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Xin-Nian Wang

Publications and source records attributed to Xin-Nian Wang.

At least 91 records · Page 5Linked to original sources
arXiv2020

Study of heavy-flavor jets in a transport approach

Measurements at the RHIC and the LHC have observed flavor dependence of single-hadron suppression, which reveal the role played by quark masses in the parton interactions with the quark-gluon plasma (QGP) medium. In this study, we explore the manifestation of quark mass effect and flavor dependence in jet observables. We approach this study using the LIDO transport model. Both elastic and medium-induced radiative processes are implemented for hard parton evolution in the medium. To guarantee energy-momentum conservation in the model for the study of full jet observables, we also include a component that mimics the energy-momentum transported by medium excitation. We first predict the heavy-jet (B-jet, D-jet) and inclusive-jet nuclear modification factor $R_{AA}$ in central nuclear collisions at both the RHIC and the LHC beam energies. We observe a flavor-dependent jet suppression as a function of jet transverse momentum, which can be tested by future precision measurements of heavy jets. We further investigate a novel observable that considers the angular correlation between two hard objects: a D-meson and a jet, which provides model constraints in addition to those imposed by inclusive measurements.

nucl-th↗
arXiv2020

Report from the A.I. For Nuclear Physics Workshop

This report is an outcome of the workshop "AI for Nuclear Physics" held at Thomas Jefferson National Accelerator Facility on March 4-6, 2020. The workshop brought together 184 scientists to explore opportunities for Nuclear Physics in the area of Artificial Intelligence. The workshop consisted of plenary talks, as well as six working groups. The report includes the workshop deliberations and additional contributions to describe prospects for using AI across Nuclear Physics research.

physics.comp-ph↗
arXiv2020

Identifying the nature of the QCD transition in relativistic collision of heavy nuclei with deep learning

Using deep convolutional neural network (CNN), the nature of the QCD transition can be identified from the final-state pion spectra from hybrid model simulations of heavy-ion collisions that combines a viscous hydrodynamic model with a hadronic cascade "after-burner". Two different types of equations of state (EoS) of the medium are used in the hydrodynamic evolution. The resulting spectra in transverse momentum and azimuthal angle are used as the input data to train the neural network to distinguish different EoS. Different scenarios for the input data are studied and compared in a systematic way. A clear hierarchy is observed in the prediction accuracy when using the event-by-event, cascade-coarse-grained and event-fine-averaged spectra as input for the network, which are about 80%, 90% and 99%, respectively. A comparison with the prediction performance by deep neural network (DNN) with only the normalized pion transverse momentum spectra is also made. High-level features of pion spectra captured by a carefully-trained neural network were found to be able to distinguish the nature of the QCD transition even in a simulation scenario which is close to the experiments.

hep-ph↗
arXiv2020

Medium modification of $γ$-jet fragmentation functions in Pb+Pb collisions at LHC

Coupled linear Boltzmann transport and hydrodynamic (CoLBT-hydro) model has been developed for simultaneous simulations of jet propagation and jet-induced medium excitation in heavy-ion collisions. Within this coupled approach, the final reconstructed jets in heavy-ion collisions include not only hadrons from the hadronization of medium modified jet shower partons from the linear Boltzmann transport (LBT) but also hadrons from the freeze-out of the jet-induced medium excitation in the hydrodynamic evolution of the bulk medium. Using the CoLBT-hydro model, we study medium modification of the fragmentation functions of $γ$-triggered jets in high-energy heavy-ion collisions at the Large Hadron Collider. The CoLBT-hydro model is shown to describe the experimental data not only on the suppression of leading hadrons within the jet cone at large momentum fraction $z_γ=p_T^h/p_T^γ$ relative to the transverse momentum of the trigger photon due to parton energy loss but also the enhancement of soft hadrons at small $z_γ$ and $z_{\rm jet}=p_T^h/p_T^{\rm jet}$ due to jet-induced medium excitation. There is no suppression of the fragmentation function, however, at large momentum fraction $z_{\rm jet}$ relative to the transverse momentum of the reconstructed jet due to trigger bias and medium modification of quark to gluon jet fraction. For jets whose final transverse momenta are comparable to or larger than that of the trigger photon, the trigger bias can lead to enhancement of the jet fragmentation function at large $z_{\rm jet}$.

