arXiv subjects

Hua-Xing Chen

Publications and source records attributed to Hua-Xing Chen.

At least 37 records · Page 2Linked to original sources

arXiv2025

$T_{bc\bar s}$ states in the process $Υ\to D^{-} \bar B^{0} D_s^{+}$

We perform a theoretical study of the decay process $Υ\to D^{-} \bar{B}^{0} D_s^{+}$ in search of the doubly heavy tetraquark states $T_{bc\bar{s}}$ with quark content $bc\bar{s}\bar{d}$. These $T_{bc\bar{s}}$ states are assumed to be dynamically generated molecular states from the S-wave interactions between $\bar{B}_s^{(*)0} D^{(*)+}$ and $\bar{B}^{(*)0} D_s^{(*)+}$ meson pairs. Based on the total angular momentum and the type of the constituent mesons (pseudoscalars $P$ or vectors $V$), they are labeled as $T_{bc\bar{s}}^{0, PP}$, $T_{bc\bar{s}}^{0, VV}$, and $T_{bc\bar{s}}^{2, VV}$, respectively. The $\bar{B}^{0} D_s^{+}$ invariant mass distribution for this decay is calculated using current algebra, incorporating contributions from $T_{bc\bar{s}}$ states arising from final-state interactions. Our results reveal a clear peak structure in the $7415 - 7425$ MeV region, which is attributed to the $T_{bc\bar{s}}^{2, VV}$ state. Additionally, a distinct dip structure appears near the $\bar{B}^{*0} D_s^{*+}$ threshold, characteristic of the $T_{bc\bar{s}}^{2, VV}$ as a hadronic molecular state. A near-threshold enhancement associated with the $T_{bc\bar{s}}^{0, PP}$ state and a dip arising from the $T_{bc\bar{s}}^{0,\,VV}$ state are also identified, though the manifestation of these features depends sensitively on model parameter fine-tuning. Therefore, with increased experimental statistics, the decay channel $Υ\to D^{-} \bar{B}^{0} D_s^{+}$ offers a promising avenue for discovering and characterizing the $T_{bc\bar{s}}$ states.

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arXiv2025

Topped baryons from QCD sum rules

The recent CMS observation of a near-threshold enhancement in top quark pair production provides the first experimental indication of a short-lived pseudoscalar $t\bar{t}$ bound state, commonly referred to as toponium. While most existing studies focus on toponium using perturbative QCD near threshold, baryonic configurations containing a single top quark -- singly topped baryons -- offer a complementary nonperturbative perspective. Notably, singly topped baryons are expected to exhibit a longer lifetime and a narrower decay width than toponium, since only one top quark decays rather than two. The heavy quark effective theory provides a natural and powerful framework for analyzing such systems, allowing the separation of heavy and light quark dynamics. In this work we employ heavy quark effective theory to investigate the internal structure of ground-state singly topped baryons. We construct their interpolating currents and analyze them using QCD sum rules. The resulting masses of the ground-state singly topped baryons are found to lie around 174 GeV, approximately $1.1$-$1.5$ GeV above the pole mass of the top quark.

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arXiv2025

Light hybrid baryons in QCD sum rules

We have calculated the mass spectra of nucleon and delta hybrid baryons with both positive-parity and negative-parity by using the method of QCD sum rules. We predicte that the lowest-lying hybrid baryons are the negative-parity $N_{1/2^-}$ and $Δ_{1/2^-}$ states, while the positive-parity ones are much heavier. We suggest to search for these light hybrid baryons via the $χ_{cJ}/Υ$ decay processes in the future.

