Nuclear Theory·nucl-th

Tue·Sep 8, 2020Tuesday·September 8, 2020

16 papers—5 primary·11 cross-listed

01
Constraints on jet quenching from a multi-stage energy-loss approach
C. Park🇨🇦 · A. Angerami🇺🇸 · S. A. Bass🇺🇸 · S. Cao🇺🇸 · Y. Chen🇺🇸 · J. Coleman🇺🇸 · L. Cunqueiro🇺🇸 · T. Dai🇺🇸 · L. Du🇺🇸 · R. Ehlers🇺🇸 · H. Elfner🇩🇪 · D. Everett🇺🇸 and 38 other authors
We present a multi-stage model for jet evolution through a quark-gluon plasma within the JETSCAPE framework. The multi-stage approach in JETSCAPE provides a unified description of distinct phases in jet shower contingent on the virtuality. We demonstrate a simultaneous description of leading hadron and integrated jet observables as well as jet $v_{n}$ using tuned parameters. Medium response to the jet quenching is implemented based on a weakly-coupled recoil prescription. We also explore the cone-size dependence of jet energy loss inside the plasma.
nucl-thhep-exhep-phPoS(2021)·3 citations
02
Directed flow induced by electromagnetic fields in heavy ion collisions
Yifeng Sun🇮🇹 · Salvatore Plumari🇮🇹 · Vincenzo Greco🇮🇹
Strong electromagnetic fields are expected to be generated in off-central relativistic heavy ion collisions, which can induce a splitting of the directed flow of charged particles and anti-particles ( $Δ v_{1}$ ). Such a splitting manifests even for neutral charmed mesons pairs ( $D^{0}, D ˉ^{0}$ ), hence being a direct probe of the formation of deconfined phase with charm quarks as degree of freedom. In the limit of large $p_{T}$ and weak interaction with the QGP, a formula of $Δ v_{1} (p_{T}, y_{z})$ of charged particles and anti-particles as a function of $p_{T}$ and rapidity $y_{z}$ can be obtained, which is found to be related to the spectra of charged particles and the integrated effect of the Lorentz force. This formula is expected to be valid to heavy quarks and leptons at high $p_{T}$ , where the modification to their equations of motion due to the interaction with both QGP and electromagnetic fields is small, and should have a general application. We also proposed a measurement of $Δ v_{1} (p_{T}, y_{z})$ of leptons from $Z^{0}$ decay and its correlation to that of $D$ mesons, which would be a strong probe determining whether the large splitting measured in experiments has the electromagnetic origin.
nucl-thhep-exhep-phPoS(2021)·2 citations
03
Pion production and absorption in heavy-ion collisions
Yuan Gao · Lei Zhang · Gao-Chan Yong · Zi-Yu Liu · Wei Zuo
Based on the isospin dependent transport model IBUU, the pion production and its absorption are thoroughly studied in the central collision of $A u + A u$ at a beam energy of 400 MeV/nucleon. It is found that the pions are firstly produced by the hard $Δ$ decay at the average density around $1.75 ρ_{0}$ , whereas about 18\% of them are absorbed absolutely in the subsequent inelastic collisions. For the free pions observed, more than half of them have been scattered for one or more times before they are free from matter. And the more scattering numbers of pions, the higher the momentum they possess. These pions, due to longer time of their existence in high density nuclear matter, carry more information about the symmetry energy of the nuclear matter at high densities.
