as the strange partners of X(3872) and Z_c(3900).We propose to carefully examine Z_(cs)(3985) in future experiments to verify this.One may also search for more hidden-charm four-quark states with strangeness in not only the open-charm ■_s~((*))D~((*)) channels but also the hidden-charm channels η_cK/K~*,J/ψK/K~*.     

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.     

A note on the B*B,B*B*,D*,D** molecular states

In the framework of the one-boson-exchange model, we have performed an extensive study of the possible B*B,B*B*,D*,D** molecular states with various quantum numbers after considering the S-wave and D-wave mixing. We also discuss the possible experimental research of these interesting states.     

Search for the doubly heavy baryons Ω_(bc)~0 and Ξ_(bc)~0 decaying to Λ_c~+π~- and Ξ_c~+π~-

The first search for the doubly heavy Ω_(bc)~0 baryon and a search for the Ξ_(bc)~0 baryon are performed using pp collision data collected via the LHCb experiment from 2016 to 2018 at a centre-of-mass energy of 13 TeV,corresponding to an integrated luminosity of 5.2 fb~(-1).The baryons are reconstructed via their decays to ∧_c~+π~-andΞ_c~+π~-.No significant excess is found for invariant masses between 6700 and 7300 MeV/c2,in a rapidity range from2.0 to 4.5 and a transverse momentum range from 2 to 20 MeV/c.Upper limits are set on the ratio of the Ω_(bc)~0 andΞ_(bc)~0 production cross-section times the branching fraction to ∧_c~+π~-(Ξ_c~+π~-) relative to that of the ∧_b~0(Ξ_b~0) baryon,for different lifetime hypotheses,at 95% confidence level.The upper limits range from 0.5×10~(-4) to 2.5×10~(-4) for theΩ_(bc)~0→∧_c~+π~-(Ξ_(bc)~0→∧_c~+π~-) decay,and from 1.4×10~(-3) to 6.9×10~(-3) for the Ω_(bc)~0→Ξ_c~+π~-(Ξ_(bc)~0→Ξ_c~+π~-) decay,depending on the considered mass and lifetime of the Ω_(bc)~0(Ξ_(bc)~0) baryon.     

Electromagnetic form factors of Λ_c in the space-like momentum region

We studied the electromagnetic form factors(EMFFs) of Λ_c and the contributions of the quark and diquark currents to the EMFFs of Λ_c in the space-like region in the Bethe–Salpeter equation approach with instantaneous approximation. In this picture, baryon Λ_c can be regarded as a two-body c(ud) system. We found that for different values of parameters the contribution of quark and diquark currents to the EMFFs of Λ_c is very different,while their total contribution to the EMFFs of Λ_c is similar. The EMFFs of Λ_c are similar to those of other baryons(proton, Ξ~-, and Σ~+) with a peak at ω = 1, where ω = v′·v is the velocity transfer between the initial state(with velocity v) and the final state(with velocity v′) of Λ_c.     

Strong decays of the low-lying bottom strange baryons

In this work,the strong decay behaviors of the λ-mode low-lying Ξ_b and Ξ'_b baryons are investigated within the ~3 P_0 model.Our results suggest that all of the low-lying 3_F states Ξ_b(2 S),Ξ_b(1 P),and Ξ_b(1 D) have small decay widths of less than 20 MeV,and these states have good potentials to be observed in the Ξ'_bπ and Ξ'_b~*π invariant masses.Further,most of the 6_F multiplets are relatively narrow and may decay into the Ξ_bπ,Ξ'_bπ,Ξ'_b~*π,and Δ_bK final states.Considering the masses and strong decay behaviors,we can assign the newly observed Ξ_b(6100) resonance as the Ξ_b(1 P) state with J~P=3/2~-and interpret the Ξ_b(6227)structure as the J~P=3/2~-Ξ'_b(1 P) state with a proper mixing angle.We expect that our predictions for these excited bottom strange baryons will provide helpful information for future experimental research.     

Weak decays of doubly heavy baryons: “decay constants”

Inspired by the recent observation of the Ξ_c~+_c~+)by the LHCb Collaboration, we explore the "decay constants" of doubly heavy baryons in the framework of QCD sum rules. With the Ξ_cc),Ξ_(bc),Ξ_(bb), and ?_(cc),?_(bc),?_(bb) baryons interpolated by three-quark operators, we calculate the correlation functions using the operator product expansion and include the contributions from operators up to dimension six. On the hadron side, we consider both contributions from the lowest-lying states with JP=1/2~+ and from negative parity baryons with JP=1/2~-. We find that the results are stable and the contaminations from negative parity baryons are not severe. These results are ingredients for the QCD study of weak decays and other properties of doubly-heavy baryons.     

