arXiv subjects

Peng-Yu Niu

Publications and source records attributed to Peng-Yu Niu.

13 recordsLinked to original sources

arXiv2026

Thermal width shift of $\Delta^{++}$ in a pion gas

We compute the thermal width shift of the $\Delta^{++}$ resonance induced by a pion gas within a nonrelativistic effective field theory framework. The $\Delta^{++}$ self-energy is evaluated from pion-forward-scattering diagrams with intermediate proton and $\Delta$ states, weighted by the thermal pion distribution. Analytical expressions for the imaginary part of the self-energy yield the temperature-dependent width correction $\delta\Gamma(T)$. The width increases with temperature, reaching approximately $6$~MeV at $T \approx 160$~MeV. When the temperature-dependent $\Delta$ and nucleon masses from an NJL-model chiral restoration scenario are incorporated, the width shift becomes non-monotonic, peaking near $T \approx 140$~MeV---a consequence of the competition between collisional broadening and the shrinking $\Delta \to N\pi$ phase space as the $N$--$\Delta$ mass gap closes. Applying our formalism to STAR data for $\Delta^{++}$ in d+Au collisions at $\sqrt{s_{NN}} = 200$~GeV, we extract a temperature $T \approx 300$~MeV at $p_t = 900$~MeV, consistent with the experimental extraction within errors. This value significantly exceeds the hadronic-phase temperature, explicitly demonstrating that the observed $\Delta^{++}$ width shift is not solely of pion-gas origin---genuine hot-medium and collective-flow contributions must be substantial.

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arXiv2026

The heavy flavor conserving hadronic weak decay of the ground-state bottom baryons

In this work the heavy flavor conserving (HFC) hadronic weak decays of bottom baryons are studied in the framework of the nonrelativistic constituent quark model (NRCQM). We show that the pole terms play an indispensable role in the description of the branching ratio of $\Xi_b^-\to \Lambda_b^0 \pi^-$. With the pole terms included we can make reliable predictions for $\Xi_b^0\to \Lambda_b^0 \pi^0$. A combined study of the HFC hadronic weak decays allows us to make a reasonable prediction for $\Omega_b^-\to\Xi_b^{-(0)}\pi^{0(-)}$, which can be searched for at LHCb and Belle-II experiments.

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arXiv2026

Why is the $Z_c(3900)$ absent in the $h_c\pi$ final state?

In this work, we perform a comprehensive phenomenological analysis of the exotic hadronic states $Z_c(3900)$, $Z_c(4020)$, $Z_b(10610)$ and $Z_b(10650)$ within the framework of Heavy Quark Spin Symmetry (HQSS) and its violation. By constructing S-wave contact interactions between elastic ($D\bar{D}^*/D^*\bar{D}^*$ or $B\bar{B}^*/B^*\bar{B}^*$) and inelastic ($J/\psi\pi, h_c\pi$ or $\Upsilon\pi$, $h_b\pi$) channels, we solve the Lippmann-Schwinger equation to obtain physical production amplitudes and perform a global fit to experimental invariant-mass spectra. Our results demonstrate a striking difference between the charm and bottom sectors: HQSS violation is negligible in the bottom system, leading to comparable peak structures for both $Z_b$ states in all hidden-bottom decay channels. In contrast, significant HQSS breaking is required to describe the $Z_c$ system, where the violation is predominantly concentrated in the elastic interactions. This explains the observed selectivity: $Z_c(3900)$ appears prominently only in $J/\psi\pi$, while $Z_c(4020)$ appears only in $h_c\pi$. Pole analysis confirms the molecular nature of the states, with the $Z_c(4020)$ likely arising from a threshold cusp effect. The model's robustness is verified against variations of the form factor and cutoff, showing stable results.

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arXiv2025

Resonance parameters of the vector charmoniumlike state $G(3900)$

Motivated by the updated analysis of the $G(3900)$ by the BESIII collaboration, we perform a global analysis of the cross sections of the $e^+e^-\to D\bar{D}$, $e^+e^-\to D\bar{D}^*+c.c.$, $e^+e^-\to D^*\bar{D}^*$ processes, especially focusing on the properties of the $G(3900)$. As the energy region of interest is limited by the next opening threshold, i.e. the $D_1\bar{D}$ threshold, we focus on the energy region $[3.7,4.25]~\mathrm{GeV}$, where three charmonia $ψ(1D)$, $ψ(3S)$ and $ψ(2D)$ explicitly contribute to the cross sections. By constructing the $P$-wave contact interaction between the $(D,D^*)$ doublet and its antiparticle in the heavy quark limit, we extract the physical scattering amplitude by solving the Lippmann-Schwinger equation. No matter whether three or two charmonium states are included in our framework, we always find a dynamically generated state corresponding to the $G(3900)$, which suggests it to be a $P$-wave dynamically generated state. We also predict several dynamically generated states in the corresponding $1^{-+}$ channel. These states can be further searched for in the electron-positron annihilation process involving the emission of a single photon.

