arXiv subjects

Yupeng Yan

Publications and source records attributed to Yupeng Yan.

At least 19 recordsLinked to original sources

arXiv2026

Separating Equation-of-State Dynamics from Hadronic Rescattering in Low-Mass Dileptons

We investigate low-mass dilepton emission as a probe of the QCD equation of state and phase structure within non-equilibrium chiral fluid dynamics, comparing first-order phase-transition and crossover scenarios at $\sqrt{s_{\rm NN}}=2.20-6.20$~GeV. To disentangle effects of the macroscopic equation-of-state dynamics from conventional hadronic in-medium modifications, the $\rho$ and $\omega$ meson self-energies are calculated from the same resonance-driven forward-scattering amplitudes in both scenarios. We find two temporally distinct signatures of the first-order phase transition: an early enhancement in the vector-meson pole region associated with the non-equilibrium evolution through the phase transition, and a later enhancement of the low-mass continuum driven by reheating and the prolonged fireball evolution. Both effects survive integration over the complete space-time evolution, with the pole-mass region retaining the strongest sensitivity to the phase structure. Across the investigated beam energies, the pole-mass excitation function retains a pronounced sensitivity to first-order transition dynamics at low collision energies, identifying this mass region as a promising target for future dilepton beam-energy scans.

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arXiv2026

Charmed nuclei and exotic charmed meson production at CBM@FAIR and ALICE@LHC

We make predictions for the expected multiplicities of exotic charmed hadrons and charmed nuclei in Au+Au collisions at SIS100 and LHC beam energies, using input on light hadron and charm production from the UrQMD transport model, and applying the Thermal-FIST model. We demonstrate that the CBM experiment has the capability to explore these states with production rates of one per 3 seconds for $\chi_{c0}(1P)$ and $\chi_{c1}(1P)$, and one every 3 minutes for $X(3872)$ at the expected data taking rates. Due to the higher baryon density at CBM compared to the LHC, charmed nuclei, if they exist, will be equally abundant at CBM as at the LHC, even though the total charm production at CBM is much lower.

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arXiv2025

Systematic study of exotic $1^{-+}$ tetraquark spectroscopy

The masses of exotic quantum-number $1^{-+}$ compact tetraquark states are calculated in a constituent quark model, where a Cornell-like potential is employed as the central potential, spin-spin and spin-orbit coupling derived from the Breit-Fermi interaction are treated as hyperfine corrections, and model parameters are taken from previous works. The ground state $1^{-+}$ P-wave tetraquarks are predicted at 1.9, 4.2, and 6.6~GeV for the light, charmonium-like, and fully-charm sectors, respectively. The decay width ratios of $1^{-+}$ tetraquark states are calculated for two-body strong decay channels within the rearrangement mechanism, including $\omega h_1$ and $\eta f_1$ for isospin $I=0$ light tetraquarks, $\rho h_1$ and $\pi f_1$ for isospin $I=1$ light tetraquarks, $\pi/\eta+\chi_{c1}$ and $\rho/\omega + h_c$ for charmonium-like tetraquarks, and $\eta_c \chi_{c1}$ and $J/\psi h_c$ for fully-charm tetraquarks. The theoretical results are compared with the observed exotic $1^{-+}$ states, and promising search channels for $1^{-+}$ tetraquarks are discussed. The work suggests that $\eta_1(1855)$ is unlikely to be a compact tetraquark state.

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arXiv2025

Three-body final state interactions in $B^+\to D\bar{D}K^+$ decays

This paper presents a detailed analysis of the three-body final state interactions in the $B^+\to D\bar{D}K^+$ process, whose phase space is sufficient small. To precisely extract the resonance parameters, for instance the $\chi_{c0/2}(3930)$ in the $D\bar{D}$ invariant mass distributions, in this process, one has to take into account final state interaction, especially the three-body final state interaction. We employ the dispersive Khuri-Treiman formalism, combined with a parameterization of the $D\bar{D}$ interaction based on Heavy Quark Spin Symmetry. By performing a simultaneous fit to the experimental data from LHCb, BaBar, and Belle collaborations, the scheme with three-body interaction successfully describes the invariant mass distributions of the three two-body subsystems. We precisely extract the pole structures of $\chi_{c0}(3930)$ and $\psi(3770)$ as $3.913-0.018i~\mathrm{GeV}$ and $3.764-0.002i~\mathrm{GeV}$ in $B^+$ decay. By performing the pole trajectory analysis on a uniformized complex plane, we find that both of them stem from the input bare state.