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arXiv2025

A hybrid nonet with $J^{PC}=1^{-+}$ or a tetraquark 81-plet

Confirming the existence of hybrid states remains challenging due to their experimental indistinguishability from tightly bound tetraquarks and loosely bound molecules. To address this issue, we employ QCD sum rules to systematically investigate the $π_1(1600)$ and $η_1(1855)$ as candidate tetraquark states with exotic quantum numbers $J^{PC} = 1^{-+}$. Within the hybrid framework, an $SU(3)$ flavor nonet is expected, featuring two isoscalar configurations, $q\bar{q}g$ and $s\bar{s}g$, where $q = u/d$. In contrast, the tetraquark scenario predicts an $SU(3)$ flavor 81-plet comprising three isoscalar states: $qq\bar{q}\bar{q}$, $qs\bar{q}\bar{s}$, and $ss\bar{s}\bar{s}$. Our analysis yields a mass of $2.22^{+0.18}_{-0.26}$ GeV for the $ss\bar{s}\bar{s}$ tetraquark state, which is expected to decay predominantly into the $ϕϕ$ and $ηf_1(1420)$ final states. Therefore, experimental scrutiny of their invariant mass spectra is pivotal for distinguishing between hybrid and tetraquark interpretations.

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arXiv2025

Radiative decays of $P$-wave charmed baryons in the $SU(3)$ flavor $\bf6_F$ representation

We perform a comprehensive investigation of the radiative decays of $P$-wave charmed baryons in the $SU(3)$ flavor $\mathbf{6}_F$ representation, employing the light-cone QCD sum rule approach within the framework of heavy quark effective theory. We analyze their electromagnetic transitions into ground-state charmed baryons via photon emission. When combined with the mass spectra and strong decay properties previously studied in Ref.~\cite{Yang:2021lce}, our results constitute a systematic and complete QCD sum rule analysis of the $P$-wave singly charmed baryons within the framework of heavy quark effective theory. As summarized in Table~\ref{tab:result}, several excited charmed baryons are found to possess suppressed strong decay widths, thereby rendering their radiative decay channels particularly significant for experimental identification and theoretical understanding.

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arXiv2025

Fully-heavy hadronic molecules $B_c^{()+} B_c^{()-}$ bound by fully-heavy mesons

A lot of exotic hadrons were reported in the past twenty years, which bring us the renaissance of the hadron spectroscopy. Most of them can be understood as hadronic molecules, whose interactions are mainly due to the exchange of light mesons, and specifically, light vector mesons through the coupled-channel unitary approach within the local hidden-gauge formalism. It is still controversial whether the interaction arising from the exchange of heavy mesons is capable of forming hadronic molecules. We apply the coupled-channel unitary approach to study the fully-heavy $b \bar b c \bar c$ system, where the exchanged mesons can only be the fully-heavy vector mesons $J/ψ$, $B_c^*$, and $Υ$. Especially, the $J/ψ$ meson is much lighter than the $B_c^{(*)}$ mesons, so the present study can be taken as a general investigation on the question whether a lower-mass fully-heavy meson is able to bind two higher-mass fully-heavy hadrons. Our results suggest the existence of the fully-heavy hadronic molecules $|B_c^{+} B_c^{-}; J^{PC}=0^{++} \rangle$, $|B_c^{*+} B_c^{-} - c.c.; J^{PC}=1^{+-} \rangle$, and $|B_c^{*+} B_c^{*-}; J^{PC}=2^{++} \rangle$ as well as the possible existence of $|B_c^{*+} B_c^{-} + c.c.; J^{PC}=1^{++} \rangle$. These states are potentially to be observed in the $μ^+ μ^- J/ψ$ and $μ^+ μ^- Υ$ channels in future ATLAS, CMS, and LHCb experiments.

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arXiv2025

$P$-wave single charmed baryons of the $SU(3)$ flavor $\bf\bar3_F$

We study the $P$-wave single charmed baryons of the $SU(3)$ flavor $\bf\bar3_F$ within the framework of heavy quark effective theory. We systematically calculate their strong and radiative decay properties using the light-cone sum rule method. Besides the $Λ_c(2595)$, $Λ_c(2625)$, $Ξ_c(2790)$, and $Ξ_c(2815)$, our results suggest the existence of two additional $Λ_c$ baryons and two additional $Ξ_c$ baryons. Their masses, mass splittings within the same multiplets, and decay properties are summarized in Table V for future experimental searches.

