arXiv subjects

Biaogang Wu

Publications and source records attributed to Biaogang Wu.

12 recordsLinked to original sources

arXiv2026

Comprehensive study of $Υ$($n$S) production in Oxygen+Oxygen collisions at LHC

We study bottomonium $Υ$($n$S) production in ${\rm O}+{\rm O}$ collisions at $\sqrt{s_{NN}}=5.36$~TeV, including both cold nuclear-matter (CNM) effects and final-state interactions in a short-lived quark-gluon plasma. The CNM baseline is calculated using the EPPS21 nuclear parton distribution functions together with coherent energy loss and transverse momentum broadening. Hot-medium effects are evaluated with two transport approaches coupled to the same centrality-resolved 3+1D aHydroQP background: the QTRAJ-NLO open-quantum-system calculation, implemented with the {\sc QTraj} code, and the TAMU-NP semiclassical rates, including primordial suppression and regeneration. The CNM effects give a moderate, state-independent suppression, dominated by the nPDF modification. The energy loss and transverse momentum broadening contribution remains at the few-percent level. Both transport approaches predict a sequential suppression pattern, $R_{AA}^{Υ(1\rm{S})}>R_{AA}^{Υ(2\rm{S})}>R_{AA}^{Υ(3\rm{S})}$, with the strongest suppression around midrapidity in central collisions. The suppression of the ground state is similar in the two approaches but differs for the excited states. Since the CNM factor is common to all states, double ratios provide a direct measure of the relative hot-medium suppression. Our results support the conclusion that ${\rm O}+{\rm O}$ collisions at the LHC can produce a short-lived QGP capable of modifying bottomonium yields.

nucl-th↗

arXiv2026

Bottomonium transport in the sQGP at RHIC and the LHC

Bottomonium transport is studied in heavy-ion collisions at RHIC and the LHC by implementing a kinetic rate equation into (3+1)D viscous hydrodynamic simulations of an expanding quark-gluon plasma (QGP). The two main transport parameters are the inelastic reaction rates and equilibrium limits for each individual bottomonium state, $Y$. The former are taken from the thermodynamic $T$-matrix formalism with recent constraints from lattice-QCD and including interference effects and in-medium binding energies, resulting in large rates characteristic of a strongly coupled QGP. The equilibrium limits are evaluated from pertinent in-medium bottomonium and bottom-quark masses. The calculation of observables includes a total of nine $Y$ states (up to 3$S$ and 2$P$) with a feed-down matrix estimated from vacuum branching fractions. At the LHC, the large reaction rates rapidly suppress the initial population of excited states, rendering regeneration their main source even in rather peripheral collisions, while for the more strongly bound ground state $Υ(1S)$, a significant primordial component survives in central collisions. On the other hand, at RHIC energies, regeneration is overall a smaller effect. Together with effects from nuclear absorption, this offers an explanation for the experimental observation that $Υ(1S)$ production at RHIC and the LHC is of comparable magnitude despite the significantly higher temperatures reached in the QGP at the LHC.

nucl-th↗

arXiv2026

Coupled charm and charmonium transport in a strongly coupled quark-gluon plasma

The quark-gluon plasma (QGP) is a strongly coupled medium in which both open and hidden charm particles experience substantial nonperturbative interactions. This poses a major challenge for a quantitative description of charmonium transport in ultra-relativistic heavy-ion collisions, as it requires a mutually consistent treatment of pertinent transport coefficients. In this work, we present a coupled charm-charmonium transport framework for a strongly coupled QGP based on thermodynamic $T$-matrix interactions with recent constraints from Wilson-line correlators (WLCs) computed in lattice QCD. For the first time, the same underlying heavy-light interactions and in-medium spectral functions are used to self-consistently evaluate charm-quark diffusion and charmonium kinetics. In particular, the charmonium equilibrium limit, a critical transport parameter for regeneration, is evaluated in the presence of broad spectral functions. Charm-quark diffusion is simulated via Langevin dynamics and coupled to a Boltzmann equation for charmonium dissociation and regeneration. The equilibrium limit of the statistical model is recovered once charm quarks thermalize, and its extension to describe off-equilibrium is constructed. Preliminary applications to charmonium observables in Pb--Pb collisions at the LHC capture the measured centrality and momentum dependence fairly well.

nucl-th↗

arXiv2026

Bottomonium transport in a strongly coupled quark-gluon plasma

Quarkonium production in high-energy heavy-ion collisions remains a key probe of the quark-gluon plasma formed in these reactions, but the development of a fully integrated nonperturbative approach remains a challenge. Toward this end, we set up a semiclassical transport approach that combines nonperturbative reaction rates rooted in lattice-constrained $T$-matrix interactions with a viscous hydrodynamic medium evolution. Bottomonium suppression is computed along trajectories in the hydrodynamic evolution while regeneration is evaluated via a rate equation extended to a medium with spatial gradients. The much larger reaction rates compared to previous calculations markedly enhance both dissociation and regeneration processes. This, in particular, requires a reliable assessment of bottomonium equilibrium limits and of the non-thermal distributions of the bottom quarks transported through the expanding medium. Within current uncertainties our approach can describe the centrality dependence of bottomonium yields measured in Pb-Pb ($\sqrt{s_{_{\rm NN}}}$=5.02\,TeV) collisions at the LHC, while discrepancies are found at large transverse momenta.