nucl-thPRC(2021)·5 citations
04
Identifying the nature of the QCD transition in heavy-ion collisions with deep learning
Yi-Lun Du🇳🇴 · Kai Zhou🇩🇪 · Jan Steinheimer🇩🇪 · Long-Gang Pang🇨🇳 · Anton Motornenko🇩🇪 · Hong-Shi Zong🇨🇳 · Xin-Nian Wang🇨🇳 · Horst Stoecker🇩🇪
In this proceeding, we review our recent work using deep convolutional neural network (CNN) to identify the nature of the QCD transition in a hybrid modeling of heavy-ion collisions. Within this hybrid model, a viscous hydrodynamic model is coupled with a hadronic cascade "after-burner". As a binary classification setup, we employ two different types of equations of state (EoS) of the hot medium in the hydrodynamic evolution. The resulting final-state pion spectra in the transverse momentum and azimuthal angle plane are fed to the neural network as the input data in order to distinguish different EoS. To probe the effects of the fluctuations in the event-by-event spectra, we explore different scenarios for the input data and make a comparison in a systematic way. We observe a clear hierarchy in the predictive power when the network is fed with the event-by-event, cascade-coarse-grained and event-fine-averaged spectra. The carefully-trained neural network can extract high-level features from pion spectra to identify the nature of the QCD transition in a realistic simulation scenario.
nucl-thhep-phNPA(2021)·5 citations
05
The alternating-parity bands of \element{236,238}{U} and \element{238,240}{Pu} in a particle-number conserving method based on cranked shell model
Xiao-Tao He🇨🇳 · Yu-Chun Li
The particle-number conserving (PNC) method in the framework of cranked shell model (CSM) is developed to deal with the reflection-asymmetric nuclear system by applying the $S_{x}$ symmetry. Based on an octupole-deformed Nilsson potential, the alternating-parity bands in \element{236,238}{U} and \element{238,240}{Pu} are investigated. The experimental kinematic moments of inertia (MoI) and the angular momentum alignments of all studied bands are reproduced well in the PNC-CSM calculations. The striking difference of rotational behaviors between U and Pu isotopes can be linked to the strength of octupole correlations. The upbendings of the alternating-parity bands in\element{236,238}{U} are due to the alignments of pairs of nucleons occupying $ν g_{9/2}$ , $π f_{7/2}$ orbitals and $ν j_{15/2}$ , $π i_{13/2}$ high- $j$ intruder orbitals. Particularly, the interference terms of nucleon occupying the octupole-correlation pairs of $ν^{2} j_{15/2} g_{9/2}$ and of $π^{2} i_{13/2} f_{7/2}$ give a very important contribution to the suddenly gained alignments.
nucl-thnucl-exPRC(2020)·13 citations
06
Resummed Gluon Propagator and Debye Screening Effect in a Holonomous Plasma
Yun Guo🇨🇳 · Zhenpeng Kuang🇨🇳
Based on the Dyson-Schwinger equation, we compute the resummed gluon propagator in a holonomous plasma that is described by introducing a constant background field for the vector potential $A_{0}$ . Due to the transversality of the holonomous Hard-Thermal-Loop in gluon self-energy, the resummed propagator has a similar Lorentz structure as that in the perturbative Quark-Gluon Plasma where the holonomy vanishes. As for the color structures, since diagonal gluons are mixed in the over-complete double line basis, only the propagators for off-diagonal gluons can be obtained unambiguously. On the other hand, multiplied by a projection operator, the propagators for diagonal gluons, which exhibit a highly non-trivial dependence on the background field, are uniquely determined after summing over the color indices. As an application of these results, we consider the Debye screening effect on the in-medium binding of quarkonium states by analyzing the static limit of the resummed gluon propagator. In general, introducing non-zero holonomy merely amounts to modifications on the perturbative screening mass $m_{D}$ and the resulting heavy-quark potential, which remains the standard Debye screened form, is always deeper than the screened potential in the perturbative Quark-Gluon Plasma. Therefore, a weaker screening, thus a more tightly bounded quarkonium state can be expected in a holonomous plasma. In addition, both the diagonal and off-diagonal gluons become distinguishable by their modified screening masses $M_{D}$ and the temperature dependence of the ratio $M_{D} / T$ shows a very similar behavior as that found in lattice simulations.