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arXiv2025

Helicity amplitudes of $N(1520)$ and $N(1535)$ including pentaquark components

We investigate the helicity amplitudes of the $N(1520)$ and $N(1535)$ resonances in the electromagnetic transition process $\gamma^*p\to N^*$, where the $N(1520)$ and $N(1535)$ are assumed to include both the $L=1$ three-quark and $L=0$ spatial symmetric $q^4\bar q$ pentaquark components. The helicity transition amplitudes $A_{1/2}$, $A_{3/2}$ (for spin 3/2 states) and $S_{1/2}$ are computed within the constituent quark model. The inclusion of the $q^4 \bar q$ pentaquark components via the $\gamma^*\to q\bar q$ diagram significantly improves the theoretical description of the helicity amplitudes for both $N(1520)$ and $N(1535)$, yielding a closer agreement with experimental data compared to the pure three-quark picture. The work reveals that the $N(1520)$ and $N(1535)$ resonances may contain a considerable pentaquark components.

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arXiv2025

Radiative decay of $\chi_{c1}$ states in effective Lagrangian approach

The $\chi_{c1}(3872)$ state, first observed by the Belle collaboration with its quantum numbers identified as $J^{PC} = 1^{++}$, has been the subject of extensive research due to its intriguing properties. Several theoretical interpretations have been proposed to explain its unique characteristics, including the $\chi_{c1}(2P)$ assignment, a molecular $\bar{D}^{*}D/\bar{D}D^{*}$ configuration, a coupled-channel framework incorporating $c\bar{c}$ and di-meson degrees of freedom, and the compact tetraquark hypothesis. However, challenges remain in reconciling its mass coincidence with the threshold and the observed isospin violation within both the pure $c\bar{c}$ and compact tetraquark models. In this study, we examine the radiative decays of the $\chi_{c1}(1P)$ and $\chi_{c1}(3872)$ states in an effective field theory framework, incorporating triangle loops of $D$ and $D^{*}$ mesons. The model parameters are calibrated based on the observed branching fraction of the radiative decay mode $\chi_{c1}(1P) \to J/\psi \gamma$. Utilizing these fixed parameters, we predict the branching fractions $R_{\chi_{c1}(3872) \to J/\psi \gamma} \sim 10^{-1}$ and $R_{\chi_{c1}(3872) \to \psi(2S) \gamma} \sim 10^{-2}$, and the relative fraction $\mathcal{R}_{\Psi\gamma} \approx 0.109$. The work supports the argument that the $\chi_{c1}(3872)$ is unlikely a $c\bar{c}$ state.

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arXiv2025

Study of $1^{--}$ P wave charmoniumlike and bottomoniumlike tetraquark spectroscopy

The masses of $1^{--}$ P-wave charmonium-like and bottomonium-like tetraquark states are calculated in a constituent quark model (CQM) where the Cornell-like potential and Breit-Fermi interaction are employed. All model parameters were imported from previous work, and predetermined by studying the low-lying conventional S- and P-wave light, charmed, bottom, charmonium, and bottomonium meson mass spectra. The lowest $1^{--}$ tetraquark mass is predicted to be around 4.15 GeV. The decay widths of $1^{--}$ P-wave tetraquark states are calculated for possible two-body strong decay channels within the rearrangement mechanism, including $\omega \chi_{cJ}$ and $\eta J/\psi$ for charmonium-like tetraquarks, and $\omega \chi_{bJ}$ for bottomonium-like tetraquarks. The theoretical results are compared with the selected exotic states, also known as Y states, and tentative assignments are suggested. This study suggests that $\psi(4230)$, $\psi(4360)$, $\psi(4660)$, and $\Upsilon$(10753) may be P-wave tetraquark states and that multiple states might exist around 4.36 GeV.

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arXiv2024

Determining the Meson Cloud Contribution of Nucleon Electromagnetic Form Factor Using Dispersion Relation

We explore the meson cloud contribution to nucleon electromagnetic form factors in dispersion relation approach. In our calculations, experimental data on transition amplitudes for pion-nucleon scatterings are taken directly as inputs, with the assumption that the photon-pion interaction dominates over other meson-photon couplings. Combining with the quark core contribution evaluated in quark model, the proton electromagnetic form factors are well reproduced in the work. The resulting mean-square charge radius of the proton agrees well with experimental data, and the quark core radius is reasonable.