nucl-th↗

arXiv2026

Semiclassical treatment of bottomonium suppression and regeneration in $p+{\rm Pb}$ collisions

We study bottomonium suppression in $p+ {\rm Pb}$ relative to $p+p$ collisions at center-of-mass energies of $\sqrt{s_{NN}}= 5.02$ and 8.16~TeV. Specifically, we combine cold nuclear matter effects (nuclear modifications of the parton densities, energy loss and momentum broadening) with those from hot nuclear matter (suppression and regeneration) by implementing the formation of a quark-gluon plasma in hydrodynamic simulations. Bottomonium transport in the quark-gluon plasma is evaluated semiclassically, employing two different reaction rates. The first includes quasi-free inelastic scattering and gluo-dissociation employing a perturbative coupling to the medium. The second is based on in-medium $T$-matrix calculations where the input potential is constrained by lattice quantum chromodynamics to extract the bottomonium masses and dissociation rates. These semiclassical results are compared to previous calculations in an open quantum systems approach and to the experimental data. Predictions for $χ_b$ suppression at $\sqrt{s_{NN}} = 8.16$~TeV are also presented.

nucl-th↗

arXiv2026

Non-perturbative quarkonium dissociation rates in strongly coupled quark-gluon plasma

Heavy quarks and quarkonia are versatile probes of the transport properties of the hot QCD medium produced in ultra-relativistic heavy-ion collisions (URHICs). A robust description of heavy-flavor transport coefficients requires a microscopic approach that treats the open and hidden heavy-flavor sectors on the same footing. Here, we employ the quantum many-body $T$-matrix formalism to evaluate the dissociation rates of heavy quarkonia in the quark-gluon plasma (QGP). The basic ingredient is the heavy-light $T$-matrix, which utilizes a nonperturbative driving kernel constrained by lattice-QCD data. Its resummation in a ladder series provides a much enhanced interaction strength compared to previously used perturbative coupling to the quasiparticle partons in the QGP. The in-medium quarkonium properties, particularly their temperature-dependent binding energies, are evaluated self-consistently using the same interaction kernel, including interference effects (also referred to as the imaginary part of the heavy-quark potential) as well as off-shell parton spectral functions. We systematically investigate the interplay of these effects and elaborate on the connections to the dipole approximation used in effective field theory.

nucl-th↗

arXiv2026

Recombination of $B_c$ mesons in ultra-relativistic heavy-ion collisions

High-energy heavy-ion collisions have been suggested as a favorable environment for the production of $B_c$ mesons, due to a much larger abundance of charm and bottom quarks compared to elementary reactions. Motivated by recent CMS data for $B_c^+$ production in Pb-Pb($5.02\,$TeV) collisions at the LHC, we deploy a previously developed transport approach for charmonia and bottomonia to evaluate the kinetics of $B_c$ mesons throughout the fireball formed in these reactions. The main inputs to our approach are two transport parameters: the $B_c$'s reaction rate and equilibrium limit. Both quantities are determined by previous calculations via a combination of charm and bottom sectors. In-medium binding energies of $B_c$ mesons are calculated from a thermodynamic $T$-matrix with a lattice-QCD constrained potential, and figure in their inelastic reaction rates. Temperature-dependent equilibrium limits include charm- and bottom-quark fugacities based on their initial production. We compute the centrality dependence of inclusive $B_c$ production and transverse-momentum ($p_T$) spectra using two different recombination models, instantaneous coalescence and resonance recombination. The main uncertainty in the resulting nuclear modification factors, $R_{\rm AA}$, is currently associated with the $B_c$ cross section in elementary $pp$ collisions, caused by the uncertainty in the branching ratio for the $B_c^-\to J/ψμ^-\bar ν$ decay. Our results indicate a large enhancement of the $R_{\rm AA}$ at low $p_T$, with significant regeneration contributions up to $p_T\simeq\,20\,$GeV. Comparisons to CMS data are carried out but firm conclusions will require a more accurate value of the branching ratio, or alternative channels to measure the $B_c$ production in $pp$ collisions.

nucl-th↗

arXiv2026

Charmonium Transport in Ultra-Relativistic Heavy-Ion Collisions at the LHC

We provide an update on our semi-classical transport approach for quarkonium production in high-energy heavy-ion collisions, focusing on $J/ψ$ and $ψ(2S)$ mesons in 5.02 TeV Pb-Pb collisions at the Large Hadron Collider (LHC) at both forward and mid-rapidity. In particular, we employ the most recent charm-production cross sections reported in pp collisions, which are pivotal for the magnitude of the regeneration contribution, and their modifications due to cold-nuclear-matter (CNM) effects. Multi-differential observables are calculated in terms of nuclear modification factors as a function of centrality, transverse momentum, and rapidity, including the contributions from bottom-decay feeddown. For our predictions for $ψ(2S)$ production, the mechanism of sequential regeneration relative to the more strongly bound $J/ψ$ meson plays an important role in interpreting recent ALICE data.

