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Fu-Ming Liu

Publications and source records attributed to Fu-Ming Liu.

At least 19 recordsLinked to original sources
arXiv2026

On the Role of Prompt Photons in the Anisotropic Emission of Direct Photons -- Direct Photons from Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV with IP-Glasma Initial Condition

The anisotropic emission of direct photons from Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV was calculated using a (3+1)-dimensional viscous hydrodynamic model with the impact parameter Glasma initial condition. The transverse momentum spectra of direct photons in different centrality bins (0-20\%, 20-40\%, and 40-60\%) are in good agreement with experimental data measured at RHIC. For the elliptic flow $v_{2}$ and triangular flow $v_{3}$, the agreement is centrality dependent, showing good correspondence for the 20-40\% bin but underprediction for the 0-20\% bin and overprediction for the 40-60\% bin. After carefully accounting for the contribution from prompt photons, the measured $v_{2}$ of direct photons is no longer too large to explain. An overestimation of the prompt photon yield can suppress the $v_2$ and $v_3$ of direct photons to values lower than those observed in the experimental data.

hep-ph↗
arXiv2016

Anisotropic emission of direct photons and thermal dileptons from Au+Au collisions at $\sqrt{s_{NN}}=200$~GeV with EPOS3

Electromagnetic probes such as direct photons and dileptons are crucial to study the properties of a Quark-Gluon Plasma (QGP) created in heavy ion collisions. Based on the (3+1)-dimensional event-by-event viscous hydrodynamic model EPOS 3.102, we calculated the anisotropic emission of thermal photons and dileptons in Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) energy $\sqrt{s_{NN}}=200$~GeV. Thermal emissions from both QGP phase and hadronic gas phase are considered, with AMY rate for photons and Lattice QCD based rates for dileptons in QGP phase. For emission from hadron gas phase, rates based vector meson dominant model are used for both photons and dileptons. Non-thermal contribution to direct photons is calculated with next to leading order QCD. STAR cocktail data are directly used for non-thermal contribution to dileptons. With the same space-time evolution of the collision systems, the two penetrating probes, photons and dileptonsshow some consistency, ie, the emission of both thermal photons and dileptons are underestimated, compared with the transverse momentum spectra of direct photons measured by PHENIX collaboration and the invariant mass spectra of dileptons measured by STAR collaboration, for all centrality classes. With a good constraint of anisotropy of the plasma via the elliptic flow and triangular flow of charged hadrons, the resulted elliptic flow and triangular flow of direct photons agree with PHENIX measurements reasonably well. Thus we made predictions to the flows of thermal dileptons. The elliptic flow of thermal dileptons is predicted larger than the available results from other models, and comparable to the STAR measurement referring to all dileptons (thermal + cocktail) for minimal bias collisions.

hep-ph↗
arXiv2016

Anisotropic emission of thermal dielectrons from Au+Au collisions at $\sqrt{s_{NN}}=200$~GeV with EPOS3

Dileptons, as an electromagnetic probe, are crucial to study the properties of a Quark-Gluon Plasma (QGP) created in heavy ion collisions. We calculated the invariant mass spectra and the anisotropic emission of thermal dielectrons from Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) energy $\sqrt{s_{NN}}=200$~GeV based on EPOS3. This approach provides a realistic (3+1)-dimensional event-by-event viscous hydrodynamic description of the expanding hot and dense matter with a very particular initial condition, and a large set of hadron data and direct photons (besides $v_{2}$ and $v_{3}$ !) can be successfully reproduced. Thermal dilepton emission from both the QGP phase and the hadronic gas are considered, with the emission rates based on Lattice QCD and a vector meson model, respectively. We find that the computed invariant mass spectra (thermal contribution + STAR cocktail) can reproduce the measured ones from STAR at different centralities. Different compared to other model predictions, the obtained elliptic flow of thermal dileptons is larger than the STAR measurement referring to all dileptons. We observe a clear centrality dependence of thermal dilepton not only for elliptic flow $v_{2}$ but also for higher orders. At a given centrality, $v_{n}$ of thermal dileptons decreases monotonically with $n$ for $2\leq n\leq5$.

hep-ph↗
arXiv2015

Anisotropic emission of direct photons from Au+Au collisions at $\sqrt {s_{\rm NN}}=200~{\rm GeV}$ with EPOS3 and IP-Glasma

The observed large elliptic flow ($v_2$) of direct photons in relativistic heavy ion collisions challenges us to explain. In this paper we consider only two sources of direct photons, prompt photons and thermal photons. Prompt photons are calculated with QCD to next leading order, which fits well the spectra at high transverse momentum ($p_{\rm t}$) region. Thermal photons are calculated with AMY rate in a 3+1D viscous hydrodynamical evolution of the collision systems. Two types of initial conditions, EPOS3 and IP-Glasma, are employed. Our results with IP-Glasma initial condition agree with results in published work in most cases, and the difference tells the regions effected by the absence of viscous correction in photon emission rate. Because both models are well constrained with hadron data, the hydrodynamic evolution of collision systems in the two models have many common. However, the transverse velocity of the collective motion are quite different. This makes a big difference in the anisotropic emission of direct photon emission. The observed large elliptic flow of direct photons is reproduced with EPOS3 hydrodynamic evolution.