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arXiv2025

Strong decay properties of P-wave single bottom baryons of the SU(3) flavor antitriplet $\bf\bar 3_F$

We study the $P$-wave bottom baryons of the $SU(3)$ flavor antitriplet and systematically calculate their strong decay properties, including their $D$-wave decays into ground-state bottom baryons with light pseudoscalar mesons and $S$-wave decays into ground-state bottom baryons with light vector mesons. Together with Refs.~\cite{Tan:2023opd,Yang:2019cvw,Yang:2020zrh,Luo:2024jov}, a rather complete investigation has been performed to study their mass spectra and strong/radiative decay properties, through the methods of QCD sum rules and light-cone sum rules within the framework of heavy quark effective theory. Among various possibilities, we identify four $Λ_b$ and four $Ξ_b$ baryons, with limited decay widths and so capable of being observed in experiments. Their masses, mass splittings within the same multiplets, and strong/radiative decay widths are summarized in Table~\ref{tab:decayb3f} for future experimental searching.

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arXiv2025

Radiative decays of $P$-wave bottom baryons from light-cone sum rules

We carry out a comprehensive investigation on the radiative decays of $P$-wave bottom baryons using the light-cone sum rule method. We analyze their electromagnetic transitions into ground-state bottom baryons together with a photon. Together with their mass spectra and strong decays investigated in Refs. \cite{Yang:2020zrh,Tan:2023opd}, a rather complete QCD sum rule study has been done to understand the $P$-wave singly bottom baryons within the framework of heavy quark effective theory. As summarized in Tables~\ref{tab:candidate}/\ref{tab:candidate6f}, some $P$-wave bottom baryons have limited strong decay widths so that their radiative decay widths become non-negligible. We propose to study these excited bottom baryons and their radiative decays in the future Belle-II, BESIII, and LHCb experiments.

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arXiv2025

Hadronic molecules with four charm or beauty quarks

We apply the extended local hidden gauge formalism to study the meson-meson interactions with the quark constituents $cc\bar c\bar c$, $cc\bar c\bar b/\bar c\bar c cb$, $cc\bar b\bar b/\bar c\bar c bb$, $bb\bar c\bar b/\bar b\bar b cb$, and $bb\bar b\bar b$, where the exchanged mesons are the fully-heavy vector mesons $J/ψ$, $B_c^*$, and $Υ$. We solve the coupled-channel Bethe-Salpeter equation to derive two poles in the $bb\bar{c}\bar{b}$ system and two poles in the $cc\bar{c}\bar{b}$ system. There are also four charge-conjugated poles in the $\bar{b}\bar{b}cb$ and $\bar{c}\bar{c}cb$ systems. In the $bb\bar{c}\bar{b}$ system, one pole corresponds to a sub-threshold bound state when the cutoff momentum is set to $Λ> 850$ MeV. The other pole in this system corresponds to a sub-threshold bound state when $Λ> 1100$ MeV. In the $cc\bar{c}\bar{b}$ system, the two poles correspond to sub-threshold bound states only when $Λ> 1550$ MeV and $Λ> 2650$ MeV. This makes them difficult to identify as deeply-bound hadronic molecules. We propose investigating the two poles of the $bb\bar{c}\bar{b}$ system in the $ μ^+μ^-B_c^-$channel at the LHC.

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arXiv2024

Charmonium-like states with the exotic quantum number $J^{PC} = 3^{-+}$

We apply the method of QCD sum rules to study the $q c \bar q \bar c$ tetraquark states with the exotic quantum number $J^{PC} = 3^{-+}$, and extract the mass of the lowest-lying state to be ${4.49^{+0.45}_{-0.41}}$ GeV. To construct the relevant tetraquark currents we need to explicitly add the covariant derivative operator. Our systematic analysis of these interpolating currents indicates that: a) this state readily decays into the $P$-wave $[ρJ/ψ] / [ωJ/ψ]$ channel but not into the $ [ρχ_{c2}]/[ωχ_{c2}]/[J/ψf_2(1270)]$ channels, and b) it readily decays into the $[D^* \bar D_2^*]$ channel but not into the $P$-wave $[D^* \bar D^*]$ channel.

