arXiv subjects

Guang-You Qin

Publications and source records attributed to Guang-You Qin.

At least 91 records · Page 5Linked to original sources

arXiv2016

Drag induced radiative energy loss of semi-hard heavy quarks

We revisited gluon bremsstrahlung off a heavy quark in nuclear matter within higher twist formalism. In this work, we demonstrate that, in addition to transverse momentum diffusion parameter ($\hat q$), the gluon emission spectrum for a heavy quark is quite sensitive to $\hat e$, which quantify the amount of light-cone drag experienced by a parton. This effect leads to an additional energy loss term for heavy-quarks. From heavy flavor suppression data in ultra-relativistic heavy-ion collisions one can now estimate the value of this sub-leading non-perturbative jet transport parameter ($\hat e$) from our results.

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arXiv2016

Photon bremsstrahlung from quark jet via transverse and longitudinal scatterings: single versus multiple scatterings

We study the production of jet-bremsstrahlung photons through the scattering with the constituents of a dense nuclear matter within the framework of deep-inelastic scattering off a large nucleus. Applying a gradient expansion up to the second order for the exchanged three-dimensional momentum between jet and medium, we derive the single photon bremsstrahlung spectrum with the inclusion of the contributions from the transverse broadening as well as the longitudinal drag and diffusion of the hard parton's momentum. We also compare the medium-induced photon radiation spectra for single scattering and from the resummation of multiple scatterings. It is found that the coupling between different scatterings can give additional contribution to medium-induced photon radiation, while for small momentum exchange, the leading contribution from the drag and diffusions to the photon emission spectra remain the same for single and multiple scatterings.

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arXiv2016

Full jet evolution in quark-gluon plasma and nuclear modification of jet production and jet shape in Pb+Pb collisions at 2.76 ATeV at the LHC

We study the evolution of full jet shower in quark-gluon plasma via solving a set of coupled differential transport equations for the three-dimensional momentum distributions of quarks and gluons contained in the full jets. In our jet evolution equations, we include all partonic splitting processes as well as the collisional energy loss and transverse momentum broadening for both the leading and radiated partons of the full jets. Combining with a realistic (2+1)-dimensional viscous hydrodynamic simulation for the space-time profiles of the hot and dense nuclear medium produced in heavy-ion collisions, we apply our formalism to calculate the nuclear modification of single inclusive full jet spectra, the momentum imbalance of photon-jet and dijet pairs, and jet shape function (at partonic level) in Pb+Pb collisions at 2.76 ATeV. The roles of various jet-medium interaction mechanisms on the full jet modification are studied. We find that the nuclear modification of jet shape is sensitive to the interplay of different interaction mechanisms as well as the energies of the full jets.

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arXiv2016

Gluon contribution to open heavy-meson production in heavy-ion collisions

A sizable contribution to heavy quark production in high-energy hadronic and nuclear collisions comes from heavy quark-antiquark pair production from gluon splitting during the parton shower evolution. We investigate the effect of gluon-medium interaction on open heavy flavor spectra in ultra-relativistic heavy-ion collisions. The interaction of hard gluons and heavy quarks with the hot QCD medium is simulated by utilizing a Langevin transport model that simultaneously incorporates contributions from collisional and radiative processes. It is found that while the gluon splitting channel has quite an important contribution to the single $D$ meson production cross section, its influence on the final heavy meson nuclear modification turns out to be quite modest because the average lifetime of hard gluons is short before splitting into heavy quark-antiquark pairs during the evolution and propagation of the parton shower.

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arXiv2015

The Influence of Initial State Fluctuations on Heavy Quark Energy Loss in Relativistic Heavy-ion Collisions

We study the effects of initial state fluctuations on the dynamical evolution of heavy quarks inside a quark-gluon plasma created in relativistic heavy-ion collisions. The evolution of heavy quarks in QGP matter is described utilizing a modified Langevin equation that incorporates the contributions from both collisional and radiative energy loss. The spacetime evolution of the fireball medium is simulated with a (2+1)-dimensional viscous hydrodynamic model. We find that when the medium traversed by the heavy quark contains a fixed amount of energy, heavy quarks tend to lose more energy for greater fluctuations of the medium density. This may result in a larger suppression of heavy flavor observables in a fluctuating QGP matter than in a smooth one. The possibility of using hard probes to infer the information of initial states of heavy-ion collisions is discussed.