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arXiv2015

QGP formation time and the large photon v2 puzzle in heavy ion collisions

We investigate the large photon v2 puzzle and the two time scales of thermal and chemical equilibrium in heavy ion collisions. The two-time-scale picture has a weak effect on the transverse moemntum spectrum of direct photons, but a strong effect on the elliptic flow of direct photons. Thus both the spectrum and the elliptic flow of direct photons may be explained with hydro evolution constrained with hadron data. In such a picture, a gluon dominant matter appears in heavy ion collisions. This new matter may impact strongly to other fields such as astrophysics and cosmology.

hep-ph↗
arXiv2014

QGP formation time and direct photons from heavy ion collisions

We investigated the information carried by the data of direct photons, ie, the transverse momentum spectrum and the elliptic flow $v_{2}$ from Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76TeV measured at Large Hadron Collider (LHC) and from Au+Au collisions at $\sqrt{s_{NN}}$= 200 GeV measured at Relativistic Heavy Ion Collider (RHIC), in the frame work of (3+1)-dimensional ideal hydrodynamical models constrained with hadronic data. We found those direct photon data may serve as a useful clock at the early stage of heavy ion collisions. The time scales of reaching thermal and chemical equilibrium, extracted from those data, are about 1/3 and 1.5 fm/c, respectively. Thus the large elliptic flow of direct photons is explainable. High order harmonics, ie, $v_3$, $v_4$ and $v_5$, of direct photons from Pb+Pb collisions at 2.76TeV are also predicted, as a further test to compete with those who claim new sources of photons to account for the large elliptic flow of direct photons.

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arXiv2012

Landau hydrodynamical model at RHIC and LHC

The rapidity distribution and transverse spectra of most copious particles such as pions, Kaons and antiprotons from central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV and central Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV have been investigated in the framework of Landau hydrodynamical model. With a more realistic choice of freeze-out condition and the employment of lattice equation of state, we find transverse expansion of the collision systems is important to explain the observed data. With the increase of collision energy from RHIC to LHC, transverse flow becomes more and more important for hadron production at midrapidity, especially for more massive particle.

hep-ph↗
arXiv2011

On QGP Formation in pp Collisions at 7 TeV

The possibility of QGP formation in central pp collisions at ultra-high collision energy is discussed. Centrality-dependent $\pt$-spectra and (pseudo)rapidity spectra of thermal photons (charged hadrons) from pp collisions at 7 TeV are presented (addressed). Minimal-bias $\pt$-spectrum of direct photons and charged hadrons is compared under the framework with and without hydrodynamical evolution process.

hep-ph↗
arXiv2011

Direct photons at low transverse momentum -- a QGP signal in pp collisions at LHC

We investigate photon production in a scenario of quark-gluon plasma formation in proton-proton scattering at 7 TeV. It is shown that thermal photon yields increase quadratically with the charged particle multiplicity. This gives an enhanced weight to high multiplicity events, and leads to an important photon production even in minimum bias events, where the thermal photons largely dominate over the prompt ones at transverse momentum values smaller than 10 GeV/c.

hep-ph↗
arXiv2011

Mach cone induced by $γ$-triggered jets in high-energy heavy-ion collisions

MMedium excitation by jet shower propagation inside a quark-gluon plasma is studied within a linear Boltzmann transport and a multiphase transport model. Contrary to the naive expectation, it is the deflection of both the jet shower and the Mach-cone-like excitation in an expanding medium that is found to gives rise to a double-peak azimuthal particle distribution with respect to the initial jet direction. Such deflection is the strongest for hadron-triggered jets which are often produced close to the surface of dense medium due to trigger-bias and travel against or tangential to the radial flow. Without such trigger bias, the effect of deflection on $γ$-jet showers and their medium excitation is weaker. Comparative study of hadron and $γ$-triggered particle correlations can therefore reveal the dynamics of jet-induced medium excitation in high-energy heavy-ion collisions.

nucl-th↗
arXiv2010

Dihadron and gamma-hadron correlations from jet-induced medium excitation in high-energy heavy-ion collisions

Jet propagation is shown to produce Mach-cone-like medium excitation inside a quark-gluon plasma. However, only deflection of such medium excitation and jet shower partons by radial flow leads to double-peaked dihadron correlation in high-energy heavy-ion collisions. Dihadron correlations from harmonic flow, hot spots and dijets are studied separately within the AMPT Monte Carlo model and all lead to double-peaked dihadron azimuthal correlation. The $γ$-hadron correlation has similar double-peak feature but is free of the contributions from harmonic flow and hot spots. Dihadron and $γ$-hadron correlations are compared to shed light on jet-induced medium excitation and hot spots in an expanding medium.