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arXiv2024

Towards heavy double-gluon hybrid mesons with exotic quantum numbers in QCD sum rules

The double-gluon hybrid meson configuration was recently proposed and investigated within QCD sum rules. In this talk, we discuss the color structures of the double-gluon hybrid meson and construct current operators with exotic quantum numbers $J^{PC}=1^{-+}$ and $2^{+-}$ for two of the structures. In the framework of QCD sum rules, we consider the condensates up to dimension-8 at the leading order of $α_{s}$ for both charmonium and the bottomonium systems. The results indicate that the masses of the $1^{-+}$ and $2^{+-}$ charmonium double-gluon hybrid mesons are approximately $6.1-7.2$ GeV and $6.3-6.4$ GeV, respectively. As for the bottomonium systems, their masses fall within the range of $13.7-14.3$ GeV and $12.6-13.3$ GeV for the $1^{-+}$ and $2^{+-}$ channels, respectively. Additionally, the charmonium hybrids could be produced in the radiative decays of bottomonium mesons in BelleII experiment.

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arXiv2024

Investigation on the $Ω(2012)$ from QCD sum rules

We investigate the recently observed $Ω(2012)$ baryon using QCD sum rules. By constructing $P$-wave $Ω$ baryon currents and performing spin projection and parity projection, we obtain the masses of the $J^P = 1/2^-$ and $3/2^-$ states as $M_{1/2^-} = 2.07^{+0.07}_{-0.07}{\rm~GeV}$ and $M_{3/2^-} = 2.05^{+0.09}_{-0.10}{\rm~GeV}$ in good agreement with experiment. This suggests that $Ω(2012)$ is likely to be a negative parity $P$-wave excited state, though its spin remains undetermined and requires further study of its decay properties.

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arXiv2024

Light single-gluon hybrid states with various (exotic) quantum numbers

We apply the QCD sum rule method to study the light single-gluon hybrid states with various (exotic) quantum numbers. We construct twenty-four single-gluon hybrid currents, and use eighteen of them to calculate the masses of forty-four single-gluon hybrid states with the quark-gluon contents $\bar q q g$ ($q=u/d$) and $\bar s s g$. We concentrate on the hybrid states with the exotic quantum number $J^{PC} = 1^{-+}$, whose masses and widths are calculated to be $M_{|\bar q q g;1^-1^{-+}\rangle} =1.67^{+0.15}_{-0.17}$ GeV, $Γ_{|\bar q q g;1^-1^{-+}\rangle} = 530^{+540}_{-330}$ MeV, $M_{|\bar q q g;0^+1^{-+}\rangle} = 1.67^{+0.15}_{-0.17}$ GeV, $Γ_{|\bar q q g;0^+1^{-+}\rangle} = 120^{+160}_{-110}$ MeV, $M_{|\bar s s g;0^+1^{-+}\rangle} = 1.84^{+0.14}_{-0.15}$ GeV, and $Γ_{|\bar s s g;0^+1^{-+}\rangle} = 100^{+110}_{-~80}$ MeV. Our results support the interpretations of the $π_1(1600)$ and $η_1(1855)$ as the hybrid states $|\bar q q g;1^-1^{-+}\rangle$ and $|\bar s s g;0^+1^{-+}\rangle$, respectively. Considering the uncertainties, our results suggest that the $π_1(1600)$ and $η_1(1855)$ may also be interpreted as the hybrid states $|\bar q q g;1^-1^{-+}\rangle$ and $|\bar q q g;0^+1^{-+}\rangle$, respectively. To differentiate these two assignments and to verify whether they are hybrid states or not, we propose to examine the $a_1(1260) π$ decay channel in future experiments.

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arXiv2024

Investigation on the $Ω(2012)$ from QCD sum rules

We study the recently observed $Ω(2012)$ baryon in QCD sum rules. We construct the $P$-wave $Ω$ baryon currents with a covariant derivative, and perform spin projection to obtain the currents with total spin 1/2 and 3/2. We then apply the parity-projected QCD sum rules to separate the contributions of the positive and negative parity states. We extract the masses of $J^P = 1/2^-$ and $3/2^-$ states to be $M_{1/2^-} = 2.07^{+0.07}_{-0.07}{\rm~GeV}$ and $M_{3/2^-} = 2.05^{+0.09}_{-0.10}{\rm~GeV}$. Both results are in good agreement with the experimental result. Therefore, it is likely that the $Ω(2012)$ is a negative parity state, which is interpreted as a $P$-wave excited state in the quark model. However, its spin is not determined in the present analysis, which can be done by detailed study on its decay properties.

