arXiv subjects

Bo-Chao Liu

Publications and source records attributed to Bo-Chao Liu.

At least 19 recordsLinked to original sources

arXiv2026

Hyperon-Nucleon Spectrometer

Chirality lies at the heart of low-energy QCD, governing the symmetry structure that shapes hadron masses and strong interaction dynamics. Among the most compelling open questions tied to chiral dynamics and spontaneous chiral symmetry breaking is the longstanding $Λ$ polarization puzzle, in which $Λ$ hyperons produced in unpolarized hadronic collisions exhibit a surprisingly large transverse polarization that remains theoretically unexplained. This whitepaper presents the proposal for the Hyperon-Nucleon Spectrometer (H-NS) at the High-Intensity heavy-ion Accelerator Facility (HIAF). Leveraging the high energy and high intensity of HIAF's proton and heavy-ion beams, the H-NS experiment will perform systematic studies of hyperon polarization phenomena and their underlying mechanisms in proton-proton ($pp$), proton-nucleus ($pA$), and nucleus-nucleus ($AA$) collisions in the fixed target mode. A wide-range beam energy scan, including proton beams from 3 GeV up to 9.3 GeV (HIAF) and up to 32 GeV (upgraded HIAF), will be conducted to examine the dependence of polarization on collision energy. The spectrometer is designed with specialized detectors capable of high-precision reconstruction of final-state baryon polarizations. Among its many interesting and important measurements, H-NS will simultaneously measure hyperon and proton spin observables to explore the polarization mechanism in hadronic interactions and the spin structure of baryons. Furthermore, the use of $pA$ and $AA$ collisions will enable detailed investigations of cold and hot nuclear matter effects on spin polarization. Its physics program and detector development will significantly benefit the future Electron-ion Collider in China.

physics.ins-det↗

arXiv2025

Roles of $Λ$ resonances in the $K^- p \to γΣ$ reaction

We investigate the $K^- p \to γΣ$ reaction using an effective Lagrangian approach within an isobar model framework. The model includes contributions from $s$-channel hyperon and hyperon resonance, $t$-channel $K$ and $K^*$, $u$-channel proton and $Δ(1232)$ exchanges, and a phenomenological contact term. Our analysis focuses on the roles of various $Λ$ resonances. The results indicate that the $Λ(1600)$ resonance is crucial for describing the experimental data at lower energies. At higher energies, the inclusion of either the $Λ(1670)$ or the $Λ(1690)$ resonance significantly improves the agreement with data. However, the current data are insufficient to distinguish between these two scenarios. We suggest that future measurements at higher beam energies and the measurement of the $Σ$ polarization are needed to identify the roles of the $Λ(1670)$ and $Λ(1690)$ resonances.

hep-ph↗

arXiv2025

Sifting out the neutral and charged components of $X(3872)$ from a spin observable

In this work, we propose a new method to detect the composition of the $X(3872)$ state. Based on a widely accepted interpretation that $X(3872)$ is a weakly bound $S$-wave molecule of the $D^{*0} \bar{D}^{0}$ (neutral) and $D^{*+} D^{-}$ (charged) configurations, the process $X(3872) \to \bar{D}^{*0} D^0$ is described by one-loop triangle diagrams with the corresponding components as intermediate particles, and with the parameters constrained by the experimental branching ratio. Unlike the mild behavior of the neutral component, the charged component manifests itself as a distinct structure near the $D^{*+} D^{-}$ threshold at $3.880$ GeV, in the $M_{\bar{D}^{*0} D^0}$ invariant mass distribution of the spin density matrix element $ρ^{D^*}_{00}$. Hence the line shape of $ρ^{D^*}_{00}$ near this structure depends sensitively on the proportions of the two configurations. We propose high-precision measurements of this matrix element by future BESIII and Belle experiments to elucidate how a molecular $X(3872)$ state is composed.

hep-ph↗

arXiv2025

$Δ(1232)$ production in the $γp \to ϕπp$ reaction

In this work, the production of baryon resonances in the $γp \to ϕπp$ reaction near threshold is investigated within an effective Lagrangian approach. incorporates intermediate resonances, including $Δ(1232)$, $N(1440)$, $N(1520)$, and $N(1535)$, alongside non-resonant background contributions. The results indicate that the reaction is dominated by the $Δ(1232)$ excitation near threshold. A key focus of this study is the exploration of the $a_0(980)$ meson exchange in the $Δ(1232)$ production, as this reaction offers a unique opportunity to probe the poorly known $Δ(1232)N a_0$ coupling. We demonstrate that the parity asymmetry ($P_σ$), accessible through the $ϕ$-meson's spin density matrix elements, serves as a suitable experimental observable to identify the contribution from the $a_0(980)$ exchange.

