arXiv subjects

Yu-Gang Ma

Publications and source records attributed to Yu-Gang Ma.

At least 73 records · Page 4Linked to original sources

arXiv2025

Information entropy for central $^{197}$Au+$^{197}$Au collisions with the ultrarelativistic quantum molecular dynamics model

This study investigates the multiplicity information entropy of hadrons, anti-hadrons, baryons, and net-protons in central $^{197}$Au+$^{197}$Au collisions with impact parameters of 0$-$3 fm, using the ultrarelativistic quantum molecular dynamics model (UrQMD) across various center-of-mass energies ($\sqrt{s_{\rm NN}}$) from 5.0 to 54.4 GeV. Our simulations employ hydrodynamic modes with different equations of state (EoS) and a default mode without hydrodynamics. The results reveal that the information entropies of baryons and net-protons are sensitive to the selected EoS. In particular, enhancements of the information entropies around $\sqrt{s_{\rm NN}} \sim 30$ GeV, especially with chiral hadron gas and Bag model EoS, indicate a phase transition or critical endpoint behavior. These findings highlight the importance of the EoS in understanding the thermodynamic properties of matter produced in high-energy collisions.

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arXiv2025

Investigating the pion emission source in pp collisions using the AMPT model with sub-nucleon structure

The measurement of momentum correlations of identical pions serves as a fundamental tool for probing the space-time properties of the particle emitting source created in high-energy collisions. Recent experimental results have shown that, in pp collisions, the size of the one-dimensional primordial source depends on the transverse mass (\mt) of hadron pairs, following a common scaling behavior, similar to that observed in Pb--Pb collisions. In this work, a systematic study of the \pipi source function and correlation function is performed using the multiphase transport model (AMPT) to understand the properties of the emitting source created in high multiplicity pp collisions at $\sqrt{s}=13$ TeV. The \mt scaling behavior and pion emission source radii measured by ALICE experiment can be well described the model with sub-nucleon structure. These studies shed new light on the understanding of the effective size of the \pipi emission source and on studying the intensity interferometry in small systems with a transport model.

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arXiv2025

The 3$α$ correlations of ground and excited $0^+$ states of $^{12}\mathrm{C}$ within the microscopic cluster model

The cluster structures of the $0^+$ states in $^{12}\mathrm{C}$, including the ground state, the Hoyle state, and the recently identified $0_3^+$ and $0_4^+$ states, are analyzed to explore the cluster configurations and $3α$ correlations without assuming the existence of $^8\mathrm{Be}$. In particular, the key quantity -- two-cluster overlap amplitudes -- is calculated for the $3α$ clustering channels to reveal the essential features of these $0^+$ states. The results clearly show the distinction between the compact structure of the ground state and the gas-like structures of the excited $0^+$ states. The Hoyle state exhibits the expected gas-like dominant ($0S$) configuration, while the $0_3^+$ state shows a more extended $3α$ clustering structure, which can be viewed as a breathing-like excitation of the Hoyle state, with an additional nodal structure. The $0_4^+$ state is found to have a mixed configuration, featuring a bent-arm-like structure in the $S\otimes S$ channel and an enhanced $2α$ correlation in the $D\otimes D$ channel.

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arXiv2025

Deciphering Hypertriton and Antihypertriton Spins from Their Global Polarizations in Heavy-Ion Collisions

Understanding the properties of hypernuclei is crucial for constraining the nature of hyperon-nucleon ($Y\text{-}N$) interactions, which plays a key role in determining the inner structure of compact stars. The lightest hypernuclei and antihypernuclei are the hypertriton ($^3_Λ\text{H}$), which consists of a pair of nucleons and a $Λ$ hyperon, and its antinucleus (${^3_{\barΛ}}\overline{\rm H}$). Significant knowledge has recently been acquired regarding the mass, lifetime, and binding energy of $^3_Λ\text{H}$. However, its exact spin, whether $\frac{1}{2}$ or $\frac{3}{2}$, remains undetermined in both experimental and theoretical studies. Here, we present a novel method of using the hypertriton global polarization in heavy-ion collisions to decipher not only its total spin but also its internal spin structure. This method is based on the finding that its three different spin structures exhibit distinct beam energy dependence of its global polarization when it is produced in these collisions from the coalescence of proton, neutron and $Λ$. Future observations of the hypertriton and antihypertriton global polarizations thus provide the opportunity to unveil the spin structures of hypertriton and antihypertriton and their production mechanisms in heavy-ion collisions.

