arXiv subjects

Hua-Xing Chen

Publications and source records attributed to Hua-Xing Chen.

At least 91 records · Page 5Linked to original sources

arXiv2020

$P$-wave bottom baryons of the $SU(3)$ flavor $\mathbf{6}_F$

We investigate $P$-wave bottom baryons of the $SU(3)$ flavor $\mathbf{6}_F$, and systematically study their $D$-wave decays into ground-state bottom baryons and pseudoscalar mesons. Together with [PRD91, 054034 (2015); PRD92, 114007 (2015); PRD95, 094008 (2017); EPJC80, 80 (2020)], a rather complete study is performed on both mass spectra and decay properties of $P$-wave bottom baryons, using the method of QCD sum rules and light-cone sum rules within the framework of heavy quark effective theory. Among all the possibilities, we find four $Σ_b$, four $Ξ^\prime_b$, and six $Ω_b$ baryons, with limited widths and so capable of being observed. Their masses, mass splittings within the same multiplets, and decay properties are extracted (summarized in Table V) for future experimental searchings.

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arXiv2020

$X_0(2900)$ and $X_1(2900)$: hadronic molecules or compact tetraquarks

Very recently the LHCb Collaboration reported their observation of the first two fully open-flavor tetraquark states, the $X_0(2900)$ of $J^P = 0^+$ and the $X_1(2900)$ of $J^P = 1^-$. We study their possible interpretations using the method of QCD sum rules, paying special attention to an interesting feature of this experiment that the higher resonance $X_1(2900)$ has a width significantly larger than the lower one $X_0(2900)$. Our results suggest that the $X_0(2900)$ can be interpreted as the $S$-wave $D^{*-}K^{*+}$ molecule state of $J^P = 0^+$, and the $X_1(2900)$ can be interpreted as the $P$-wave $\bar c \bar s u d$ compact tetraquark state of $J^P = 1^-$. Mass predictions of their bottom partners are also given.

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arXiv2020

Strong decays of fully-charm tetraquarks into di-charmonia

We study strong decays of the possible fully-charm tetraquarks recently observed by LHCb, and calculate their relative branching ratios through the Fierz rearrangement. Together with our previous QCD sum rule study [Phys. Lett. B 773, 247 (2017)], our results suggest that the broad structure around $6.2$-$6.8$ GeV can be interpreted as an $S$-wave $cc\bar c \bar c$ tetraquark state with $J^{PC} = 0^{++}$ or $2^{++}$, and the narrow structure around 6.9 GeV can be interpreted as a $P$-wave one with $J^{PC} = 0^{-+}$ or $1^{-+}$. These structures were observed in the di-$J/ψ$ invariant mass spectrum, and we propose to confirm them in the di-$η_c$, $J/ψh_c$, $η_c χ_{c0}$, and $η_c χ_{c1}$ channels. We also propose to search for their partner states having the negative charge-conjugation parity in the $J/ψη_c$, $J/ψχ_{c0}$, $J/ψχ_{c1}$, and $η_c h_c$ channels.

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arXiv2020

QCD sum rule studies on the $s s \bar s \bar s$ tetraquark states of $J^{PC} = 0^{-+}$

We apply the method of QCD sum rules to study the $s s \bar s \bar s$ tetraquark states of $J^{PC} = 0^{-+}$. We construct all the relevant $s s \bar s \bar s$ tetraquark currents, and find that there are only two independent ones. We use them to further construct two weakly-correlated mixed currents. One of them leads to reliable QCD sum rule results and the mass is extracted to be $2.51^{+0.15}_{-0.12}$ GeV, suggesting that the $X(2370)$ or the $X(2500)$ can be explained as the $ss\bar s\bar s$ tetraquark state of $J^{PC} = 0^{-+}$. To verify this interpretation, we propose to further study the $ππ/K \bar K$ invariant mass spectra of the $J/ψ\to γππη^\prime/γK \bar K η^\prime$ decays in BESIII to examine whether there exists the $f_0(980)$ resonance.

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arXiv2020

Decay properties of the $Z_c(3900)$ through the Fierz rearrangement

We systematically construct all the tetraquark currents/operators of $J^{PC} = 1^{+-}$ with the quark configurations $[cq][\bar c \bar q]$, $[\bar c q][\bar q c]$, and $[\bar c c][\bar q q]$ ($q=u/d$), and derive their relations through the Fierz rearrangement of the Dirac and color indices. Using the transformations of $[qc][\bar q \bar c] \to [\bar c c][\bar q q]$ and $[\bar c q][\bar q c]$, we study decay properties of the $Z_c(3900)$ as a compact tetraquark state; while using the transformation of $[\bar c q][\bar q c] \to [\bar c c][\bar q q]$, we study its decay properties as a hadronic molecular state.