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arXiv2010

A Theoretic Review of Centrality-Dependent Direct Photon pt spectra in Au+Au Collisions at 200 GeV

The recently published PHENIX data of direct photons at low pt from Au+Au collisions at the BNL relativestic Heavy Ion Collider (RHIC) energy 200 GeV have attracted a lot of theoretic interest. Here I review our theoretical calculation which successfully reproduces the measured pt spectra of direct photons from Au+Au at different centralities over a wide pt range, in order to show a close relation between hadronic observables and those of direct photons.

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arXiv2009

Elliptic flow of thermal photons at midrapidity in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV

The elliptic flow $v_{2}$ of thermal photons at midrapidity in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV is predicted, based on three-dimensional ideal hydrodynamics. Because of the interplay between the asymmetry and the strength of the transverse flow, the thermal photon $v_{2}$ reaches a maximum at $\pt \sim $ 2GeV/$c$ and the $\pt$-integrated $v_{2}$ reaches a maximum at about 50% centrality. The $\pt$-integrated $v_{2}$ is very sensitive to the lower limit of the integral but not sensitive to the upper limit due to the rapid decrease in the spectrum of the transverse momentum.

hep-ph↗
arXiv2009

Elliptic flow of thermal photons in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV

The transverse momentum (pt) dependence, the centrality dependence and the rapidity dependence of the elliptic flow of thermal photons in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV are predicted, based on a three-dimensional ideal hydrodynamic description of the hot and dense matter. The elliptic flow parameter $v_{2}$, i.e. the second Fourier coefficient of azimuthal distribution, of thermal photons, first increases with $\pt$ and then decreases for $\pt>$ 2 GeV/$c$, due to the weak transverse flow at the early stage. The $\pt$-integrated $v_{2}$ first increases with centrality, reaches a maximum at about 50% centrality, and decreases. The rapidity dependence of the elliptic flow $v_{2}(y)$ of direct photons (mainly thermal photons) is very sensitive to the initial energy density distribution along longitudinal direction, which provides a useful tool to extract the realistic initial condition from measurements.

hep-ph↗
arXiv2008

Jet quenching and direct photon production

Jet quenching effect has been investigated in the direct photon production, based on a realistic data-constrained (3+1) dimensional hydrodynamic description of the expanding hot and dense matter, a reasonable treatment of the propagation of partons and their energy loss in the fluid, and a systematic study of the main sources of direct photons. Our resultant $\pt$ spectra agree with recent PHENIX data in a broad $\pt$ range. Parton energy loss in the plasma eventually effect significantly direct photon production from fragmentation and jet photon conversion, similar to hadron suppression in central heavy ion collisions. But this only causes about 40% decrease in the total production of direct photons, due to the mixture with other direct photon sources.

hep-ph↗
arXiv2008

Centrality-dependent direct photon pt spectra in Au+Au collisions at RHIC

We calculate the centrality-dependence of transverse momentum ($\pt$) spectra for direct photons in Au+Au collisions at the RHIC energy, based on a realistic data-constrained (3+1) dimensional hydrodynamic description of the expanding hot and dense matter, a reasonable treatment of the propagation of partons and their energy loss in the fluid, and a systematic study of the main sources of direct photons. The resultant $\pt$ spectra agree with recent PHENIX data in a broad $\pt$ range. The competition among the different direct photon sources is investigated at various centralities. Parton energy loss in the plasma is considered for photons from fragmentation and jet photon conversion, which causes about 40% decrease in the total contribution. In the high $\pt$ region, the observed $R_{AA}$ of photons is centrality independent at the accuracy of 5% based on a realistic treatment of energy loss. We also link the different behavior of $R_{AA}$ for central and peripheral collisions, in the low $\pt$ region, to the fact that the plasma in central collisions is hotter compared to peripheral ones.

hep-ph↗
arXiv2007

A Systematic Study on Direct Photon Production from Central Heavy Ion Collisions

We investigate the production of direct photons in central Au-Au collisions at the relativistic Heavy-Ion Collider (RHIC) at 200 GeV per nucleon, considering all possible sources. We treat thermal photons emitted from a quark-gluon plasma and from a hadron gas, based on a realistic thermodynamic expansion. Hard photons from elementary nucleon-nucleon scatterings are included: primordial elementary scatterings are certainly dominant at large transverse momenta, but also secondary photons from jet fragmentation and jet-photon conversion cannot be ignored. In both cases we study the effect of energy loss, and we also consider photons emitted from bremsstrahlung gluons via fragmentation.

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