nucl-th↗

arXiv2025

Quarkonium Spectroscopy in the Quark-Gluon Plasma

The properties of bound states are fundamental to hadronic spectroscopy and play a central role in the transition from hadronic matter to a quark-gluon plasma (QGP). In a strongly coupled QGP (sQGP), the interplay of temperature, binding energy and large collisional widths of the partons poses formidable challenges in evaluating the in-medium properties of hadronic states and their eventual melting. In particular, the existence of heavy quarkonia in the QGP is a long-standing problem that is hard to solve by considering their spectral properties on the real-energy axis. We address this problem by analyzing in-medium thermodynamic quarkonium $T$-matrices in the complex energy plane. We first validate this method in vacuum, where the $T$-matrix poles of observed states are readily identified. When deploying this approach to recent self-consistently calculated $T$-matrices in the QGP, we find that poles in the complex energy plane can persist to surprisingly large temperatures, depending on the strength of the in-medium interactions. While the masses and widths of the pole positions are precisely defined, the notion of a binding energy is not due to the absence of thresholds caused by the (large) widths of the underlying anti-/quark spectral functions. Our method thus provides a new and definitive quantum-mechanical criterion to determine the melting temperature of hadronic states in the sQGP while increasing the accuracy in the theoretical determination of transport parameters.

nucl-th↗

arXiv2022

Charmonium, $B_c$ and X(3872) Transport at the LHC

We deploy a kinetic-rate equation to evaluate the transport of $J/ψ$, $ψ(2S)$, $B_c$ and X(3872) in ultra-relativistic heavy-ion collisions and compare their production yields to experimental data from the Large Hadron Collider. The rate equation has two main transport parameters, i.e., the equilibrium limit and reaction rate for each state. The temperature-dependent equilibrium limits include charm- and bottom-quark fugacities based on their initial production. The reaction rates for charmonia, bottomonia and $B_c$ rely on charm- and bottom-quark masses as well as binding energies from a thermodynamic $T$-matrix approach. For the X(3872) particle, its internal structure information is encoded in reaction rates and initial conditions in the hadronic phase via two different scenarios: a loosely bound hadronic molecule vs. a compact diquark-antidiquark tetraquark.

hep-ph↗

arXiv2022

Collectivity of $J/ψ$ Mesons in Heavy-Ion Collisions

The production of $J/ψ$ mesons in heavy-ion collisions at the Large Hadron Collider is believed to be dominated by the recombination of charm and anti-charm quarks in a hot QCD medium. However, measurements of the elliptic flow ($v_2$) of $J/ψ$ mesons in these reactions are not well described by existing calculations of $J/ψ$ recombination for transverse momenta $p_T\geq$4 GeV. Here, we revisit these calculations in two main aspects. By employing the resonance recombination model, we implement distribution functions of charm quarks transported through the quark-gluon plasma using state-of-the-art Langevin simulations, and we account for the space-momentum correlations of the diffusing charm and anti-charm quarks in the hydrodynamically expanding fireball. These improvements extend the relevance of the recombination processes to substantially larger momenta than before. In addition, we revisit the suppression of the primordially produced $J/ψ$ mesons by propagating them through the same hydrodynamic medium, leading to a marked increase of the $v_2$ of this component over previous estimates. Combining these developments into a calculation of the $p_T$-dependent nuclear modification factor and $v_2$ of inclusive $J/ψ$ production in semi-central Pb-Pb collisions at the LHC, we find a good description of the experimental results by the ALICE collaboration. Our results thus resolve the above-mentioned $v_2$ puzzle and imply the relevance of recombination processes for $p_T$'s of up to $\sim$8 GeV.

nucl-th↗

arXiv2021

X(3872) Transport in Heavy-Ion Collisions

The production of the $X(3872)$ particle in heavy-ion collisions has been contemplated as an alternative probe of its internal structure. To investigate this conjecture, we perform transport calculations of the $X(3872)$ through the fireball formed in nuclear collisions at the LHC. Within a kinetic-rate equation approach as previously used for charmonia, the formation and dissociation of the $X(3872)$ is controlled by two transport parameters, i.e., its inelastic reaction rate and thermal-equilibrium limit in the evolving hot QCD medium. While the equilibrium limit is controlled by the charm production cross section in primordial nucleon-nucleon collisions (together with the spectra of charm states in the medium), the structure information is encoded in the reaction rate. We study how different scenarios for the rate affect the centrality dependence and transverse-momentum ($p_T$) spectra of the $X(3872)$. Larger reaction rates associated with the loosely bound molecule structure imply that it is formed later in the fireball evolution than the tetraquark and thus its final yields are generally smaller by around a factor of two, which is qualitatively different from most coalescence model calculations to date. The $p_T$ spectra provide further information as the later decoupling time within the molecular scenario leads to harder spectra caused by the blue-shift from the expanding fireball.

nucl-th↗