arXiv subjects

Baoyi Chen

Publications and source records attributed to Baoyi Chen.

At least 37 records · Page 2Linked to original sources

arXiv2024

Production of doubly charmed hadron $Ξ_{cc}^{++}$ and $T_{cc}^+$ in relativistic heavy ion collisions

Heavy ion collisions provide a unique opportunity for studying the properties of exotic hadrons with two charm quarks. The production of $T_{cc}^+$ is significantly enhanced in nuclear collisions compared to proton-proton collisions due to the creation of multiple charm pairs. In this study, we employ the Langevin equation in combination with the Instantaneous Coalescence Model (LICM) to investigate the production of $T_{cc}^+$ and $Ξ_{cc}^{++}$ which consists of two charm quarks. We consider $T_{cc}^+$ as molecular states composed of $D$ and $D^*$ mesons. The Langevin equation is used to calculate the energy loss of charm quarks and $D$ mesons in the hot medium. The hadronization process, where charm quarks transform into each $D$ state as constituents of $T_{cc}^+$ production, is described using the coalescence model. The coalescence probability between $D$ and $D^*$ is determined by the Wigner function, which encodes the information of the $T_{cc}^+$ wave function. Our results show that the $T_{cc}^+$ production varies by approximately one order of magnitude when different widths in the Wigner function, representing distinct binding energies of $T_{cc}^+$, are considered. This variation offers valuable insights into the nature of $T_{cc}^+$ through the analysis of its wave function. The $Ξ_{cc}^{++}$ is treated as a hadronic state produced at the hadronization of the deconfined matter. Its production is also calculated as a comparison with the molecular state $T_{cc}^+$.

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arXiv2024

Finite size effect on gluon dissociation of J/psi in relativistic heavy ion collisions

Thermal quantities, including the the entropy density and gluon spectrum, of quark matter within a box that is finite in the longitudinal direction are calculated using a bag model. Under the assumption of entropy conservation, the corresponding gluon dissociation rate of J/psi is studied. It reaches a maximum at a certain longitudinal size L_m, below which the suppression is weak even if the temperature becomes higher than that without the finite size effect, and above which the dissociation rate approaches to the thermodynamic limit gradually with increasing longitudinal size of the fireball.

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arXiv2024

Bottomonium evolution with in-medium heavy quark potential from lattice QCD

The static properties and dynamic evolution of bottomonium states in a hot QCD medium are investigated through the Schrödinger equation with complex heavy quark potentials, which are presented recently in lattice QCD study and with three different extractions. This approach builds a direct connection between the in-medium heavy quark potentials from the lattice QCD to the experimental observables. The yields and nuclear modification factors $R_{AA}$ of bottomonium in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02~\rm TeV$ are calculated in this work. Our results show a large suppression of the bottomonium yield in heavy ion collisions due to the large imaginary potential. To understand bottomonium $R_{AA}$ based on lattice QCD potentials, we propose a fomration time for bottomonium states and find that experimental data can be well explained with the heavy quark potential extracted by the Padé fit, which shows no color screening in the real part potential.

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arXiv2023

$J/ψ$ polarization in relativistic heavy ion collisions

Understanding the polarization property of $J/ψ$ is critical to constrain its production mechanism. In addition, the polarization of $J/ψ$ can reveal the impact of strong electromagnetic and vorticity fields in relativistic heavy ion collisions. In this study, we analyzed the yield and polarization of $J/ψ$ in relativistic heavy ion collisions at different centrality and transverse momentum regions, using three different reference frames: the Collins-Soper frame, the helicity frame, and the event plane frame. The polarization of initially produced $J/ψ$ is determined by the NRQCD calculation and is similar to that of $pp$ collisions. However, both unpolarization and transverse polarization are considered for the regenerated $J/ψ$. Our results indicate that the polarization at high $p_T$ is similar to that observed in $pp$ collisions. However, at low $p_T$, where regenerated $J/ψ$ dominates, it is likely that the polarized charm quarks in the rotational QGP medium are responsible for this phenomenon. Our study supplies a baseline for future research on the effects of strong electromagnetic and vorticity fields on $J/ψ$ polarization.

hep-ph↗

arXiv2023

Machine learning approach to analyze heavy quark diffusion coefficient in relativistic heavy-ion collisions

The diffusion coefficient of heavy quarks in the deconfined medium is examined in this research using a deep convolutional neural network (CNN) trained with data from relativistic heavy ion collisions involving heavy flavor hadrons. The CNN is trained using observables such as the nuclear modification factor $R_{AA}$ and the elliptic flow $v_2$ of non-prompt $J/ψ$ from B-hadron decay in different centralities, where B meson evolutions are calculated using the Langevin equation and the Instantaneous Coalescence Model. The CNN outputs the parameters characterizing the temperature and momentum dependence of the heavy quark diffusion coefficient. By inputting the experimental data of non-prompt $J/ψ$ $(R_{AA}, v_2)$ from various collision centralities into multiple channels of the well-trained network, we derive the values of the diffusion coefficient parameters. Additionally, We evaluate the uncertainty in determining the diffusion coefficient by taking into account the uncertainties present in the experimental data $(R_{AA}, v_2)$, which serve as inputs to the deep neural network.