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arXiv2025

Analysis of clustering fragments of $^7$Li and $^7$Be in the microscopic cluster model

The nuclear structures of $^7$Li($α+n+n+p$) and $^7$Be($α+p+p+n$) are studied within the microscopic cluster model, in which the clustering fragments e.g., triton, $^3$He, and even the single nucleons around the core are studied in the $^7$Li and $^7$Be systems. We obtain the energy spectra and wave functions of $^7$Li and $^7$Be, and the calculated energy spectra of the ground states and some of the excited states are consistent with experimental data. To investigate the cluster-formation probabilities, we calculate the reduced-width amplitudes of various binary partitions. The results show that the $α+t(^3\mathrm{He})$ cluster structure is dominant in the low-lying states of $^7$Li($^7$Be), including the ground state and the three lowest excited states. In some higher states around the single-particle thresholds, the components of $\mathrm{core}+N$ structures, namely $^6\mathrm{Li}+n$ and $^6\mathrm{He}+p$ in $^7$Li and $^6\mathrm{Li}+p$ in $^7$Be, are significantly enhanced.

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arXiv2025

Probing Nuclear Excitation by Electron Capture in an Electron Beam Ion Trap with Non-destructive Isomer Detection via Precision Mass Spectrometry

Nuclear excitation by electron capture (NEEC) is an important nuclear excitation mechanism which still lacks conclusive experimental verification. This is primarily attributed to strong background x-/$γ$-ray noise and competing nuclear excitation processes which would overshadow the signals in various environments that NEEC takes place. Here, we propose an experimental approach to observe the NEEC process within a background-free environment. Through collisions with a highly-compressed mono-energetic electron beam in an electron beam ion trap, nuclei may get excited to a long-lived isomeric state via the NEEC process. Subsequently, ions can be extracted and Penning-trap mass spectrometry employed to unambiguously detect the isomer. Our study focuses on the promising candidate $^{189}\mathrm{Os}$, demonstrating measurable detection rates of the NEEC process and discussing the feasibility of the proposed approach. This new approach for observing the NEEC process may be realized in the near future.

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arXiv2024

Production of exotic hadrons in $pp$ and nuclear collisions

Exotic hadrons beyond the conventional quark model have been discovered in the past two decades. Investigations of these states can lead to deep understanding of nonperturbative dynamics of the strong interaction. In this concise review, we focus on the productions of exotic hadrons in $pp$, $p\bar p$, and nuclear collisions. Experimental observations of light nuclei and hypernuclei, as prototypes of hadronic molecules, in heavy ion collisions will also be briefly discussed.

hep-ph↗

arXiv2024

Activation of momentum fluctuations in wave packet molecular dynamics: Impacts on momentum distributions of projectilelike fragments

Molecular dynamics approaches use wave packets as nucleon wave functions to simulate the time evolution of nuclear reactions. It is crucial to activate the momentum fluctuation inherent in each wave packet so that it properly affects the time evolution. In the antisymmetrized molecular dynamics (AMD) model, this has traditionally been done by splitting the wave packets, i.e., by introducing a random fluctuation to the wave packet center of each particle. The present work proposes an improved approach to activate the fluctuation in both the one-body mean-field propagation and the two-nucleon collision processes, consistently based on the gradual or sudden change of the degree of isolation, which is derived from the fragment number function used for the zero-point energy subtraction. This new method is applied to the 12C + 12C and 12C + p reactions at about 100 MeV/nucleon, focusing on the momentum distribution of the 11B fragments produced by one-proton removal from the 12C projectile. The results show that, with the momentum fluctuation suitably activated, the method correctly accounts for the recoil from the removed nucleon to the residue and the 11B momentum distribution is significantly improved, while without activating the fluctuation the distribution is too narrow compared to the experimental data. Furthermore, the AMD results indicate that the momentum distribution consists of two components; one is the high $P_z$ component with a small shift from the beam velocity, resulting from the simple removal of a proton after an energetic collision with a target particle; the other is the low $P_z$ component with a larger peak shift resulting from the decay of an excited 12C nucleus in a longer time scale. The activation of momentum fluctuation mainly affects the high $P_z$ component to broaden it. The role of cluster correlations in this problem is also investigated.

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arXiv2024

A Novel Framework for Characterizing Spacetime Microstructure with Scaling

The study of physics at the Planck scale has garnered significant attention due to its implications for understanding the fundamental nature of the universe. At the Planck scale, quantum fluctuations challenge the classical notion of spacetime as a smooth continuum, revealing a complex microstructure that defies traditional models. This study introduces a novel scaling-based framework to investigate the properties of spacetime microstructures. By deriving a scaling-characterized metric tensor and reformulating fundamental equations--including the geodesic, Einstein field, Klein-Gordon, and Dirac equation--into scaling forms, the research reveals new properties of local spacetime dynamics. Remarkably, the golden ratio emerges naturally in linear scale measurements, offering a potential explanation for the role of the Planck length in resolving ultraviolet (UV) divergence. Furthermore, the study demonstrates how scale invariance in spacetime can restore classical geometric stability through the renormalization group equations. These findings significantly revise classical geometric intuitions, providing a fresh lens for understanding quantum fluctuations and offering promising insights for advancing quantum gravity theories.