hep-ph↗
arXiv2020

Longitudinal dependence of B and D meson nuclear modifications in heavy-ion collisions at RHIC and the LHC

It is widely acknowledged that heavy flavor probes are sensitive to the properties of the quark-gluon plasma and are often considered an important tool for the plasma tomography studies. Forward rapidity observables can provide further insight on the dynamics of the medium due to the interplay between the medium size and the differences in the production spectra of heavy quark probes. In this proceedings we present the nuclear modification factor $R_\text{AA}$'s for B and D mesons, as well as heavy flavor leptons, in the rapidity range $-4.0 < y < 4.0$ obtained from relativistic Langevin equation with gluon radiation coupled with a (3+1)-dimensional viscous hydrodynamics medium background. We present comparison with experimental data at mid-rapidity as well as predictions for different rapidity ranges.

nucl-th↗
arXiv2020

Jet quenching and medium response in high-energy heavy-ion collisions: a review

Jet quenching has been used successfully as a hard probe to study properties of the quark-gluon plasma (QGP) in high-energy heavy-collisions at both the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC). We will review recent progresses in theoretical and phenomenological studies of jet quenching with jet transport models. Special emphasis is given to effects of jet-induced medium response on a wide variety of experimental measurements and their implication on extracting transport properties of the QGP in heavy-ion collisions.

hep-ph↗
arXiv2019

Global Polarization Effect in the Extremely Rapidly Rotating QGP in HIC

This is prepared for a featured article in Nuclear Physics News. Recently, the global polarization of Λand \barΛ hyperons in heavy-ion collisions (HIC) has been observed by the STAR Collaboration at the Relativistic Heavy Ion Collider in Brookhaven National Laboratory. The discovery confirms the theoretical prediction made more than ten years ago and indicates that the quark gluon plasma (QGP) produced in HIC possesses a vorticity as high as 10^21s^-1, much higher than any other fluid observed in nature. This opens a new window to study properties of QGP and a new direction in high energy heavy ion physics. This featured article is aimed to report the basic idea, current status and outlook.

nucl-th↗
arXiv2019

Longitudinal dependence of open heavy flavor $R_\text{AA}$ in relativistic heavy-ion collisions

Heavy flavor probes are sensitive to the properties of the quark gluon plasma (QGP) produced in relativistic heavy-ion collisions. A huge amount of effort has been devoted to studying different aspects of the heavy-ion collisions using heavy flavor particles. In this work, we study the dynamics of heavy quark transport in the QGP medium using the rapidity dependence of heavy flavor observables. We calculate the nuclear modification of $\text{B}$ and $\text{D}$ meson spectra as well as spectra of leptons from heavy flavor decays in the rapidity range $[-4.0,4.0]$. We use an implementation of the improved Langevin equation with gluon radiation on top of a (3+1)-dimensional relativistic viscous hydrodynamical background for several collision setups. We find that the rapidity dependence of the heavy quark modification is determined by the interplay between the smaller size of the medium, which affects the path length of the heavy quarks, and the softer heavy quark initial production spectrum. We compare our results with available experimental data and present predictions for open heavy flavor meson $R_\text{AA}$ at finite rapidity.