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arXiv2025

Revisit the diquark of $Λ_c$ in the $Λ_c\to ΛK^+$ and $Λ_c\to Σ^0 K^+$ processes

The spatial distributions of $[ud]$ diquark and heavy-light diquark of the SU(3)-flavor antitriplet charmed baryons are investigated by the two singly Cabibbo-suppressed hadronic weak decays, $Λ_c\to ΛK^+$ and $Λ_c\to Σ^0 K^+$ within the nonrelativistic constituent quark model. The above two spatial distributions are reflected by the two parameters $α_ρ$ and $α_λ$, which are the harmonic oscillator strength parameters of the charmed baryons. These two parameters obtain strong constraints from the decay widths of $Λ_c\to ΛK^+$ and $Λ_c\to Σ^0 K^+$. The larger the harmonic oscillator parameter is, the more compact the spatial distribution will become. The current $α_ρ$ and $α_λ$ indicate that neither the light diquark nor the heavy-light diquark turns out to favor a compact structure. In addition, some selection rules, including the ``$Λ$ selection rule'', can be useful for the search of excited baryons in the heavy-flavor baryon hadronic weak decays.

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arXiv2025

The Cabibbo-favored hadronic weak decays of the $Ξ_c$ in the quark model

The Cabibbo-favored hadronic weak decay of the $Ξ_c^+\to Ξ^0π^+$, $Ξ_c^0\to Ξ^-π^+$, $Ξ_c^0\to Ξ^0π^0$, $Ξ_c^0\to Ξ^0η^{(')}$ and $Ξ_c^0\to Ξ^+K^-$ are studied in the non-relativistic constituent quark model. By analyzing their decay mechanisms at the quark level we show that the pole terms are essential for understanding the transition dynamics in addition to the usually considered direct meson emission process and color suppressed process in the charmed baryon hadronic weak decays. The experimentally measurable asymmetry parameters are also predicted in order to further pin down the decay mechanism.

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arXiv2024

The pole structures of the $X(1840)/X(1835)$ and the $X(1880)$

Whether the $N\bar{N}$ interaction could form a state or not is a long standing question, even before the observation of the $p\bar{p}$ threshold enhancement in 2003. The recent high statistic measurement in the $J/ψ\to γ3(π^+π^-)$ channel would provide a good opportunity to probe the nature of the peak structures around the $p\bar{p}$ threshold in various processes. By constructing the $N\bar{N}$ interaction respecting chiral symmetry, we extract the pole positions by fitting the $p\bar{p}$ and $3(π^+π^-)$ invariant mass distributions of the $J/ψ\to γp \bar p$ and $J/ψ\to γ3(π^+π^-)$ processes. The threshold enhancement in the $p\bar{p}$ invariant mass distribution is from the pole on the third Riemann sheet, which more couples to the isospin triplet channel. The broader structure in the $3(π^+π^-)$ invariant mass comes from the pole on the physical Riemann sheet, which more couples to the isospin singlet channel. Furthermore, the large compositeness indicates that there should exit $p\bar{p}$ resonance based on the current experimental data. In addition, we also see a clear threshold enhancement in the $n\bar{n}$ channel, but not as significant as that in $p\bar{p}$ channel, which is useful and compared with further experimental measurement.

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arXiv2023

Doubly charmed baryon decays $Ξ_{cc}^{++}\toΞ_c^{(\prime)+}π^+$ in the quark model

In this work we study the doubly charmed baryon decays $Ξ_{cc}^{++}\toΞ_c^{(\prime)+}π^+$ within the framework of the non-relativistic quark model (NRQM). Factorizable amplitudes are expressed in terms of transition form factors, while nonfactorizable amplitudes arising form the inner $W$-emission are evaluated using current algebra and the pole model and expressed in terms of baryonic matrix elements and axial-vector form factors. Nonperturbative parameters are then calculated using the NRQM. They can be expressed in terms of the momentum integrals of baryon wave functions, which are in turn expressed in terms of the harmonic oscillator parameters $α_ρ$ and $α_λ$ for $ρ$- and $λ$-mode excitation. The measured ratio $R$ of the branching fraction of $Ξ_{cc}^{++}\to Ξ^{\prime +}_cπ^+$ relative to $Ξ_{cc}^{++}\to Ξ_c^+π^+$ can be accommodated in the NRQM with $α_{ρ1}$ and $α_{ρ_2}$ being in the vicinity of 0.51 and 0.19, respectively, where $α_{ρ1}$ is the $α_ρ$ parameter for $Ξ_{cc}^{++}$ and $α_{ρ2}$ for $Ξ_{c}^{(\prime)+}$. Decay asymmetries are predicted to be $-0.78$ and $-0.89$ for $Ξ_c^+π^+$ and $Ξ_c^{\prime +}π^+$ modes, respectively, which can be tested in the near future. We compare our results with other works and point out that although some other models can accommodate the ratio $R$, they tend to lead to a branching fraction of $Ξ_{cc}^{++}\to Ξ_c^+π^+$ too large compared to that inferred from the LHCb measurement of its rate relative to $Ξ_{cc}^{++}\toΛ_c^+ K^- π^+π^+$.