gr-qc↗

arXiv2024

Exploring the Diversity of Nuclear Density through Information Entropy

This study explores the role of information entropy in understanding nuclear density distributions, including both stable configurations and non-traditional structures such as neutron halos and $α$-clustering. By quantifying the uncertainty and disorder inherent in nucleon distributions in nuclear many-body systems, information entropy provides a macroscopic measure of the physical properties of the system. A more dispersed and disordered density distribution results in a higher value of information entropy. This intrinsic relationship between information entropy and system complexity allows us to quantify uncertainty and disorder in nuclear structures by analyzing various geometric parameters such as nuclear radius, diffuseness, neutron skin, and cluster structural features.

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arXiv2024

Properties of the QCD Matter: A Review of Selected Results from the ALICE Experiment

The Large Hadron Collider (LHC), the world's largest and most powerful particle accelerator, has been a pivotal tool in advancing our understanding of fundamental physics. By colliding heavy ions (such as lead ions), the LHC recreates conditions similar to those just after the Big Bang. This allows scientists to study the Quark-Gluon Plasma (QGP), a state of matter where quarks and gluons are not confined within protons and neutrons. These studies provide insights into the strong force and the early universe's behavior. In this paper, we provide a comprehensive overview of recent significant findings from A Large Ion Collider Experiment (ALICE) at LHC. The topics encompass measurements regarding to properties of the QGP, particle production, flow and correlations, dileptons, quarkonia and electromagnetic probes, heavy flavor, and jets. Additionally, we introduce future plans for detector upgrades of the ALICE experiment.

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arXiv2024

Vector meson's spin alignments in high energy reactions

The global spin alignment of vector mesons has been observed by the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). It provides a unique opportunity to probe the correlation between the polarized quark and antiquark in the strongly coupled quark-gluon plasma (sQGP) produced in relativistic heavy ion collisions, opening a new window to explore the properties of sQGP. In addition, spin alignments of vector mesons have also been observed in other high-energy particle collisions such as $e^+e^-$ annihilations at high energies where hadron production is dominated by quark fragmentation mechanism. The results obtained are quite different from those obtained in heavy ion collisions where quark coalescence/combination mechanism dominates suggesting strong dependence on hadronization mechanisms. So comprehensive studies in different hadronization processes are needed. In this article, we present a brief review of theoretical and experimental advances in the study of vector meson's spin alignments in a variety of high-energy particle collisions, with emphasis on hadronization mechanisms.

hep-ph↗

arXiv2024

Neutron skin and its effects in heavy-ion collisions

Neutron skin is an exotic phenomena in unstable nuclei. The various effects in nuclear reactions caused by the neutron skin and also its relation with the properties of nuclear structure are reviewed in this article. Based on numerous studies with theoretical models, strong correlations have been found between the neutron skin thickness and neutron removal cross section, neutron/proton yield ratio, t/\ch{^3He} yield ratio, neutron-proton momentum difference, isoscaling parameter, photon production, reaction cross sections for neutron induced reactions, charge-changing cross sections difference of mirror nuclei, astrophysical $S$-factor, and other quantities in nuclear reactions induced by neutron-rich nuclei. Moreover, the relationships between neutron skin thickness and some properties of nuclear structure, such as $α$-cluster formation, $α$ decay, nuclear surface, nuclear temperature, and proton radii difference of mirror nuclei, have also been investigated. It also has been shown that the neutron skin plays a crucial role in relativistic heavy-ion collisions. Experimentally, an unstable nucleus with neutron skin can be generated by radioactive nuclear beam facilities, and the thickness of neutron skin could be extracted by measuring the sensitive probes, which further helps giving stringent constraints on the equation of state of asymmetric nuclear matter and properties of neutron stars.

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arXiv2024

Bubble $^{36}$Ar and Its New Breathing Modes

The bubble nuclei are important components of exotic nuclear structures characterized by special depletions of central densities. Focusing on bubble structures of $^{36}$Ar, the characterizations of bubble nuclei were explored with the framework of the extended quantum molecular dynamics model. Three density distribution modes were uncovered for the first time, i.e. micro-bubble, bubble, and cluster resonances, which show unique spectral signature compared to the monopole resonance spectrum as the excitation intensity was increased in bubbles. Of pivotal importance is the revelation that the bubble mode's oscillation frequency closely resembles macroscopic bubble dynamics, building a connection between classical macroscopic phenomena and the quantum complexity of the nuclear structure. The discovery marks a crucial step forward in deciphering the relationship between classical and quantum domains within the enigmatic world of atomic nuclei.