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arXiv2015

Modeling of heavy-flavor pair correlations in Au-Au collisions at 200 A GeV at the BNL Relativistic Heavy Ion Collider

We study the nuclear modification of angular and momentum correlations between heavy quark pairs in ultrarelativistic heavy-ion collisions. The evolution of heavy quarks inside the thermalized medium is described via a modified Langevin approach that incorporates both elastic and inelastic interactions with the medium constituents. The spacetime evolution of the fireball is obtained from a (2+1)-dimensional viscous hydrodynamics simulation. The hadronization of heavy quarks is performed utilizing a hybrid model of fragmentation and coalescence. Our results show that the nuclear modification of the transverse momentum imbalance of D\bar{D} pairs reflects the total energy loss experienced by the heavy quarks and may help us probe specific regions of the medium. The angular correlation of heavy flavor pairs, especially in the low to intermediate transverse momentum regime, is sensitive to the detailed energy loss mechanism of heavy quarks inside the QGP.

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arXiv2015

Decorrelation of anisotropic flows along the longitudinal direction

The initial energy density distribution and fluctuation in the transverse direction lead to anisotropic flows of final hadrons through collective expansion in high-energy heavy-ion collisions. Fluctuations along the longitudinal direction, on the other hand, can result in decorrelation of anisotropic flows in different regions of pseudo rapidity ($η$). Decorrelation of the $2$nd and $3$rd order anisotropic flows with different $η$ gaps for final charged hadrons in high-energy heavy-ion collisions is studied in an event-by-event (3+1)D ideal hydrodynamic model with fully fluctuating initial conditions from A Multi-Phase Transport (AMPT) model. The decorrelation of anisotropic flows of final hadrons with large $η$ gaps are found to originate from the spatial decorrelation along the longitudinal direction in the AMPT initial conditions through hydrodynamic evolution. The decorrelation is found to consist of both a linear twist and random fluctuation of the event-plane angles. The agreement between our results and recent CMS data in most centralities suggests that the string-like mechanism of initial parton production in AMPT model captures the initial longitudinal fluctuation that is responsible for the measured decorrelation of anisotropic flows in Pb+Pb collisions at LHC. Our predictions for Au+Au collisions at the highest RHIC energy show stronger longitudinal decorrelation, indicating larger longitudinal fluctuations at lower beam energies. Our study also calls into question some of the current experimental methods for measuring anisotropic flows and extraction of transport coefficients through comparisons to hydrodynamic simulations that do not include longitudinal fluctuations.

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arXiv2015

Jet quenching in high-energy heavy-ion collisions

Jet quenching in high-energy heavy-ion collisions can be used to probe properties of hot and dense quark-gluon plasma. We provide a brief introduction to the concept and framework for the study of jet quenching. Different approaches and implementation of multiple scattering and parton energy loss are discussed. Recent progresses in the theoretical and phenomenological studies of jet quenching in heavy-ion collisions at RHIC and LHC are reviewed.

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arXiv2015

Heavy-flavor dynamics in relativistic p-Pb collisions at $\sqrt{S_{NN}}=5.02$ TeV

We investigate the heavy flavor dynamics in the quark-gluon plasma (QGP) medium created in p-Pb collisions at the CERN Large Hadron Collider (LHC). In the (3+1)-dimensional viscous hydrodynamics model describing QGP medium, the dynamics of heavy quarks are studied in an improved Langevin framework incorporating both collisional and radiative energy loss. The hadronization of the heavy quarks is given by a hybrid model of fragmentation and recombination. We find that the in-medium evolution of charm quarks raises the D-meson $R_{pPb}$ at low transverse momenta while it suppresses the D-meson $R_{pPb}$ at intermediate momenta. In addition, the elliptic flow of D-meson is calculated. For a diffusion coefficient which reproduces central $R_{AA}$ data at the LHC, we find a much smaller D-meson $v_2$ compared to the light hadrons. This observation indicates an incomplete coupling between heavy quarks with the medium, due to the reduced medium size compared to AA collisions.