↳ hep-phhep-thnucl-thPRD(2021)·9 citations
07
Quarkonium Semiclassical Transport in Quark-Gluon Plasma: Factorization and Quantum Correction
Xiaojun Yao🇺🇸 · Thomas Mehen🇺🇸
We study quarkonium transport in the quark-gluon plasma by using the potential nonrelativistic QCD (pNRQCD) effective field theory and the framework of open quantum systems. We argue that the coupling between quarkonium and the thermal bath is weak using separation of scales, so the initial density matrix of the total system factorizes and the time evolution of the subsystem is Markovian. We derive the semiclassical Boltzmann equation for quarkonium by applying a Wigner transform to the Lindblad equation and carrying out a semiclassical expansion. We resum relevant interactions to all orders in the coupling constant at leading power of the nonrelativistic and multipole expansions. The derivation is valid for both weakly coupled and strongly coupled quark-gluon plasmas. We find reaction rates in the transport equation factorize into a quarkonium dipole transition function and a chromoelectric gluon distribution function. For the differential reaction rate, the definition of the momentum dependent chromoelectric gluon distribution function involves staple-shaped Wilson lines. For the inclusive reaction rate, the Wilson lines collapse into a straight line along the real time axis and the distribution becomes momentum independent. The relation between the two Wilson lines is analogous to the relation between the Wilson lines appearing in the gluon parton distribution function (PDF) and the gluon transverse momentum dependent parton distribution function (TMDPDF). The centrality dependence of the quarkonium nuclear modification factor measured by experiments probes the momentum independent distribution while the transverse momentum dependence and measurements of the azimuthal angular anisotropy may be able to probe the momentum dependent one. We discuss one way to indirectly constrain the quarkonium in-medium real potential by using the factorization formula and lattice calculations. The leading quantum correction to the semiclassical transport equation of quarkonium is also worked out. The study can be easily generalized to quarkonium transport in cold nuclear matter, which is relevant for quarkonium production in eA collisions in the future Electron-Ion Collider.
↳ hep-phnucl-thJHEP(2021)·74 citations
08
Investigation of the elliptic flow fluctuations of the identified particles using the A Multi-Phase Transport model
Niseem Magdy🇺🇸 · Xu Sun🇺🇸 · Zhenyu Ye🇺🇸 · Olga Evdokimov🇺🇸 · Roy A. Lacey🇺🇸
A Multi-Phase Transport (AMPT) model is used to study the elliptic flow fluctuations of identified particles using participant and spectator event planes. The elliptic flow measured using the first order spectator event plane is expected to give the elliptic flow relative to the true reaction plane which suppresses the flow fluctuations. However, the elliptic flow measured using the second-order participant plane is expected to capture the elliptic flow fluctuations. Our study shows that the first order spectator event plane could be used to study the elliptic flow fluctuations of the identified particles in the AMPT model. The elliptic flow fluctuations magnitude shows weak particle species dependence and transverse momentum dependence. Such observation will have important implications for understanding the source of the elliptic flow fluctuations.
↳ nucl-exnucl-thUniverse(2020)·17 citations
09
Measurements of heavy-flavor jets with ALICE at the LHC
Ashik Ikbal Sheikh (for the ALICE Collaboration)🇮🇳
Heavy quarks created in ultra-relativistic heavy-ion collisions are mostly produced in hard QCD processes during the early stages of the reaction. They interact with the hot and cold nuclear matter throughout the evolution of the medium via semi-hard and soft processes such as energy loss via gluon radiations and collisions. Nuclear modification of heavy flavors in p-A systems provides insight into cold nuclear matter effects such as (anti)shadowing and $k_{T}$ -broadening, and serves as a baseline for A-A studies. In addition to that the fully reconstructed heavy-flavor jets provide additional information on the flavor (or mass) dependence of fragmentation, color charge effects as well as insight into the contribution of late gluon splitting. In this contribution, we present the measurements of $b$ -jet production in p-Pb collisions at $s_{NN} = 5.02$ TeV and $c$ -jet production in pp, p-Pb and Pb-Pb collisions measured by the ALICE experiment at the LHC. The measurements of the nuclear modification factors for $c$ -jet in p-Pb and Pb-Pb collisions are also presented. The experimental measurements are compared with the results from Monte Carlo event generators (PYTHIA 6, PYTHIA 8 and Herwig 7) and the NLO pQCD calculations (POWHEG+PYTHIA6). We find good agreement of the measurements with the results from Monte Carlo event generators and from NLO pQCD calculations.