nucl-th↗

arXiv2025

Study on charmonium(-like) mesons within a diabatic approach

In this work, we study the charmonium(-like) spectrum below 4.1 GeV using the diabatic approach, which offers a unified description of conventional and unconventional heavy meson states. Compared to previous studies, we consider a more realistic $c\bar c$ potential with including the spin-dependent interactions, which allows us to obtain more states and get more insights on the charmonium spectrum. Based on our calculation, we obtain the masses of the charmonium spectrum which align with the experimental data well. We also present the probabilities of finding various components, i.e. $c\bar c$ or meson-meson pair, in those states. Our results support the arguments that the $χ_{c1}(3872)$, $ψ(4040)$ and $χ_{c2}(3930)$ have significant molecular components. In addition, our calculations show that the $χ_{c0}(3860)$ and $ψ(3770)$ can be looked as the candidates for the charmonium states $χ_{c0}(2P)$ and $ψ(1D)$, respectively.

hep-ph↗

arXiv2024

Search for the $Σ(1380)1/2^-$ state in $Λ^+_c \to γπ^+ Λ$ decay by triangle singularity

In this work, we investigate the resonance production in $Λ^+_c \to γπ^+ Λ$ decay through the triangle singularity (TS) mechanism, within an effective Lagrangian approach. We find that the appropriate loop decay process could develop a triangle singularity in the invariant mass $M_{πΛ}$ around $1.35$ GeV, with the shape depending on the quantum numbers of $Σ^*$ states that couple to the final $πΛ$ system. Especially, the $Σ(1380)1/2^-$ state newly predicted in the pentaquark model, if exists, significantly enhances the TS contribution and sharpens the TS peak due to the $S$-wave $Σ^*πΣ$ vertex in the loop. Therefore, the existence of the $Σ(1380)1/2^-$ state can be examined by measuring the TS signal in $Λ^+_c \to γπ^+ Λ$. Considering also possible tree-level diagrams, we additionally obtain the branching ratio ${\rm Br}(Λ^+_c \to γπ^+ Λ)\simeq 1.5\times 10^{-5}$. We suggest the investigation of this reaction by future BESIII, LHCb, and Belle experiments.

hep-ph↗

arXiv2023

Triangle singularity in the $J/ψ\to γ\bar{p} Δ$ decay

In this work, we study the role of triangle singularity in the $J/ψ\to γ\bar{p} Δ$ decay. We find that through a triangle mechanism, involving a triangle loop composed by $ω$, $π$ and $p$, this decay may develop a triangle singularity and produce a visible peak in the invariant mass $M_{γΔ}$ around 1.73 GeV with a width of 0.02 GeV. Such a triangle mechanism may also cause significant spin effects on the final $Δ$, which can be detected by measuring its spin density matrix elements. Our calculations show that the branching ratios due to the triangle mechanism is Br($J/ψ\to γ\bar pΔ,Δ\to πp$)=$1.058\times 10^{-6}$. Hopefully, this reaction can be investigated at BESIII and future experiments, e.g. Super Tau-Charm Facility, and the narrow width of the induced structure, the moving TS position and the distinct features of the spin density matrix elements of the $Δ$ may serve as signals for the triangle singularity mechanism.

hep-ph↗

arXiv2022

Studying triangle singularity through spin observables

In this work, we study the spin density matrix element $ρ_{00}$ of the $ϕ$ in the decay $J/ψ\rightarrow ηπϕ$. In previous studies, a band around 1.4 GeV on the $π^0ϕ$ distribution in Dalitz plot was reported by the BESIII Collaboration. This structure may be caused by the production of a resonance or the triangle singularity mechanism. We find that the predictions of the spin density matrix elements of the final $ϕ$ based on these mechanisms show distinct features. Thus the measurement of the spin density matrix elements of the $ϕ$ in this reaction may offer an alternative way to study the triangle singularity and to clarify the reaction mechanisms, i.e. resonance production or kinematic effects. This work also shows the potential of spin observables in studying kinematic singularities.