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arXiv2023

Bottom energy loss and non-prompt $J/ψ$ production in relativistic heavy ion collisions

We study the momentum and centrality dependence of the non-prompt $J/ψ$ nuclear modification factors ($R_{AA}$), which comes from the $B$ hadrons decay, in Pb-Pb collisions at the Large Hadron Collider. Bottom quarks are produced in the parton hard scatterings and suffer energy loss in the quark-gluon plasma and the hadronic gas, where the spatial and time evolution of the medium is described with the hydrodynamic equations. Medium-induced elastic scatterings and the radiation in bottom quarks are included in the energy loss of bottom quarks. The hadronization process of bottom quarks is described with the instantaneous coalescence model. After considering both cold and hot nuclear matter effects in Pb-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV, we calculated the $R_{AA}$ and also the elliptic flows of non-prompt $J/ψ$ from the decay of $B$ mesons at different centralities and transverse momentum bins. The $R_{AA}$ and $v_2$ of non-prompt $J/ψ$ sensitive to the hot medium reflect and centrality supply an opportunity to study the bottom quarks energy loss in the hot medium.

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arXiv2023

Charmonium transport in the high-$μ_B$ medium

We employ the transport model coupled with hydrodynamic equations to study the charmonium dissociation and regeneration in the quark-gluon plasma (QGP) with the large baryon chemical potential in Au-Au collisions at the energies of $\sqrt{s_{NN}}=$ ($39$, $14.5$, $7.7$) GeV. The baryon chemical potential $μ_B$ is encoded in both Debye mass characterizing the heavy-quark potential and also the equation of state (EoS) of the bulk medium respectively. After considering $μ_B$-corrections in both heavy quarkonium and the QGP medium, we calculate the nuclear modification factor $R_{AA}$ of charmonium. And find the $μ_B$ influence on charmonium production at $\sqrt{s_{NN}}$ = 39 and 14.5 GeV is negligible, while the $R_{AA}$ of charmonium is reduced considering $μ_B$ influence at $\sqrt{s_{NN}}=7.7$ GeV Au-Au collisions. It is crucial for studying charmonium production in low energy and also fixed-target heavy-ion collisions.

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arXiv2023

Bottomonium transport in p-Pb and Pb-Pb collisions at the LHC

We employ the Boltzmann transport model to study the sequential suppression pattern of $Υ(1S,2S,3S)$ states in both small (p-Pb) and the large (Pb-Pb) collision systems at $\sqrt{s_{NN}}=5.02$ TeV. The cold nuclear matter effects happen before the formation of bottomonium, which is the same for different bottomonium states $Υ(1S,2S,3S)$. The sequential suppression pattern of bottomonium states is treated as a signal of the hot medium effects, where bottomonium states suffer different magnitudes of the color screening and parton inelastic scatterings due to their different geometry sizes and binding energies. Bottomonium excited states are more easily dissociated with smaller binding energy via the final-state interactions. Including both cold and hot medium effects, transport model consistently explains the experimental data about bottomonium in both small and large collision systems.

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arXiv2023

Non-thermal distributions of charm and charmonium in relativistic heavy-ion collisions

We employ the Boltzmann transport model to study the charmonium regeneration with non-thermal charm quarks in relativistic heavy-ion collisions. As heavy quarks do not reach kinetic thermalization in the quark-gluon plasma (QGP), the final transverse momentum distribution of regenerated charmonium depends on the degree of charm quark kinetic thermalization. When the charm momentum distribution becomes harder, more charm quarks are distributed in the middle and high $p_T$, where the production of regenerated charmonium also becomes larger. With non-thermal momentum distribution of charm quarks in their coalescence process, the nuclear modification factor $R_{AA}(p_T)$ of charmonium enhances at middle $p_T$. Besides, the elliptic flow $v_2(p_T)$ of charmonium also enhances at middle $p_T$ as more regenerated charmonium are distributed in this $p_T$ region. The theoretical calculations with non-thermal charm distribution explain well the $p_T$ dependence of charmonium $R_{AA}$ and $v_2$, which indicates that charm quarks do not reach complete kinetic thermalization in the QGP when charmonium are regenerated.