↳ nucl-exhep-phnucl-thNucl.Part.Phys.Proc.(2020)·3 citations
10
Measurements of $^{na t} P b (p, x n)^{201 - 207} B i$ , $^{204} P b (p, 1 - 4 n)^{201 - 204} B i$ and $^{206} P b (p, 3 n)^{204} B i$ cross-sections at astrophysical energies ( $E_{p} \leq 30 M e V$ )
P V Guillaumon🇮🇹 · I D Goldman🇮🇱 · V R Vanin · H Barcellos de Oliveira
Cross-sections for $^{na t} P b (p, x n)^{201 - 207} B i$ , $^{204} P b (p, 1 - 4 n)^{201 - 204} B i$ and $^{206} P b (p, 3 n)^{204} B i$ reactions have been determined in the astrophysical energy range $20 - 30 M e V$ . The analysis were performed by $γ$ -spectroscopy associated with half-lives measurements. The results were compared with previously experimental data, when available, and with theoretical calculations performed using TALYS code. We report a possible new $γ$ transition from $^{204 m} P b$ and other theoretical discrepancies, probably due overestimation of the Coulomb barrier and neutron binding energy. Also reported are new determinations of the energies and intensities of the $γ$ 's emitted in the decays of $^{205, 206} B i$ . We discuss possible implications for the r/rp-processes in neutrino-driven wind in supernovae and neutron stars mergers.
↳ nucl-exnucl-th0 citations
11
QCD vacuum and baryon masses
Youngman Kim🇰🇷 · Igor A. Mazur🇰🇷 · Masayasu Harada🇯🇵 · Hyun Kyu Lee🇰🇷
To study a possible role of the quantum chromodynamics (QCD) vacuum in nuclear and hadron physics, we evaluate a physical quantity in a candidate of the QCD vacuum. In this study we adopt the Copenhagen (spaghetti) picture of the QCD vacuum and calculate the ground-state baryon masses in a constituent quark model. We find that the calculated baryon mass does depend on a parameter that characterizes the Copenhagen picture of the QCD vacuum and satisfies the Gell-Mann-Okubo mass relation for the baryon octet. We also observe that the effective constituent quark mass defined in this study contains a contribution attributed to the Copenhagen vacuum, that is the gluon background field. We then estimate the value of the background gluon field as a function of the up (down) constituent quark mass by using the baryon masses as inputs.
↳ hep-phnucl-thIJMPE(2023)·1 citation
12
Resolving the spacetime structure of jets with medium
Adam Takacs🇳🇴 · Daniel Pablos🇳🇴 · Konrad Tywoniuk🇳🇴
Away from the strictly soft and collinear limit of QCD radiation the choice of evolution scale in a parton shower algorithm is ambiguous and several options have been implemented in existing Monte Carlo event generators for proton-proton collisions. However, the resulting space-time evolution could result in subtle differences depending on the particular choice. In this work we quantify measurable consequences of the choice of the evolution variable and show how the implications of such a choice propagates into jet quenching observables. We develop a parton shower algorithm for a general evolution variable, that includes as special cases the virtuality, angle, transverse momentum and formation time. We study the interplay between the shower history for different evolution variables and the phase space affected by parton energy loss. In particular, we implement effects of jet quenching in the dense limit and highlight the role of color coherence effects. We compare the results of the different ordering variables to existing Monte Carlo shower implementations on the parton level by analyzing primary Lund planes. Finally, we study the sensitivity of quenched jets to the choice of evolution variable by confronting our results for a certain key observable, such as the jet mass.