hep-ph↗

arXiv2022

Generation of arbitrarily polarized muon pairs via polarized $e^-e^+$ collision

Generation of arbitrarily spin polarized muon pairs is investigated via polarized $e^-e^+$ collision. We calculate the fully spin-resolved cross section ${\rm d}σ_{e^-e^+\rightarrow μ^-μ^+}$ and utilize the Monte Carlo method of binary collision to describe the production and polarization processes of muon pairs. We find that, due to the dependence of mixed helicities on the scattering angle, arbitrarily polarized muon pairs with both of the longitudinal and transverse spin components can be produced. The collision of tightly collimated electron and positron beams with highly longitudinal polarization and nC charge can generate about $40\%$ muon pairs with longitudinal polarization and about $60\%$ muon pairs with transverse polarization. The compact high-flux $e^-e^+\rightarrowμ^-μ^+$ muon source could be implemented through the next-generation laser-plasma linear collider, and would be essential to facilitate the investigation of fundamental physics and the measurement technology in broad areas.

hep-ph↗

arXiv2021

Signatures of linear Breit-Wheeler pair production in polarized $γγ$ collisions

Laser-driven brilliant controllable polarized $γ$-photon sources open the way for designing compact $γγ$ collider, which enable the large yield of linear Breit-Wheeler (LBW) pairs in a single shot and thus provide an opportunity for the investigation of polarized LBW process. In this work we investigate the polarization characteristics of LBW pair production via our developed spin-resolved binary collision simulation method. Polarization of $γ$-photons modifies the kinematics of scattering particles and induces the correlated energy-angle shift of LBW pairs, and the latter's polarization characteristic depends on the helicity configures of scattering particles. Our method confirms that the polarized $γγ$ collider with an asymmetric setup can be performed with currently achievable laser facilities to produce abundant polarized LBW pairs, fulfilling the detection power of polarimetries. The precise knowledge of polarized LBW process is in favor of the calibration and monitor of polarized $γγ$ collider, and could enhance the opacity of $γ$-photons in high-energy astrophysical objects to exacerbate the inconsistency between some observations and standard models.

hep-ph↗

arXiv2020

Polarization of $Λ(1405)$ in the $γp \rightarrow K^+ πΣ$ reaction

In this paper, we study the polarization of the $Λ(1405)$ in the $γp \rightarrow K^+ πΣ$ reaction within an effective Lagrangian approach and isobar model. In our model, the $Λ(1405)$ is excited through the t-channel $K/K^*$ exchanges and u-channel hyperon exchange. Compared to previous studies, we also include the contribution from a contact term, which is necessary for our model to interpret the polarization of the $Λ(1405)$. In addition, we also discuss the possibility to verify the proposed two-pole structure of the $Λ(1405)$ using the polarization data. We find that the polarization of the $Λ(1405)$ or the polarization of the final $Σ$ in this reaction is sensitive to the invariant mass $M_{πΣ}$. Thus the measurement of the dependence of the $Λ(1405)$ polarization on the $M_{πΣ}$ can offer valuable information about the pole structure of the $Λ(1405)$.

nucl-th↗

arXiv2020

Studying $Λ^*$ resonances in the $p \bar p \rightarrow Λ\barΛη$ reaction

In this work, we make a theoretical study on the $p \bar p \rightarrow Λ\barΛη$ reaction for antiproton beam energy from threshold to 4GeV within an effective Lagrangian approach and isobar model. By assuming this reaction is dominated by the excitation of $Λ$ and $\bar Λ$ resonances in intermediate states, we calculate the total cross sections and give the predictions of the angular distribution and invariant mass spectrum of final particles. In particular, we discuss the possibility to verify the existence of a narrow $Λ$ resonance found in the process of $K^- p\to ηΛ$ in the present reaction. It shows that the $p \bar p \rightarrow \bar ΛΛη$ reaction can provide us with valuable information about the $Λ$ resonances having significant couplings to $\bar K N$ and $Λη$ channels. Thus the experimental data of this reaction will be a good supplement to the $\bar K N\toηΛ$ scattering data for studying $Λ$ resonances.

hep-ph↗

arXiv2019

Nucleon resonance production in the $γp \to pηϕ$ reaction

In this work, we perform a study of nucleon resonance production in the $γp \to pηϕ$ reaction within an effective Lagrangian approach. In our model, we consider the excitation of the $N^*(1535)$, $N^*(1650)$, $N^*(1710)$ and $N^*(1720)$ in the intermediate state and the background term. We find that this reaction is dominated by the excitation of the $N^*(1535)$ in the near threshold region. Especially, we study the possible role of the scalar meson exchange in this reaction. It is found that the $f_0(980)$ exchange may give a significant contribution and the parity asymmetry can be used to identify its role in this reaction.

hep-ph↗

arXiv2013

The role of $N^*(2120)$ nucleon resonance in $KΛ(1520)$ photon and hadronic productions