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arXiv2023

Bottomonium sequential suppression and strong heavy-quark potential in heavy-ion collisions

We employ the time-dependent Schrödinger equation with different complex potentials to study the bottomonium sequential suppression in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV and 5.02 TeV and Au-Au collisions at $\sqrt{s_{NN}}=200$ GeV. Both color screening effect and the random scatterings with thermal partons are considered in the real and imaginary parts of the heavy-quark potentials. As the real part of the heavy-quark potential is between the free energy $F(T,r)$ and the internal energy $U(T,r)$ of heavy quarkonium, we parametrize different potentials with a function of $F$ and $U$ to evolve the bottomonium wave packages in the medium. We find that when the real part of the potential is close to $U(T,r)$, it can explain well the pattern of bottomonium sequential suppression where their nuclear modification factors satisfy the relation $R_{AA}(1s)>R_{AA}(2s)>R_{AA}(3s)$ observed in experiments. In the other limit of $F(T,r)$, bottomonium wave packages tend to expand due to weak attracted force, which results in evident transitions from $Υ(2s)$ to $Υ(3s)$ components and does not satisfy the sequential suppression pattern. We suggest that the bottomonium sequential suppression can be a probe of strong heavy-quark potential in the medium.

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arXiv2023

Searching for doubly charmed tetraquark candidates $T_{cc}$ and $T_{cc\bar{s}}$ in $B_c$ decays

In this work, we propose to search for the exotic doubly charmed meson $T_{cc}^+$ and its analog $T_{cc\bar{s}}^+$ in $B_c^+$ decays, which provide a good environment for the formation of the exotic state containing double charm quarks. Within the molecular scheme, the production of $T_{cc}^+$ and $T_{cc\bar{s}}^+$ through various rescattering processes with different intermediate states are investigated. For the moderate values of model parameters, the branching ratios of $B_c^+$ decaying into $T_{cc}^+ \bar{D}^{0}$, $T_{cc}^+ \bar{D}^{*0}$, $T_{cc\bar{s}}^+ \bar{D}^{0}$ and $T_{cc\bar{s}}^+ \bar{D}^{*0}$ are estimated to be of the order of $10^{-7}$, $10^{-5}$, $10^{-6}$ and $10^{-4}$, respectively, which may be tested by future experiments.

hep-ph↗

arXiv2022

Fourier-Flow model generating Feynman paths

As an alternative but unified and more fundamental description for quantum physics, Feynman path integrals generalize the classical action principle to a probabilistic perspective, under which the physical observables' estimation translates into a weighted sum over all possible paths. The underlying difficulty is to tackle the whole path manifold from finite samples that can effectively represent the Feynman propagator dictated probability distribution. Modern generative models in machine learning can handle learning and representing probability distribution with high computational efficiency. In this study, we propose a Fourier-flow generative model to simulate the Feynman propagator and generate paths for quantum systems. As demonstration, we validate the path generator on the harmonic and anharmonic oscillators. The latter is a double-well system without analytic solutions. To preserve the periodic condition for the system, the Fourier transformation is introduced into the flow model to approach a Matsubara representation. With this novel development, the ground-state wave function and low-lying energy levels are estimated accurately. Our method offers a new avenue to investigate quantum systems with machine learning assisted Feynman Path integral solving.

hep-lat↗

arXiv2022

Relativistic correction to the dissociation temperature of B_c mesons in the hot medium

By solving two body Dirac equations with potentials at finite temperature, we calculated the dissociation temperature T_d of B_c mesons in the quark-gluon plasma. It is found that the T_d becomes higher with the relativistic correction than the T_d from the Schroedinger equation. Both the short range interaction and the constant term of the potential at the long-range scale have a contribution to the shift of T_d, while the spin interaction is negligible.

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arXiv2022

Charmonium dissociation at high baryon chemical potential

We study the charmonium dissociation in the hot medium with finite baryon chemical potential $μ_B$. Charmonium bound states are dissociated in the medium by the color screening effect and the random scatterings with thermal partons, which are included in the real and imaginary parts of the potential respectively. $J/ψ$ fraction in the $c\bar c$ pair defined to be the quantum overlap between the wave package and the wave function of $J/ψ$ eigenstate decreases with time due to the complex potentials. When $μ_B$ is large compared with the medium temperature, the Deybe mass is increased evidently. We consider $μ_B$-dependent Deybe mass in both real and imaginary parts of the potential to calculate the $J/ψ$ survival probability in the static medium and the Bjorken medium. $J/ψ$ survival probability is reduced evidently by the $μ_B$ effect at low temperatures available in the medium produced in Beam Energy Scan experiments, while this effect becomes not apparent at high temperatures.