↳ hep-phhep-exnucl-thPoS(2021)·1 citation
13
Energy loss and equilibration of jets in a QCD plasma
Soeren Schlichting🇩🇪 · Ismail Soudi🇩🇪
We investigate the medium induced fragmentation of jets in a high-temperature QCD plasma. Based on an effective kinetic theory of QCD, we study the non-equilibrium evolution of the jet shower and the chemical equilibration of jet fragments in the medium. By including radiative emissions as well as elastic interactions, our approach extends all the way from the jet energy scale to the temperature of the medium and includes important effects such as the recoil of the medium. We present results for the in-medium fragmentation, including chemical and kinetic equilibration of the soft fragments and discuss implications of our result to jet quenching physics and the problem of thermalization of the quark-gluon plasma in heavy ion collisions.
↳ hep-phnucl-thPoS(2021)·1 citation
14
Little-Bang and Femto-Nova in Nucleus-Nucleus Collisions
Kenji Fukushima🇯🇵 · Bedangadas Mohanty🇮🇳 · Nu Xu🇺🇸
We make a theoretical and experimental summary of the state-of-the-art status of hot and dense QCD matter studies on selected topics. We review the Beam Energy Scan program for the QCD phase diagram and present the current status of search for QCD Critical Point, particle production in high baryon density region, hypernuclei production, and global polarization effects in nucleus-nucleus collisions. The available experimental data in the strangeness sector suggests that a grand canonical approach in thermal model at high collision energy makes a transition to the canonical ensemble behavior at low energy. We further discuss future prospects of nuclear collisions to probe properties of baryon-rich matter. Creation of a quark-gluon plasma at high temperature and low baryon density has been called the "Little-Bang" and, analogously, a femtometer-scale explosion of baryon-rich matter at lower collision energy could be called the "Femto-Nova", which may possibly sustain substantial vorticity and magnetic field for non-head-on collisions.
↳ hep-phhep-exnucl-thAAPPS Bull.(2021)·52 citations
15
Dielectric Skyrmions
Sven Bjarke Gudnason🇨🇳
We consider the dielectric Skyrme model proposed recently, with and without the addition of the standard pion mass term. Then we write down Bogomol'nyi-type energy bounds for both the massless and massive cases. We further show that, except for when taking the strict BPS limit, the Skyrmions are made of 3 orthogonal dipoles that can always be placed in their attractive channel and form bound states. Finally, we study the model numerically and discover that, long before realistic binding energies are reached, the Skyrmions become bound states of well-separated point-particle-like Skyrmions. By going sufficiently close to the BPS limit, we are able to obtain classical binding energies of realistic values compared with experiments.
↳ hep-thhep-phnucl-thPRD(2020)·10 citations
16
Chiral phase transition and kaon-to-pion ratios in the entanglement SU(3) PNJL model
D. Blaschke🇵🇱 · A.V. Friesen🇷🇺 · Yu.L. Kalinovsky🇷🇺 · A. Radzhabov🇷🇺
Within the three-flavor PNJL and EPNJL chiral quark models we have obtained pseudoscalar meson properties in quark matter at finite temperature $T$ and baryochemical potential $μ_{B}$ . We compare the meson pole (Breit-Wigner) approximation with the Beth-Uhlenbeck (BU) approach that takes into account the continuum of quark-antiquark scattering states when determining the partial densities of pions and kaons. We evaluate the kaon-to-pion ratios along the (pseudo-)critical line in the $T - μ_{B}$ plane as a proxy for the chemical freezeout line, whereby the variable $x = T / μ_{B}$ is introduced that corresponds to the conserved entropy per baryon as initial condition for the heavy-ion collision experiments. We present a comparison with the experimental pattern of kaon-to-pion ratios within the BU approach and using $x$ -dependent pion and strange quark potentials. A sharp "horn" effect in the energy dependence $K^{+} / π^{+}$ ratio is explained by the enhanced pion production at energies above $s_{N N} = 8$ GeV, when the system enters the regime of meson dominance. This effect is in line with the enhancement of low-momentum pion spectra that is discussed as a precursor of the pion Bose condensation and entails the occurrence of a nonequilibrium pion chemical potential of the order of the pion mass. We elucidate that the horn effect is not related to the existence of a critical endpoint in the QCD phase diagram.
↳ hep-phhep-exnucl-thEur.Phys.J.ST(2020)·5 citations

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