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arXiv2020

Identifying the $Λ_b(6146)^0$ and $Λ_b(6152)^0$ as $D$-wave bottom baryons

We study the $Λ_b(6146)^0$ and $Λ_b(6152)^0$ recently observed by LHCb using the method of QCD sum rules within the framework of heavy quark effective theory. Our results suggest that they can be interpreted as $D$-wave bottom baryons of $J^P = 3/2^+$ and $5/2^+$ respectively, both of which contain two $λ$-mode excitations. We also investigate other possible assignments containing $ρ$-mode excitations. We predict masses of their strangeness partners to be $m_{Ξ_b(3/2^+)} = 6.26^{+0.11}_{-0.14}$ GeV and $m_{Ξ_b(5/2^+)} = 6.26^{+0.11}_{-0.14}$ GeV with the mass splitting $ΔM = 4.5^{+1.9}_{-1.5}$ MeV, and propose to search for them in future LHCb and CMS experiments.

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arXiv2020

Is the $X17$ composed of four bare quarks?

When studying tetraquark states using the method of QCD sum rules, we find some tetraquark currents, such as $\bar u_L γ_μd_L~\bar d_L γ^μu_L$ and $\bar u_L γ_μd_L~\bar d_R γ^μu_R$, etc. We calculate their correlation functions using the method of operator product expansion, and find that non-perturbative QCD effects do not contribute much to them. This indicates the possible existence of tetraquark states composed of bare quarks with abnormally small masses. We study the possible assignment of the $X17$ as such a state. We argue that the Atomki experiments might observe a new type of nuclear decay process, where sea quarks take away the extra energy of the nucleus. A unique feature of this tetraquark assignment is that we predict two almost degenerate states with significantly different widths.

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arXiv2020

Excited $Ω_b$ baryons and fine structure of strong interaction

The heavy baryon system bounded by the strong interaction has a rich internal structure, so its mass spectra can have the fine structure similar to the line spectra of atom bounded by the electromagnetic interaction. We systematically study the internal structure of $P$-wave $Ω_b$ baryons and calculate their $D$-wave decay properties. The present study, together with our previous studies on their mass spectra and $S$-wave decay properties, suggest that all the four excited $Ω_b$ baryons recently discovered by LHCb can be well explained as $P$-wave $Ω_b$ baryons, and their beautiful fine structure is directly related to the rich internal structure of $P$-wave $Ω_b$ baryons.

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arXiv2020

Decay properties of $P$-wave heavy baryons accompanied by vector mesons within light-cone sum rules

We use the method of light-cone sum rules to study decay properties of $P$-wave bottom baryons belonging to the $SU(3)$ flavor $\mathbf{6}_F$ representation. In Ref.~\cite{Cui:2019dzj} we have studied their mass spectrum and pionic decays, and found that the $Σ_{b}(6097)$ and $Ξ_{b}(6227)$ can be well interpreted as $P$-wave bottom baryons of $J^P = 3/2^-$. In this paper we further study their decays into ground-state bottom baryons and vector mesons. We propose to search for a new state $Ξ_b({5/2}^-)$, that is the $J^P = 5/2^-$ partner state of the $Ξ_{b}(6227)$, in the $Ξ_b({5/2}^-) \to Ξ_b^{*}ρ\to Ξ_b^{*}ππ$ decay process. Its mass is $12 \pm 5$~MeV larger than that of the $Ξ_{b}(6227)$.

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arXiv2019

Possible interpretations of the $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$

Based on our previous QCD sum rule studies on hidden-charm pentaquark states, we discuss possible interpretations of the $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$, which were recently observed by LHCb. Our results suggest that the $P_c(4312)$ can be well interpreted as the $[Σ_c^{++} \bar D^-]$ bound state with $J^P = 1/2^-$, while the $P_c(4440)$ and $P_c(4457)$ can be interpreted as the $[Σ_c^{+} \bar D^0]$ bound state with $J^P = 1/2^-$, the $[Σ_c^{*++} \bar D^{-}]$ and $[Σ_c^{+} \bar D^{*0}]$ bound states with $J^P = 3/2^-$, or the $[Σ_c^{*+} \bar D^{*0}]$ bound state with $J^P = 5/2^-$. We propose to measure their spin-parity quantum numbers to verify these assignments.