Analysis of the Y(4220) and Y(4390) as molecular states with QCD sum rules

In this article, we assign the Y(4390) and Y(4220) to be the vector molecular states D_1(2420) and D* *_0(2400), respectively, and study their masses and pole residues in detail with the QCD sum rules. The present calculations only favor assigning the Y(4390) to be the D_1(1~(--)) molecular state.     

Radiative decay of the Ξ(1620) in a hadronic molecule picture

Last year,the Ξ(1620) state,which is cataloged in the Particle Data Group(PDG) with only one star,was reported again in the Ξ~-π~+final state by the Belle Collaboration.Its properties,such as the spectroscopy and decay width,cannot be simply explained in the context of conventional constituent quark models.This inspires an active discussion on the structure of this resonance.In this paper,we study the radiative decays of the newly observed Ξ(1620) assuming that it is a meson-baryon molecular state of AK and with spin-parity J~P=1/2~-developed in our previous study.The partial decay widths of the AK-ΣK molecular state into Ξγ and Ξπγ final states through hadronic loops are evaluated using effective Lagrangians.The partial widths for Ξ(1620)~0→γΞ is evaluated to be approximately 118.76-174.21 keV,which may be accessible for the LHCb experiment.If Ξ(1620) is aΛK-∑K molecule,the radiative transition strength Ξ(1620)~0→γKA is considerably small and the decay width is of the order of 0.01 eV.Future experimental measurements of these processes can be useful to test the molecule interpretations of the Ξ(1620).     

Search for the doubly charmed baryon ■

A search for the doubly charmed baryon Ξ_(cc)~+ is performed through its decay to the Λ_c~+K~-π~+ final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 Te V. The data correspond to a total integrated luminosity of 9 fb~(-1). No significant signal is observed in the mass range from 3.4 to 3.8 Ge V/c~2. Upper limits are set at 95% credibility level on the ratio of the Ξ_(cc)~+ production cross-section times the branching fraction to that of Λ_c~+ and Ξ_(cc)~(++) baryons. The limits are determined as functions of the Ξ_(cc)~+ mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15 GeV/c.     

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~-.     

Evidence for the decays of ∧_c~+→∑~+η and ∑~+η'

We study the hadronic decays of ∧_c~+ to the final states ∑~+η and ∑~+η',using an e~+e~-annihilation data sample of 567 pb~(-1) taken at a center-of-mass energy of 4.6 GeV with the BESIII detector at the BEPCⅡ collider.We find evidence for the decays ∧_c~+→∑~+η and ∑~+η' with statistical significance of 2.5σ and 3.2σ,respectively.Normalizing to the reference decays ∧_c~+→∑~+π0 and ∑~+ω,we obtain the ratios of the branching fractions■and ■to be 0.35±0.16±0.02 and 0.86±0.34±0.04,respectively.The upper limits at the 90% confidence level are set to be■and■.Using BESIII measurements of the branching fractions of the reference decays,we determine B(∧_c~+→∑~+η)=(0.41±0.19±0.05)%(0.68%)and B(∧_c~+→∑~+η')=(1.34±0.53 ±0.19)%(1.9%).Here,the first uncertainties are statistical and the second systematic.The obtained branching fraction of ∧_c~+→∑~+η is consistent with the previous measurement,and the branching fraction of ∧_c~+→∑~+η' is measured for the first time.     

The D~* interaction with isospin zero in an extended hidden gauge symmetry approach

The D~* interaction via a ρ or ω exchange is constructed within an extended hidden gauge symmetry approach, where the strange quark is replaced by the charm quark in the SU(3) flavor space. With this D~*interaction, a bound state slightly lower than the D~* threshold is generated dynamically in the isospin zero sector by solving the Bethe-Salpeter equation in the coupled-channel approximation, which might correspond to the X(3872)particle announced by many collaborations. This formulism is also used to study the BB~* interaction, and a BB~* bound state with isospin zero is generated dynamically, which has no counterpart listed in the review of the Particle Data Group. Furthermore, the one-pion exchange between the D meson and the ~* is analyzed precisely, and we do not think the one-pion exchange potential need be considered when the Bethe-Salpeter equation is solved.     