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arXiv2024

Electromagnetic form factors of the transition from the Delta to the nucleon

The low-energy electromagnetic form factors of the $\Delta$(1232)-to-nucleon transition are derived combining dispersion theory techniques and chiral perturbation theory. The form factors are expressed in terms of the well-understood pion vector form factor and pion-baryon scattering amplitudes. Nucleon and Delta exchange terms and contact terms constitute the input for these pion-baryon amplitudes. The framework is formulated for all form factors. When comparing to experimental data in the spacelike region of $e^- N \to e^- \Delta$ scattering, the focus lies on the numerically dominant magnetic dipole transition form factor. Fitting two subtraction constants (one for the scattering amplitude, one for the form factor) yields a very good description of this dominant form factor up to photon virtualities of about 0.6 GeV. After determining the subtraction constants in the spacelike region and at the photon point, respectively, predictions for the timelike region of Dalitz decays $\Delta \to N \, e^+ e^-$ are presented.

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arXiv2023

$P_c$ states in the mixture of molecular and pentaquark pictures

We systematically study hidden charm pentaquark states in the constituent quark model with a general Hamiltonian for multiquark systems, considering the coupling between the $Σ_c^{(*)}\bar{D}^{(*)}$ molecular states and the $q^3c\bar c$ compact pentaquark states by the one-gluon exchange hyperfine interaction. The ground state hidden-charm pentaquark mass spectra and the strong decay widths are calculated. This work suggests that $P_c(4312)$, $P_c(4457)$ and $P_c(4380)$ resonances might be mainly $Σ_c \bar D$, $Σ_c \bar D^*$ and $Σ_c^* \bar D$ hadronic molecules respectively, and $P_c(4440)$ might include sizable pentaquark components.

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arXiv2023

Determination of parameters of a potential model for tetraquark study by studying all S-wave mesons

The masses of low-lying S-wave mesons are evaluated in a constituent quark model (CQM) where the Cornell-like potential and one-gluon exchange spin-spin interaction are employed. To make the model applicable to both the light and heavy quark sectors, we introduce mass-dependent coupling coefficients. There are four free parameters in the model, which are determined by comparing the theoretical results with experimental data. The established model with one set of parameters may be applied to study higher excited meson states as well as multiquark systems in both the light and heavy quark sectors.

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arXiv2023

Study of light tetraquark spectroscopy

We calculate the masses of the $qq\bar q\bar q$ tetraquark ground state and first radial excited state in a constituent quark model where the Cornell-like potential and one-gluon exchange spin-spin coupling are employed. The three coupling parameters for the Cornell-like potential and one-gluon exchange spin-spin coupling are proposed mass-dependent in accordance with Lattice QCD data, and all model parameters are predetermined by studying light, charmed and bottom mesons. The theoretical predictions for light tetraquarks are compared with the observed exotic meson states in the light-unflavored meson sector, and tentative assignments are suggested. The work suggests that the $f_0(1500)$ and $f_0(1710)$ might be ground light tetraquark states with $J=0$.

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arXiv2023

Mass spectrum of $1^{--}$ heavy quarkonium

We calculate the masses and leptonic decay widths of the bottomonium $b\bar b$ and charmonium $c\bar c$ states in a constituent quark model where the Cornell-like potential and spin-dependent interaction are employed, with all model parameters predetermined by studying ground and first radial excited states of S- and P-wave heavy quarkonium mesons. By comparing the theoretical predictions for $J^{PC}=1^{--}$ quarkonium states with experimental data and considering possible mixtures of $nS$ and $(n-1)D$ states, we provide tentative assignments for all observed $J^{PC}=1^{--}$ heavy quarkonia. The work suggests that the $\Upsilon$(10860) and $\Upsilon$(11020) are $b\bar b$ $5S-4D$ mixture states, and the $\psi$(4360) and $\psi$(4415) are largely $4S$ and $3D$ $c\bar c$ states respectively. The $\psi$(4260) may not be accommodated with the conventional meson picture in the present work.