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arXiv2015

Energy loss, hadronization and hadronic interactions of heavy flavors in relativistic heavy-ion collisions

We construct a theoretical framework to describe the evolution of heavy flavors produced in relativistic heavy-ion collisions. The in-medium energy loss of heavy quarks is described using our modified Langevin equation that incorporates both quasi-elastic scatterings and the medium-induced gluon radiation. The space-time profiles of the fireball is described by a (2+1)-dimensional hydrodynamics simulation. A hybrid model of fragmentation and coalescence is utilized for heavy quark hadronization, after which the produced heavy mesons together with the soft hadrons produced from the bulk QGP are fed into the hadron cascade UrQMD model to simulate the subsequent hadronic interactions. We find that the medium-induced gluon radiation contributes significantly to heavy quark energy loss at high $p_\mathrm{T}$; heavy-light quark coalescence enhances heavy meson production at intermediate $p_\mathrm{T}$; and scatterings inside the hadron gas further suppress the $D$ meson $R_\mathrm{AA}$ at large $p_\mathrm{T}$ and enhance its $v_2$. Our calculations provide good descriptions of heavy meson suppression and elliptic flow observed at both the LHC and RHIC.

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arXiv2015

Jet transport and photon bremsstrahlung via longitudinal and transverse scattering

We study the effect of multiple scatterings on the propagation of hard partons and the production of jet-bremsstrahlung photons inside a dense medium in the framework of deep-inelastic scattering off a large nucleus. We include the momentum exchanges in both longitudinal and transverse directions between the hard partons and the constituents of the medium. Keeping up to the second order in a momentum gradient expansion, we derive the spectrum for the photon emission from a hard quark jet when traversing dense nuclear matter. Our calculation demonstrates that the photon bremsstrahlung process is influenced not only by the transverse momentum diffusion of the propagating hard parton, but also by the longitudinal drag and diffusion of the parton momentum. A notable outcome is that the longitudinal drag tends to reduce the amount of stimulated emission from the hard parton.

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arXiv2015

Longitudinal Decorrelation of Anisotropic Flows in Heavy-ion Collisions at the CERN Large Hadron Collider

Fluctuations in the initial transverse energy-density distribution lead to anisotropic flows as observed in central high-energy heavy-ion collisions. Studies of longitudinal fluctuations of the anisotropic flows can shed further light on the initial conditions and dynamical evolution of the hot quark-gluon matter in these collisions. Correlations between anisotropic flows with varying pseudorapidity gaps in Pb+Pb collisions at the CERN Large Hadron Collider are investigated using both an event-by-event (3+1)-D ideal hydrodynamical model with fluctuating initial conditions and the a multiphase transport (AMPT) Monte Carlo model for high-energy heavy-ion collisions. Anisotropic flows at different pseudorapidities are found to become significantly decorrelated with increasing pseudo-rapidity gaps due to longitudinal fluctuations in the initial states of heavy-ion collisions. The longitudinal correlation of the elliptic flow shows a strong centrality dependence while the correlation of the triangular flow is independent of the centrality. Longitudinal fluctuations as a source of the decorrelation are further shown to consist of a twist or gradual rotation in flow angles between the forward and backward direction and additional fluctuations on top of the twist. Within the AMPT model, longitudinal correlations of anisotropic flows are also found to depend on the value of partonic cross sections. The implicatiosn of constraining the initial conditions and shear viscosity to entropy density ratio of the partonic matter in high-energy heavy-ion collisions are also discussed.

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arXiv2015

Anisotropic Flow and Jet Quenching in Relativistic Nuclear Collisions

The exploration of the strong-interaction matter under extreme conditions is one of the main goals of relativistic heavy-ion collisions. We provide some of the main results on the novel properties of quark-gluon plasma, with particular focus given to the strong collectivity and the color opaqueness exhibited by such hot and dense matter produced in high-energy nuclear collisions at RHIC and the LHC.