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arXiv2019

Exotic $ΩΩ$ dibaryon states in a molecular picture

We investigate the exotic $ΩΩ$ dibaryon states with $J^P=0^+$ and $2^+$ in a molecular picture. We construct the scalar and tensor $Ω$$Ω$ molecular interpolating currents and calculate their masses within the method of QCD sum rules. Our results indicate that the mass of the scalar dibaryon state is $m_{ΩΩ, \, 0^+}=(3.33\pm0.22) \,\unit$, which is about $15 \,\mathrm{MeV}$ below the $2m_Ω$ threshold. This result suggests the existence of a loosely bound molecular state of the $J^P=0^+$ scalar $ΩΩ$ dibaryon with a small binding energy around 15 MeV. The mass of the tensor dibaryon is predicted to be $m_{ΩΩ,\, 2^+}=(3.24\pm0.23)\, \mbox{GeV}$, which may imply a deeper molecular state of the tensor $ΩΩ$ dibaryon than the scalar channel. These exotic strangeness $S=-6$ and doubly-charged $ΩΩ$ dibaryon states may be identified in the heavy-ion collision processes.

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arXiv2019

Identifying the $Ξ_{b}(6227)$ and $Σ_{b}(6097)$ as $P$-wave bottom baryons of $J^P = 3/2^-$

We use the method of QCD sum rules within the framework of heavy quark effective theory to study the mass spectrum of the $Σ_{b}(6097)^{\pm}$ and $Ξ_{b}(6227)^{-}$, and use the method of light-cone sum rules still within the heavy quark effective theory to study their decay properties. Our results suggest that they can be well interpreted as $P$-wave bottom baryons with the spin-parity $J^P = 3/2^-$. They belong to the baryon doublet $[\mathbf{6}_F, 2, 1, λ]$, where the total and spin angular momenta of the light degree of freedom are $j_l = 2$ and $s_l = 1$, and the orbital angular momentum is between the bottom quark and the two-light-quark system ($λ$-type). This doublet contains six bottom baryons, and we predict masses (mass differences) and decay widths of the other four states to be $M_{Ω_b(3/2^-)} = 6.46 \pm 0.12 {~\rm GeV}$, $Γ_{Ω_b(3/2^-)} = 58{^{+65}_{-33}} {~\rm MeV}$, $M_{Σ_b(5/2^-)}-M_{Σ_b(3/2^-)}= 13 \pm 5 {~\rm MeV}$, $M_{Ξ_b^{\prime}(5/2^-)}-M_{Ξ_b^{\prime}(3/2^-)} = 12 \pm 5 {~\rm MeV}$, and $M_{Ω_b(5/2^-)}-M_{Ω_b(3/2^-)} = 11 \pm 5 {~\rm MeV}$. We propose to search for them in further LHCb experiments.

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arXiv2019

Triangle singularity in the $J/ψ\rightarrow K^+ K^- f_0(980)(a_0(980))$ decays

We study the $J/ψ\rightarrow K^+ K^- f_0(980)(a_0(980))$ reaction and find that the mechanism to produce this decay develops a triangle singularity around $M_{\rm inv}(K^- f_0/K^- a_0) \approx 1515$~MeV. The differential width $dΓ/ dM_{\rm inv}(K^- f_0/K^- a_0)$ shows a rapid growth around the invariant mass being 1515~MeV as a consequence of the triangle singularity of this mechanism, which is directly tied to the nature of the $f_0(980)$ and $a_0(980)$ as dynamically generated resonances from the interaction of pseudoscalar mesons. The branching ratios obtained for the $J/ψ\rightarrow K^+ K^- f_0(980)(a_0(980))$ decays are of the order of $10^{-5}$, accessible in present facilities, and we argue that their observation should provide relevant information concerning the nature of the low-lying scalar mesons.

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arXiv2019

Pentaquark and Tetraquark states

The past seventeen years have witnessed tremendous progress on the experimental and theoretical explorations of the multiquark states. The hidden-charm and hidden-bottom multiquark systems were reviewed extensively in [Phys. Rept. 639 (2016) 1-121]. In this article, we shall update the experimental and theoretical efforts on the hidden heavy flavor multiquark systems in the past three years. Especially the LHCb collaboration not only confirmed the existence of the hidden-charm pentaquarks but also provided strong evidence of the molecular picture. Besides the well-known $XYZ$ and $P_c$ states, we shall discuss more interesting tetraquark and pentaquark systems either with one, two, three or even four heavy quarks. Some very intriguing states include the fully heavy exotic tetraquark states $QQ\bar Q\bar Q$ and doubly heavy tetraquark states $QQ\bar q \bar q$, where $Q$ is a heavy quark. The $QQ\bar Q\bar Q$ states may be produced at LHC while the $QQ\bar q \bar q$ system may be searched for at BelleII and LHCb. Moreover, we shall pay special attention to various theoretical schemes. We shall emphasize the model-independent predictions of various models which are truly/closely related to Quantum Chromodynamics (QCD). There have also accumulated many lattice QCD simulations through multiple channel scattering on the lattice in recent years, which provide deep insights into the underlying structure/dynamics of the $XYZ$ states. In terms of the recent $P_c$ states, the lattice simulations of the charmed baryon and anti-charmed meson scattering are badly needed. We shall also discuss some important states which may be searched for at BESIII, BelleII and LHCb in the coming years.