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arXiv2023

Group Theory Analysis of $P_c$ Resonances in Molecular Picture

Hidden-charm pentaquarks are analysed in Group Theory in the baryon-meson molecule picture within the framework of the constituent quark model. The investigation of strong decays of pentaquark resonances reveals that pentaquark states of all quark configurations can decay through the $N J/ψ$ channel while only five pentaquark states may decay in open-charm modes. The partial decay widths in the $pη_c$ channel are in the same order as in the $p J/ψ$ channel for $J^P=1/2^-$ baryon-meson pentaquark states, but the $pη_c$ channel is forbidden for $J^P=3/2^-$ states. The $p η_c$, $Σ_c\bar{D}$ and $Λ_c^+\bar{D}$ channels open for $J^P=1/2^-$ $P_c(4440)$ and $P_c(4457)$ while the $Σ_c^*\bar{D}$ channel opens for $J^P=3/2^-$ $P_c(4440)$ and $P_c(4457)$. For $P_c(4312)$, due to the mass threshold of $Σ_c\bar{D}$ and $Σ_c^*\bar{D}$ higher than 4312 MeV, the $p η_c$ and $Λ_c^+\bar{D}$ channels are open for $J^P=1/2^-$ but no open-charm channel open for $J^P=3/2^-$. We strongly suggest that the spin of the $P_c$ resonances may be determined in experiments by investigating the $p η_c$ and open-charm channels.

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arXiv2022

Study on $Λnn$ Bound State and Resonance

We perform the ab initio no-core shell model (NCSM) calculation to investigate the bound state problem of the three-body $Λnn$ system in chiral next-to-next-to-leading-order NN and chiral leading-order YN interactions. The calculations show that no $Λnn$ bound state exists, but predict a low-lying $Λnn$ resonant state near the threshold with the energy of $E_r= 0.124$ MeV and the width of about $Γ=1.161$ MeV. In searching for $Λnn$ resonances, we extend the NCSM calculation to the continuum state by employing the J-matrix formalism in the scattering theory with the hyperspherical oscillator basis.

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arXiv2022

A possible interpretation of $Λ$ baryon spectrum with pentaquark components

The $Λ$ baryon spectrum is studied within the SU(3) flavor symmetry in a constituent quark model. We found that it is rather difficult to accommodate some negative-parity $Λ$ resonances as single $q^2s$ ($q = u,\,d$ quarks) states in the conventional three-quark picture. The ground $q^3s\bar q$ pentaquark mass spectrum is evaluated and a possible interpretation is proposed in the work: the observed $Λ(1405)1/2^{-}$, $Λ(1670)1/2^{-}$ and $Λ(1800)1/2^{-}$ are three-state mixtures of two $p$-wave $q^2s$ states and one ground $q^3s\bar q$ pentaquark state, so are the $Λ(1520)3/2^{-}$, $Λ(1690)3/2^{-}$ and $Λ(2050)3/2^{-}$ resonances.

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arXiv2022

Estimation of coupling constants for D-meson, charmed, and light baryons in effective Lagrangian approach and quark model

We estimate coupling constants for effective Lagrangians of $D$-meson, charmed, and light baryons from charmed baryon decay processes. First, we calculate decay widths for the processes $Λ_{c} \to DN$, $Σ_{c} \to D Δ$, $Σ_{c} \to D^{*} Δ$, and $Λ_{c} \to D^{*}N$ in effective Lagrangian method and quark model picture with $^{3}P_{0}$ model. By employing the coupling constants for $D^{*} Λ_{c} N$ interaction from several literatures, the strength parameter $λ$ for $^{3}P_{0}$ quark model is fixed in the decay process $Λ_{c} \to D^{*}N$. Then, the coupling constants for the effective Lagrangians of $DΛ_{c}N$, $DΣ_{c}Δ$, and $D^{*}Σ_{c}Δ$ interactions are estimated in the decay channels $Λ_{c} \to DN$, $Σ_{c} \to D Δ$, and $Σ_{c} \to D^{*} Δ$, respectively. These coupling constants will be useful for further studies of charm hadrons.

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arXiv2022

Correcting the $B_A$ coalescence factor at GSI-HADES and RHIC-BES energies

We investigate the coalescence factors $B_2$ and $B_3$ at low collision energies ($\sqrt{s_\mathrm{NN}}<6$ GeV) with special focus on the HADES and RHIC-BES experiments. It is shown that, in order to properly interpret the coalescence factors $B_A$, two important corrections are necessary: I) $B_2$ has to be calculated using the proton $\times$ neutron yields in the denominator, instead of the square of the proton yield, and II) the primordial proton (neutron) densities have to be used for the normalization and not the final state (free) protons (neutrons). Both effects lead to a drastic reduction of $B_2$ and $B_3$ at low energies. This reduction decreases the discrepancy between the volumes extracted from HBT measurements and the volumes extracted from the coalescence factor ($V\propto 1/B_2$). While at HADES and low RHIC-BES energies these corrections are substantial, they become irrelevant above $\sqrt{s_\mathrm{NN}}>6$ GeV. The proposed correction method is model independent and is only based on the measurement of protons, clusters and charged pions.

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