Effect of the mesons σ~＊ and Φ and the variety of U_Σ~（N） on the transition density of hyperon stars

The effect of the mesons σ＊ and Φ and the variety of UΣ（N ）on the transition density of hyperon stars is examined within the framework of relativistic mean field theory for the baryon octet {n,p,Λ,Σ-,Σ0,Σ＋,Ξand Ξ0} system.It is found that,compared with that without considering the mesons σ＊ and Φ,the transition density of hyperon stars decreases,the critical baryon density that hyperons Σ-,Σ0,Σ＋,Ξand Ξ0 appears to decrease too,but for Λ the effect is not obvious.As U Σ（N ）goes up,the critical baryon density of Σ＋,Σ0 and Σincreases,that of Ξ0 decreases and that of Λ and Ξis fixed.In addition,it is found that the variety of UΣ（N ）almost does not influence the transition density.     

Study of Σ~*-Δ Interactions

We study the Σ~*-Δ interaction in the chiral SU(3) quark model and in the extended chiral SU(3) quark model.In these two models,the short-range interaction mechanism are totally different,one is from the one-gluon exchange and another is from the vector meson exchange.The possible reasons of forming strangeness-1 bound states are given.Comparisons between the cases with and without quark exchange effect are made.The results show the quark exchange effect does give attractions to (Σ~*Δ)_(ST)=0 5/2 and (Σ~*Δ)_(ST)=3 1/2 systems,which means the special symmetry is important.Also,we make some analysis on chiral field effect,our results show that the σ exchange dominantly provides the attractive interaction for these two states.     

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.     

Equilibrium dynamics of the sub-Ohmic spin-boson model under bias

Using the bosonic numerical renormalization group method, we studied the equilibrium dynamical correlation function C(ω) of the spin operator σ_z for the biased sub-Ohmic spin-boson model. The small-ω behavior C(ω) ∝ω~s is found to be universal and independent of the bias ε and the coupling strength α(except at the quantum critical point α = αc and ε = 0). Our NRG data also show C(ω) ∝χ~2ω~s for a wide range of parameters, including the biased strong coupling regime(ε = 0 and α α_c), supporting the general validity of the Shiba relation. Close to the quantum critical point αc,the dependence of C(ω) on α and ε is understood in terms of the competition between ε and the crossover energy scale ω_0~*of the unbiased case. C(ω) is stable with respect to ε for ε《ε~*. For ε》ε~*, it is suppressed by ε in the low frequency regime. We establish that ε~*∝(ω_0~*)~(1/θ)holds for all sub-Ohmic regime 0≤s 1, with θ = 2/(3s) for 0 s≤1/2 and θ = 2/(1 + s) for 1/2 s 1. The variation of C(ω) with α and ε is summarized into a crossover phase diagram on the α–ε plane.     

Search for the doubly charmed baryon ?_(cc)~+

A search for the doubly charmed baryon ?_(cc)~+ with the decay mode ?_(cc)~+→Ξ_c~+K~-π~+ is performed using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4 fb~(-1). No significant signal is observed within the invariant mass range of 3.6 to 4.0 GeV/c~2. Upper limits are set on the ratio R of the production cross-section times the total branching fraction of the ?_(cc)~+→Ξ_c~+K~-π~+ decay with respect to the Ξ_(cc)~(++)→Λ_c~+K~-π~+π~+ decay. Upper limits at 95% credibility level for R in the range 0.005 to 0.11 are obtained for diferent hypotheses on the ?_(cc)~+ mass and lifetime in the rapidity range from 2.0 to 4.5 and transverse momentum range from 4 to 15 GeV/c.     

CHARMED BARYONS(C=+1)∧_c~+=udc,∑_c~(++)=uuc,∑_c~+=udc,∑_c~0=ddc,≡_c~+=usc,≡_c~0=dsc,Ω_c~0=ssc

<正>CHARMED BARYONS Revised March 2012 by C.G.Wohl(LBNL).There arc 17 known charmed baryons,and four other candidates not well enough established to be promoted to the Summary Tables.*Fig.1(a)shows the mass spectrum,and for comparison Fig.1(b)shows the spectrum of the lightest strange baryons.The∧_c and∑_c spectra ought to look much like the A and∑spectra,since a∧_c or a∑_c differs from a A or a E only by the replacement of the s quark with a c quark.However,a 3 or anΩhas more than one s quark,only one of which is changed to a c quark to make aΞ_c or anΩ_c.Thus theΞ_C andΩ_c spectra ought to be richer than the E and$2 spectra.**