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arXiv2024

Revisit the heavy quarkonium double-gluon hybrid mesons with exotic quantum numbers

We revisit the masses of heavy quarkonium double-gluon hybrid mesons with exotic quantum numbers $J^{PC}=1^{-+}$ and $2^{+-}$ in the framework of the QCD sum rules. Considering the double-gluon hybrid meson operators in the octet-octet color structure, we have constructed two independent interpolating currents with $J^{PC}=1^{-+}$ and five independent currents with $J^{PC}=2^{+-}$. For the interpolating currents with antisymmetric glueball operator, there exist non-local divergences in one kind of additional Feynman diagrams of the tri-gluon condensate, which will give important contributions to the sum rule stabilities and mass predictions. We use the diagrammatic renormalization to cancel out such divergences. At the leading order of $α_s$, the two-point correlation functions and spectral densities can be expressed in the analytic form of the generalized hypergeometric functions and Meijer's G-functions. After performing the numerical analysis, we predict the masses of the $1^{-+}$ and $2^{+-}$ charmonium double-gluon hybrid mesons to be around $6.1-7.2$ GeV and $6.3-6.4$ GeV, respectively. For the bottomonium systems, their masses are predicted to be $13.7-14.3$ GeV and $12.6-13.3$ GeV for the $1^{-+}$ and $2^{+-}$ channels, respectively. Besides, it is possible to hunt for these charmonium hybrids in the radiative decays of bottomonium mesons in BelleII experiment. Further investigations on these hybrid states in various theoretical and phenomenological methods are also anticipated in the future.

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arXiv2024

$\bar{B}_s^0 \to D_{s1}(2460)^+ K^-, D_{s1}(2536)^+ K^-$ and the nature of the two $D_{s1}$ resonance

Starting from the molecular picture for the $D_{s1}(2460)$ and $D_{s1}(2536)$ resonances, which are dynamically generated by the interaction of coupled channels, the most important of which are the $D^*K$ for the $D_{s1}(2460)$ and $DK^*$ for the $D_{s1}(2536)$, we evaluate the ratio of decay widths for the $\bar{B}_s^0 \to D_{s1}(2460)^+ K^-$ and $\bar{B}_s^0 \to D_{s1}(2536)^+ K^-$ decays, the latter of which has been recently investigated by the LHCb collaboration, and we obtain a ratio of the order of unity. The present results should provide an incentive for the related decay into the $D_{s1}(2460)$ resonance to be performed, which would provide valuable information on the nature of these two resonances.

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arXiv2024

QCD sum rule studies on the possible double-peak structure of the $X17$ particle

The $X17$ particle, discovered by Krasznahorkay et al. at ATOMKI, was recently confirmed in the $γγ$ invariant mass spectra by Abraamyan et al. at JINR. We notice with surprise and interest that the $X17$ seems to have a double-peak structure. This is in a possible coincidence with our QCD sum rule study of [arXiv:2006.01018], where we interpreted the $X17$ as a tetraquark state composed of four bare quarks ($u \bar u d \bar d$), and claimed that ``A unique feature of this tetraquark assignment is that we predict two almost degenerate states with significantly different widths''. These two different tetraquark states are described by two different chiral tetraquark currents $\bar u_L γ_μd_L~\bar d_L γ^μu_L$ and $\bar u_L γ_μd_L~\bar d_R γ^μu_R$. To verify whether the tetraquark assignment is correct or not, we replace the up and down quarks by the strange quarks, and apply the QCD sum rule method to study the other four chiral tetraquark currents $\bar u_L γ_μs_L~\bar s_L γ^μu_L$, $\bar u_L γ_μs_L~\bar s_R γ^μu_R$, $\bar d_L γ_μs_L~\bar s_L γ^μd_L$, and $\bar d_L γ_μs_L~\bar s_R γ^μd_R$. We calculate their correlation functions, and find that non-perturbative QCD effects do not contribute much to them. Our results suggest that there may exist four almost degenerate tetraquark states with masses about $236\sim296$ MeV. Each of these states is composed of four bare quarks, either $u \bar u s \bar s$ or $d \bar d s \bar s$.

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