The associate $KΛ(1520)$ photon and hadronic production in the $γp \to K^+Λ(1520)$, $p p \to p K^+ Λ(1520)$ and $π^- p \to K^0 Λ(1520)$ reactions are investigated within the effective Lagrangian approach and the isobar model. We are interested in the contribution from the $N^*(2120)$ (previously called $N^*(2080)$) resonance, which has a significant coupling to the $KΛ(1520)$ channel. The theoretical results show that the current experimental data for the $γp \to K^+Λ(1520)$ reaction favor the existence of the $N^*(2120)$ resonance, and that these measurements can be used to further constrain its properties. We present results, including the $N^*(2120)$ contribution, for total cross sections of the $γp \to K^+Λ(1520)$, $π^- p \to K^0 Λ(1520)$, and $p p \to p K^+ Λ(1520)$ reactions. For this latter one, we also calculate invariant mass and Dalitz plot distributions.

nucl-th↗

arXiv2013

Coupling constant for $Λ(1405)\bar{K}N$

The value of the $Λ(1405){\bar K}N$ coupling constant $g_{Λ(1405)\bar{K}N}$ is obtained by fitting it to the experimental data on the total cross sections of the $K^-p \to π^0Σ^0$ reaction. On the basis of an effective Lagrangian approach and isobar model, we show that the value $|g_{Λ(1405)\bar{K}N}| = 1.51 \pm 0.10$ could be extracted from the available experimental data by assuming that the $s-$channel $Λ(1405)$ resonance plays a dominant role, whereas, the background contributions from the $s-$channel $Λ(1115)$, $t-$channel $K^*$ and $u-$channel nucleon pole processes are small and can be neglected. However, the $u-$channel nucleon pole diagram may also give an important contribution in the present calculations. After the background contributions are taken into account, the above value of $g_{Λ(1405)\bar{K}N}$ is reduced to $|g_{Λ(1405)\bar{K}N}| = 0.77 \pm 0.07$, which is not supported by the previous calculations and the recent CLAS measurements. The theoretical calculations on differential cross sections are also presented, which can be checked by future experiments.

nucl-th↗

arXiv2013

Role of the $N^*(2080)$ in $pp \to pK^+ Λ(1520)$ and $π^- p \to K^0 Λ(1520)$ reactions

We investigate the $Λ(1520)$ hadronic production in the $p p \to p K^+ Λ(1520)$ and $π^- p \to K^0 Λ(1520)$ reactions within the effective Lagrangian method. For $π^- p \to K^0 Λ(1520)$ reaction, in addition to the "background" contributions from $t-$channel $K^*$ exchange, $u-$channel $Σ^+$ exchange, and $s-$channel nucleon pole terms, we also consider the contribution from the nucleon resonance $N^*(2080)$ (spin-parity $J^P = 3/2^-$), which has significant coupling to $KΛ(1520)$ channel. We show that the inclusion of the nucleon resonance $N^*(2080)$ leads to a fairly good description of the low energy experimental total cross section data of $π^- p \to K^0 Λ(1520)$ reaction. From fitting to the experimental data, we get the $N^*(2080)Nπ$ coupling constant $g_{N^*(2080)N π} = 0.14 \pm 0.04$. By using this value and with the assumption that the excitation of $N^*(2080)$ is due to the $π^0$-meson exchanges, we calculate the total and differential cross sections of $p p \to p K^+ Λ(1520)$ reaction. We also demonstrate that the invariant mass distribution and the Dalitz Plot provide direct information of the $Λ(1520)$ production, which can be tested by future experiments.

nucl-th↗

arXiv2013

Nucleon resonance production in $K^+N$ interactions

In this work, we discuss the possibility of studying nucleon resonances in the $K^+N$ interactions. Based on our model calculations, it is found that the hyperon exchange plays an important role for the excitation of nucleon resonances in the $K^+N$ interactions. Therefore, the studies on nucleon resonance production in the $K^+N$ interactions can offer us valuable information about the couplings of nucleon resonances with strange particles. By selecting suitable decay channels of nucleon resonances, some reactions are also suitable to look for missing resonances.

nucl-th↗

arXiv2012

Mechanism of $K^- p \to ηΛ$ reaction near threshold

Within an effective Lagrangian approach, we investigate the reaction mechanism of $K^- p\to ηΛ$ near threshold. It is found that a new $D_{03}$ resonance, with mass $M=1668.5\pm 0.5$MeV and width $Γ=1.5\pm0.5$MeV, is needed to interpret the experimental data reported by the Crystal Ball collaboration. To verify our results, remeasurements on the differential cross sections and $Λ$ polarization in this reaction will be helpful. Furthermore, we also show that the reaction $p\bar p\to Λ\bar Λη$ is a good place to look for this new resonance if it exists.

hep-ph↗