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arXiv2022

Determine the quantum numbers of $X(6900)$ from photon-photon fusion in ultra-peripheral heavy ion collisions

We study the production of the $X(6900)$ through the $J/ψJ/ψ$ decay channel in the ultra-peripheral heavy ion collisions at the LHC energy region. The potential quantum numbers of $X(6900)$ would be $0^{\pm +}$ and $2^{\pm+}$. We find that the transverse momentum and the polar angle distributions of $X(6900)$ can be used to distinguish these four potential quantum numbers. These typical distributions stem from the linearly polarized photon from the fast-moving nuclei and can be measured with the LHC experiments in further.

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arXiv2021

Study of heavy quark conserving weak decays in the quark model

Within the framework of a constituent quark model, we investigate the heavy quark conserving weak decays of $Ξ_c$ and $Ξ_b$. This process involves elementary transitions of $us\to du$ or $s\to ud \bar u$ with the heavy quark as a spectator, while for the charmed baryon in the initial state it can also occur via $cs\to dc$ to conserve the heavy quark flavor in the weak decays. It shows that the heavy quark symmetry (HQS) plays an essential role in the processes where the heavy quark acts as a spectator. For the $Ξ_c$ decays, the dominance of the pole terms in the parity-conserving transitions is evident. This can naturally explain the sizeable branching ratio for $Ξ_c^0\toΛ_cπ^-$ as recently reported by LHCb. The same mechanism predicts a large branching ratio for $Ξ_c^+\toΛ_cπ^0$. In contrast, the decays of $Ξ_b$ will only go through the parity-violating processes because of the HQS. In addition, the branching ratios of the $Ξ_c^+\to Λ_c π^0$ and $Ξ_b^0\to Λ_b π^0$ processes are also predicted for the further experimental measurement.

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arXiv2020

Hyperon Weak Radiative Decay

We revisit the hyperon weak radiative decays in the framework of the non-relativistic constituent quark model. This study confirms the nonlocal feature of the hyperon weak radiative transition operators which are dominated by the pole terms, and an overall self-consistent description of the available experimental data for the Cabibbo-favored hyperon weak radiative decays is achieved. It provides a natural mechanism for evading the Hara theorem, where sizeable parity-violating contributions can come from the intermediate orbital excitations. Cancellations between pole terms also explain significant SU(3) flavor symmetry breaking manifested by the experimental data. We also discuss several interesting selection rules arising from either the electromagnetic or the weak interaction vertices. These features suggest nontrivial relations among different hyperon decays.

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arXiv2020

Hadronic weak decays of $Λ_c$ in the quark model

The hadronic weak decays of $Λ_c$ are studied in the framework of a constituent quark model. With the combined analysis of the Cabbibo-favored processes, $Λ_c\to Λπ^+$, $Σ^0π^+$ and $Σ^+π^0$, we confirm that the non-factorizable transition mechanisms play a crucial role in the understanding of their compatible branching ratios. We emphasize that the SU(3) flavor symmetry breaking effects, which is generally at the order of $1\sim 2\%$, can be amplified by the destructive interferences among the pole terms in the diagrams with internal conversion. Some contributions are sensitive to the spatial distribution of the scalar-isoscalar light-quark sector in the $Λ_c$, and its overlap with the light quarks in the final state hyperon. Namely, a compact diquark configuration is disfavored.

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arXiv2019

The mass splitting among the isospin multiplets of light vector mesons

By including the strong isospin symmetry breaking effects and the electromagnetic contributions between the pseudoscalar mesons, we calculate the phase shifts of the $P$-wave $ππ$ and $Kπ$ scattering up to $\mathcal{O}(p^4)$ in the framework of the SU(3) chiral perturbation theory (ChPT) and coupled channel inverse amplitude method. We re-fit the low energy constants with the present meson-meson scattering data and derive the mass differences for the charged and neutral iso-multiplets of $ρ$ and $K^{*}$. Our results show that the mass difference between $ρ^\pm$ and $ρ^0$ is very small while the mass difference between the charged and neutral $K^*$ can reach a relatively large value of $m_{K^{*0}}-m_{K^{*+}}= 2.91^{+1.43}_{-1.41}$ MeV. This full one-loop ChPT calculation would shed some light towards a better understanding of the long-standing puzzle about the $K^*$ mass splitting.

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