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arXiv2019

Revisiting hidden-charm pentaquarks from QCD sum rules

We revisit the hidden-charm pentaquark states $P_c(4380)$ and $P_c(4450)$ using the method of QCD sum rules by requiring the pole contribution to be larger than or around 30\% to better insure the one-pole parametrization to be valid. We find two mixing currents and our results suggest that the $P_c(4380)$ and $P_c(4450)$ can be identified as hidden-charm pentaquark states having $J^P=3/2^-$ and $5/2^+$, respectively, while there still exist other possible spin-parity assignments, such as $J^P=3/2^+$ and $J^P=5/2^-$, which needs to be clarified in further theoretical and experimental studies.

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arXiv2019

Settling the $Z_c(4600)$ in the charged charmonium-like family

Very recently LHCb reported the evidence of a new charged charmonium-like structure in the $J/ψπ^-$ invariant mass spectrum near 4600 MeV. In this work we investigate this structure together with three other charged charmonium-like states, the $Z_c(3900)$, $Z_c(4020)$, and $Z_c(4430)$. Our results suggest that the two higher states can be established as the first radial excitations of the two lower ones, all of which have the quantum numbers $J^{PC}=1^{+-}$. We propose to search for more relationship among exotic hadrons in order to better understand them.

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arXiv2019

QCD sum rule studies on the $s s \bar s \bar s$ tetraquark states with $J^{PC} = 1^{+-}$

We apply the method of QCD sum rules to study the structure $X$ newly observed by the BESIII Collaboration in the $ϕη^\prime$ mass spectrum in 2.0-2.1 GeV region in the $J/ψ\rightarrow ϕηη^\prime$ decay. We construct all the $s s \bar s \bar s$ tetraquark currents with $J^{PC} = 1^{+-}$, and use them to perform QCD sum rule analyses. One current leads to reliable QCD sum rule results and the mass is extracted to be $2.00^{+0.10}_{-0.09}$ GeV, suggesting that the structure $X$ can be interpreted as an $s s \bar s \bar s$ tetraquark state with $J^{PC} = 1^{+-}$. The $Y(2175)$ can be interpreted as its $s s \bar s \bar s$ partner having $J^{PC} = 1^{--}$, and we propose to search for the other two partners, the $s s \bar s \bar s$ tetraquark states with $J^{PC} = 1^{++}$ and $1^{-+}$, in the $η^\prime f_0(980)$, $η^\prime K \bar K$, and $η^\prime K \bar K^*$ mass spectra.

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arXiv2018

Baryon fields with $U_{L}(3)\times U_{R}(3)$ chiral symmetry V: Pion-Nucleon and Kaon-Nucleon $Σ$ Terms

We have previously calculated the pion-nucleon $Σ_{πN}$ term in the chiral mixing approach with $u,d$ flavors only, and found the lower bound $Σ_{πN} \geq \left(1 + \frac{16}{3} \sin^2 θ\right){3 \over 2} \left(m_{u}^{0} + m_{d}^{0}\right)$. The mixing angle $θ$ can be calculated as $\sin^2θ= \frac{3}{8}\left(g_A^{(0)} + g_A^{(3)}\right)$. With presently accepted values of current quark masses, this leads to $Σ_{πN} \geq 58.0 \pm 4.5 \begin{array}{l} +11.4 \\ -6.5 \end{array}$ MeV, which is in agreement with the values extracted from experiments, and substantially higher than most previous two-flavour calculations. The causes of this enhancement are: 1) the large, ($\frac{16}{3}\simeq 5.3$), purely $SU_L(2) \times SU_R(2)$ algebraic factor, 2) the admixture of the $[(\mathbf{1},\mathbf{\frac12})\oplus (\mathbf{\frac12},\mathbf{1})]$ chiral multiplet component in the nucleon, whose presence has been known for some time, but that had not been properly taken into account, yet. We have now extended these calculations of $Σ_{πN}$ to three light flavours, i.e., to $SU_L(3) \times SU_R(3)$ multiplet mixing. Phenomenology of chiral $SU_L(3) \times SU_R(3)$ multiplet mixing demands the presence of three chiral $SU_L(3) \times SU_R(3)$ multiplets in order to successfully reproduce the baryons' flavor-octet and flavor-singlet axial currents, as well as the baryon anomalous magnetic moments. The physical significance of these results lies in the fact that they show no need for $q^4 {\bar q}$ components, and in particular, no need for an $s \bar s$ component in the nucleon, in order to explain the large "observed" $Σ_{πN}$ value. We also predict the experimentally unknown kaon-nucleon sigma term $Σ_{K N}$.

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