nucl-th↗
arXiv2019

Parton Energy Loss and the Generalized Jet Transport Coefficient

We revisit radiative parton energy loss in deeply inelastic scattering (DIS) off a large nucleus within the perturbative QCD approach. We calculate the gluon radiation spectra induced by double parton scattering in DIS without collinear expansion in the transverse momentum of initial gluons as in the original high-twist approach. The final radiative gluon spectrum can be expressed in terms of the convolution of hard partonic parts and unintegrated or transverse momentum dependent (TMD) quark-gluon correlations. The TMD quark-gluon correlation can be factorized approximately as a product of initial quark distribution and TMD gluon distribution which can be used to define the generalized or TMD jet transport coefficient. Under the static scattering center and soft radiative gluon approximation, we recover the result by Gylassy-Levai-Vitev (GLV) in the first order of the opacity expansion. The difference as a result of the soft radiative gluon approximation is investigated numerically under the static scattering center approximation.

hep-ph↗
arXiv2019

30 years of jet quenching

In the last 30 years, the physics of jet quenching has gone from an early stage of a pure theoretical idea to initial theoretical calculations, experimental verification and now a powerful diagnostic tool for studying properties of the quark-gluon plasma (QGP) in high-energy heavy-ion collisions. I will describe my collaboration with Miklos Gyulassy in this exciting area of high-energy nuclear physics in the past 30 years on this special occasion of his 70th birthday and discuss what is ahead of us in jet tomographic study of QGP in heavy-ion collisions.

hep-ph↗
arXiv2019

Bayesian extraction of jet energy loss distributions in heavy-ion collisions

Based on the factorization in perturbative QCD, a jet cross sections in heavy-ion collisions can be expressed as a convolution of the jet cross section in $p+p$ collisions and a jet energy loss distribution. Using this simple expression and the Markov Chain Monte Carlo method, we carry out Bayesian analyses of experimental data on jet spectra to extract energy loss distributions for both single inclusive and $γ$-triggered jets in $Pb+Pb$ collisions with different centralities at two colliding energies at the Large Hadron Collider. The average jet energy loss has a dependence on the initial jet energy that is slightly stronger than a logarithmic form and decreases from central to peripheral collisions. The extracted jet energy loss distributions with a scaling behavior in $x=Δp_T /\langle Δp_T\rangle$ have a large width. These are consistent with the linear Boltzmann transport model simulations, in which the observed jet quenching is caused on the average by only a few out-of-cone scatterings.

hep-ph↗
arXiv2019

Interpretable deep learning for nuclear deformation in heavy ion collisions

The structure of heavy nuclei is difficult to disentangle in high-energy heavy-ion collisions. The deep convolution neural network (DCNN) might be helpful in mapping the complex final states of heavy-ion collisions to the nuclear structure in the initial state. Using DCNN for supervised regression, we successfully extracted the magnitude of the nuclear deformation from event-by-event correlation between the momentum anisotropy or elliptic flow ($v_2$) and total number of charged hadrons ($dN_{\rm ch}/dη$) within a Monte Carlo model. Furthermore, a degeneracy is found in the correlation between collisions of prolate-prolate and oblate-oblate nuclei. Using the Regression Attention Mask algorithm which is designed to interpret what has been learned by DCNN, we discovered that the correlation in total-overlapped collisions is sensitive to only large nuclear deformation, while the correlation in semi-overlapped collisions is discriminative for all magnitudes of nuclear deformation. The method developed in this study can pave a way for exploration of other aspects of nuclear structure in heavy-ion collisions.

nucl-th↗
arXiv2019

Towards the determination of heavy-quark transport coefficients in quark-gluon plasma

Several transport models have been employed in recent years to analyze heavy-flavor meson spectra in high-energy heavy-ion collisions. Heavy-quark transport coefficients extracted from these models with their default parameters vary, however, by up to a factor of 5 at high momenta. To investigate the origin of this large theoretical uncertainty, a systematic comparison of heavy-quark transport coefficients is carried out between various transport models. Within a common scheme devised for the nuclear modification factor of charm quarks in a brick medium of a quark-gluon plasma, the systematic uncertainty of the extracted drag coefficient among these models is shown to be reduced to a factor of 2, which can be viewed as the smallest intrinsic systematical error band achievable at present time. This indicates the importance of a realistic hydrodynamic evolution constrained by bulk hadron spectra and of heavy-quark hadronization for understanding the final heavy-flavor hadron spectra and extracting heavy-quark drag coefficient. The transverse transport coefficient is less constrained due to the influence of the underlying mechanism for heavy-quark medium interaction. Additional constraints on transport models such as energy loss fluctuation and transverse-momentum broadening can further reduce theoretical uncertainties in the extracted transport coefficients.