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arXiv2014

Theory of Jet Quenching in Ultra-Relativistic Nuclear Collisions

We present a short overview of recent progress in the theory of jet quenching in ultra-relativistic nuclear collisions, including phenomenological studies of jet quenching at RHIC and the LHC, development in NLO perburbative QCD calculation of jet broadening and energy loss, full jet evolution and modification, medium response to jet transport, and lattice QCD and AdS/CFT studies of jet quenching.

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arXiv2014

Heavy Flavor Dynamics in QGP and Hadron Gas

We study heavy flavor evolution in the quark-gluon plasma matter and the subsequent hadron gas created in ultrarelativistic heavy-ion collisions. The motion of heavy quarks inside the QGP is described using our modified Langevin framework that incorporates both collisional and radiative energy loss mechanisms; and the scatterings between heavy mesons and the hadron gas are simulated with the UrQMD model. We find that the hadronic interaction further suppresses the $D$ meson $R_\mathrm{AA}$ at high $p_\mathrm{T}$ and enhances its $v_2$. And our calculations provide good descriptions of experimental data from both RHIC and LHC. In addition, we explore the heavy-flavor-tagged angular correlation functions and find them to be a potential candidate for distinguishing different energy loss mechanisms of heavy quarks inside the QGP.

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arXiv2014

Parton shower evolution in medium and nuclear modification of photon-tagged jets in Pb+Pb collisions at the LHC

We study the medium modification of jets correlated with large transverse momentum photons at the LHC via a transport and perturbative QCD hybrid model which incorporates the contributions from both elastic collisions and radiative energy loss experienced by the parton showers. Calculations are performed for the modification of the photon-tagged jet yield, the photon-jet energy imbalance, and the azimuthal distribution of away-side jets. The modifications of photon-tagged jets with different $x_T = p_{T, J}/p_{T, γ}$ values are studied and they exhibit different centrality and jet cone size dependence due to traversing different medium lengths and density profiles. We further investigate the influence of transverse and longitudinal jet transport coefficients on the nuclear modification of photon-tagged jet production and jet shape observables.

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arXiv2014

Dynamical Evolution, Hadronization and Angular De-correlation of Heavy Flavor in a Hot and Dense QCD Medium

We study heavy flavor evolution and hadronization in relativistic heavy-ion collisions. The in-medium evolution of heavy quarks is described using our modified Langevin framework that incorporates both collisional and radiative energy loss mechanisms. The subsequent hadronization process for heavy quarks is calculated with a fragmentation plus recombination model. We find significant contribution from gluon radiation to heavy quark energy loss at high $p_T$; the recombination mechanism can greatly enhance D meson production at medium $p_T$. Our calculation provides a good description of D meson nuclear modification at the LHC. In addition, we explore the angular correlation functions of heavy flavor pairs which may provide us a potential candidate for distinguishing different energy loss mechanisms of heavy quarks inside QGP.

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arXiv2014

Elliptic and triangular flow anisotropy in deuteron-gold collisions at RHIC and proton-lead collisions at the LHC

We study elliptic and triangular flow in the collisions of deuteron-gold nuclei at $\sqrt{s_{\rm NN}} = 200$ GeV at RHIC and of proton-lead nuclei at $\sqrt{s_{\rm NN}} = 5.02$ TeV at the LHC, utilizing (3+1)-dimensional ideal hydrodynamics for the dynamic evolution of the fireball and a Glauber-based Monte-Carlo energy deposition model for simulating the fluctuating initial conditions. Sizable values of elliptic and triangular flow are obtained for both colliding systems, and the results are consistent with PHENIX, ALICE, ATLAS and CMS measurements. For these studied centralities, we find that the elliptic flow in proton-lead collisions is smaller than deuteron-gold collisions, while the triangular flows are comparable in both colliding systems. Our results indicate that the observed collective anisotropic flow in deuteron-gold and proton-lead collisions may be obtained from relativistic hydrodynamic evolution of the fireball with initial state fluctuations.

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