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arXiv2024

Jet-Induced Enhancement of Deuteron Production in $pp$ and $p$-Pb Collisions at the LHC

Jet-associated deuteron production in $pp$ collisions at $\sqrt{s}=13$ TeV and $p$-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV is studied in the coalescence model by using the phase-space information of proton and neutron pairs from a multiphase transport (AMPT) model at the kinetic freezeout. In the low transverse momentum ($p_T$) region $p_T/A < 1.5$ GeV/$c$, where $A$ is the mass number of a nucleus, the in-jet coalescence factor $B_2^\text{In-jet}$ for deuteron production, given by the ratio of the in-jet deuteron number to the square of the in-jet proton number, is found to be larger than the coalescence factor $B_2$ in the medium perpendicular to the jet by a factor of about 10 in $pp$ collisions and of 25 in $p-$Pb collisions, which are consistent with the ALICE measurements at the LHC. Such large low-momentum enhancements mainly come from coalescence of nucleons inside the jet with the medium nucleons. Coalescence of nucleons inside the jet dominates deuteron production only at the higher $p_T$ region of $p_T/A\gtrsim 4$ GeV/$c$, where both the yield ratio $d/p$ of deuteron to proton numbers and the $B_2$ are also significantly larger in the jet direction than in the direction perpendicular to the jet due to the strong collinear correlation among particles produced from jet fragmentation. Studying jet-associated deuteron production in relativistic nuclear collisions thus opens up a new window to probe the phase-space structure of nucleons inside jets.

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arXiv2024

Softening of the Hypertriton Transverse Momentum Spectrum in Heavy-Ion Collisions

Understanding the properties of hypernuclei helps to constrain the interaction between hyperon and nucleon, which is known to play an essential role in determining the properties of neutron stars. Experimental measurements have suggested that the hypertriton ($^3_Λ\text{H}$), the lightest hypernucleus, exhibits a halo structure with a deuteron core encircled by a $Λ$ hyperon at a distance of about 10 fm. This large $Λ-d$ distance in $^3_Λ\text{H}$ wave function is found to cause a suppressed $^3_Λ\text{H}$ yield and a softening of its transverse momentum ($p_T$) spectrum in relativistic heavy-ion collisions. Within the coalescence model based on nucleons and $Λ$ hyperons from a microscopic hybrid hydro model with a hadronic afterburner for nuclear cluster production in Pb-Pb collisions at $\sqrt{s_{NN}}$= 5.02 TeV, we show how this softening of the hypertriton $p_T$ spectrum appears and leads to a smaller mean $p_T$ for $^3_Λ\text{H}$ than for helium-3 ($^3$He). The latter is opposite to the predictions from the blast-wave model which assumes that $^3_Λ\text{H}$ and $^3$He are thermally produced at the kinetic freeze-out of heavy-ion collisions. The discovered quantum mechanical softening of the (anti-)hypertriton spectrum can be experimentally tested in relativistic heavy-ion collisions at different collision energies and centralities and used to obtain valuable insights into the mechanisms for light (hyper-)nuclei production in these collisions.

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arXiv2024

Properties of the QCD Matter -- An Experimental Review of Selected Results from RHIC BES Program

In the paper, we discuss the development of the multi-gap resistive plate chamber Time-of-Flight (TOF) technology and the production of the STAR TOF detector in China at the beginning of the 21st century. Then we review recent experimental results from the first beam energy scan program (BES-I) at the Relativistic Heavy Ion Collider (RHIC). Topics cover measurements of collectivity, chirality, criticality, global polarization, strangeness, heavy-flavor, di-lepton and light nuclei productions.

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arXiv2024

Electromagnetic fields in ultra-peripheral relativistic heavy-ion collisions

Ultraperipheral heavy-ion collisions (UPCs) offer unique opportunities to study processes under strong electromagnetic fields. In these collisions, highly charged fast-moving ions carry strong electromagnetic fields that can be effectively treated as photon fluxes. The exchange of photons can induce photonuclear and two-photon interactions, and excite ions. This excitation of the ions results in Coulomb dissociation with the emission of photons, neutrons, and other particles. Additionally, the electromagnetic fields generated by the ions can be sufficiently strong to enforce mutual interactions between the two colliding ions. Consequently, the two colliding ions experienced an electromagnetic force that pushed them in opposite directions, causing a back-to-back correlation in the emitted neutrons. Using a Monte Carlo simulation, we qualitatively demonstrated that the above electromagnetic effect is large enough to be observed in UPCs, which would provide a clear means to study strong electromagnetic fields and their effects.

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