nucl-th↗
arXiv2019

Interplaying mechanisms behind single inclusive jet suppression in heavy-ion collisions

The suppression factor for single inclusive jets in Pb+Pb collisions at the Large Hadron Collider (LHC) has a weak dependence on the transverse momentum $p_T$ and remains almost the same at two colliding energies, $\sqrt{s}=2.76$ and 5.02 TeV, though the central rapidity density of bulk hadrons increases by about 20\%. This phenomenon is investigated within the Linear Boltzmann Transport (LBT) model, which includes elastic and inelastic processes based on perturbative QCD for both jet shower and recoil medium partons as they propagate through a quark-gluon plasma (QGP). With the dynamic evolution of the QGP given by the 3+1D CLVisc hydrodynamic model with event-by-event fully fluctuating initial conditions, single inclusive jet suppression in Pb+Pb collisions from LBT agrees well with experimental data. The weak $\sqrt{s}$ and $p_T$-dependence of the jet suppression factor at LHC are found to result directly from the $\sqrt{s}$-dependence of the initial jet $p_T$ spectra and slow $p_T$-dependence of the jet energy loss. Contributions from jet-induced medium response, influence of radial expansion, both of which depend on jet-cone size, and jet flavor composition all conjoin to give a slow $p_T$-dependence of jet energy loss and the single jet suppression factor $R_{\rm AA}$, their dependence on $\sqrt{s}$ and jet-cone size. Single inclusive jet suppression at $\sqrt{s}=200$ GeV is also predicted that actually decreases slightly with $p_T$ in the $p_T<50$ GeV/$c$ range because of the steeper initial jet spectra though the $p_T$-dependence of the jet energy loss is weaker than that at LHC.

nucl-th↗
arXiv2019

A microscopic description for polarization in particle scatterings

We propose a microscopic description for the polarization from the first principle through the spin-orbit coupling in particle collisions. The model is different from previous ones based on local equilibrium assumptions for the spin degree of freedom. It is based on scatterings of particles as wave packets, an effective method to deal with particle scatterings at specified impact parameters. The polarization is then the consequence of particle collisions in a non-equilibrium state of spins. The spin-vorticity coupling naturally emerges from the spin-orbit one encoded in polarized scattering amplitudes of collisional integrals when one assumes local equilibrium in momentum but not in spin.

nucl-th↗
arXiv2019

Introducing HIJING++: the Heavy Ion Monte Carlo Generator for the High-Luminosity LHC Era

Beyond 2025 we will enter the High-Luminosity era of the LHC, right after the upgrades of the third Long Shutdown of the Large Hadron Collider (LHC). The ongoing state-of-the-art experimental instrument upgrades require high-performance simulation support in the background, that is modern, robust, and comes with long term support. The original FORTRAN based HIJING (Heavy Ion Jet INteraction Generator) has been used intensively since almost three decades by the high energy physics and heavy-ion community. However, it is getting overly challenging to conform to these new requirements. Our novel Monte Carlo event generator, the HIJING++ is the successor of the old FORTRAN version containing all the physics that its predecessor have. Moreover, among others a flexible module handling layer and an analysis interface is also introduced. This latter supports the most popular event container formats such as simple ascii, ROOT and the HepMC format, together with RIVET support. In this paper we compare the pre-release results of HIJING++ with proton-proton experimental data and Pythia8 calculations.

physics.comp-ph↗