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arXiv2022

Anisotropic flows of charmonium in the relativistic heavy-ion collisions

We review recent studies about anisotropic flows ($v_1, v_2, v_3$) of charmonium in the quark-gluon plasma produced in relativistic heavy-ion collisions. Collective flows of the bulk medium are developed due to the anisotropic pressure gradient of the medium. Strongly coupled with the bulk medium, charm quarks carry collective flows from the expanding medium, which will be inherited by the regenerated charmonium via the coalescence process. In event-by-event collisions where nucleon positions fluctuate from the smooth distribution, there is triangularity in the medium initial energy density. Triangular flows of the bulk medium and heavy flavor particles can be developed due to the initial fluctuations. In the longitudinal direction, the rapidity-odd distribution of the initial energy density is induced by the rotation of the medium in non-central heavy-ion collisions. Charmonium suffers biased dissociation along positive and negative $x$-directions in forward (backward) rapidity. The directed flow of charmonium becomes non-zero. The directed, elliptic and triangular flows ($v_1, v_2, v_3$) of charmonium come from the anisotropic initial distributions of the medium energy density in the transverse and longitudinal directions.

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arXiv2022

$B_c^+$ Formation from Random Charm and Anti-bottom Quarks in the Quark-Gluon Plasma

We study the $B_c^+$ production in Pb-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV. In the quark-gluon plasma (QGP) produced in heavy-ion collisions, heavy quarks make random motions with the energy loss. We employ the Langevin equations to study the non-equilibrium distributions of heavy quarks and the Instantaneous Coalescence Model (ICM) to study the hadronization process. Due to abundant charm and bottom quarks in the QGP, their coalescence probability is significantly enhanced compared with the situations in proton-proton collisions. We find that the final production of $B_c^+$ is increased by the coalescence process, which makes the nuclear modification factor ($R_{AA}$) of $B_c^+$ larger than the unit. Our model explains the experimental data well at semi-central and central collisions. The observation of $R_{AA}(B_c^+)>1$ is regarded as an evident and strong signal of the existence of the deconfined medium generated in heavy-ion collisions.

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arXiv2022

Probe the color screening in proton-nucleus collisions with complex potentials

Color screening and parton inelastic scattering modify the heavy-quark antiquark potential in the medium that consists of particles from quantum chromodynamics (QCD), leading to suppression of quarkonium production in relativistic heavy-ion collisions. Due to small charm/anti-charm ($c\bar{c}$) pair production number in proton-nucleus (pA) collisions, the correlation between different $c\bar{c}$ pairs is negligible, which makes the Schrödinger equation viable for tracking the evolution of only one $c\bar{c}$ pair. We employ the time-dependent Schrödinger equation with in-medium $c\bar{c}$ potential to study the evolution of charmonium wave functions in the hydrodynamic like QCD medium produced in pA collisions. We explore different parametrizations of real and imaginary parts of $c\bar{c}$ potential and calculate the nuclear modification factors ($R_{\rm pA}$) of $J/ψ$ and $ψ(2S)$ in $\sqrt{s_{NN}}=5.02$ TeV energy p-Pb collisions at Large Hadron Collider (LHC). Comparing a strong and a weak screening scenario with experimental data in this approach, we arrive at the conclusion that the color screening is weak at temperature close to deconfined phase transition. Moreover, the imaginary part of the potential is crucial to describe the experimental data which is consistent with widely studied semi-classical approaches where the dissociation rates are essential.

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arXiv2022

X(3872) Production in Relativistic Heavy-Ion Collisions

Heavy-ion collisions provide a unique opportunity to study the nature of X(3872) compared with electron-positron and proton-proton (antiproton) collisions. We investigate the centrality and momentum dependence of X(3872) in heavy-ion collisions via the Langevin equation and instant coalescence model (LICM). When X(3872) is treated as a compact tetraquark state, the tetraquarks are produced via the coalescence of heavy and light quarks near the quantum chromodynamic (QCD) phase transition due to the restoration of the heavy quark potential at $T\rightarrow T_c$. In the molecular scenario, loosely bound X(3872) is produced via the coalescence of $D^0$-$\bar D^{*0}$ mesons in a hadronic medium after kinetic freeze-out. We employ the LICM to explain both $D^0$ and $J/ψ$ production as a benchmark. Then we give predictions regarding X(3872) production and the nuclear modification factor $R_{AA}^{X(3872)}$. We find that the total yield of tetraquark is several times larger than the molecular production in Pb-Pb collisions. Although the geometric size of the molecule is huge, the coalescence probability is small due to strict constraints on the relative momentum between $D^0$ and $\bar D^{*0}$ in the molecular Wigner function, which significantly suppresses the molecular yield.

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