arXiv subjects

Yu-Liang Yan

Publications and source records attributed to Yu-Liang Yan.

50 records · Page 3Linked to original sources

arXiv2011

A Hydrodynamic and Transport Model for Ultrarelativistic Heavy Ion Collisions at RHIC and LHC Energies

Combining the hydrodynamic model (Hydro code) and the transport model (PACIAE model), we present the Hydro-PACIAE hybrid model. We use the Hydro-PACIAE hybrid model to calculate Au+Au collisions at $\sqrt{s_{NN}}$=130 GeV and Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV. The obtained pseudo-rapidity and transverse momentum distributions well reproduce the experimental data. This shows that the Hydro-PACIAE hybrid model is useful to describe the ultrarelativistic Heavy Ion Collisions at RHIC and LHC Energies. We used the hybrid model to calculate the elliptical flow for the Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV. The $v_2$ values are bigger than the experimental data at high $p_T$, and will become bigger when the Hydro evolution time is longer. The results indicate that the selection of the transition hypersurface has significant effect on the observable quantities.

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arXiv2011

Longitudinal Fluctuations in Partonic and Hadronic Initial State

Collective flow in collisions between Lead nuclei at LHC are influenced by random initial state fluctuations, especially for odd harmonics. Here we extend fluctuation studies to longitudinal fluctuations, which may have significant effect on the rapidity distribution of odd harmonics. Furthermore center of mass rapidity fluctuations are measurable, but not yet analysed. Here in the PACIAE parton and hadron molecular dynamics model we make an analysis of initial state fluctuations. As previous analyses discussed mainly the effects of fluctuations on eccentricity and the elliptic flow we pay particular attention to the fluctuations of the Center of Mass rapidity of the system, which is conservatively estimated in our model as Δy_{CM} = 0.1, by neglecting all pre-equilibrium emission effects that are increasing the y_{CM} fluctuations.

hep-ph↗

arXiv2011

Light anti-nuclei production in pp collisions at $\sqrt{s}$=7 and 14 TeV

A dynamically constrained coalescence model based on the phase space quantization and classical limit method was proposed to investigate the production of light nuclei (anti-nuclei) in non-single diffractive (NSD) pp collisions at $\sqrt{s}$=7 and 14 TeV. This calculation was based on the final hadronic state in the PYTHIA and PACIAE model simulations, the event sample consisted of 1.2$\times 10^8$ events in both simulations. The PACIAE model calculated $\bar D$ yield of 6.247$\times 10^{-5}$ in NSD pp collisions at $\sqrt{s}$=7 TeV is well comparing with the ALICE rough datum of 5.456$\times 10^{-5}$. It indicated the reliability of proposed method in some extent. The yield, transverse momentum distribution, and rapidity distribution of the $\bar D$, $^3{\bar{He}}$, and $_{\barΛ} ^3{\bar H}$ in NSD pp collisions at $\sqrt{s} $=7 and 14 TeV were predicted by PACIAE and PYTHIA model simulations. The yield resulted from PACIAE model simulations is larger than the one from PYTHIA model. This might reflect the role played by the parton and hadron rescatterings.

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arXiv2011

PACIAE 2.0: An updated parton and hadron cascade model (program) for the relativistic nuclear collisions

We have updated the parton and hadron cascade model PACIAE for the relativistic nuclear collisions, from based on JETSET 6.4 and PYTHIA 5.7 to based on PYTHIA 6.4, and renamed as PACIAE 2.0. The main physics concerning the stages of the parton initiation, parton rescattering, hadronization, and hadron rescattering were discussed. The structures of the programs were briefly explained. In addition, some calculated examples were compared with the experimental data. It turns out that this model (program) works well.

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arXiv2010

Charged particle elliptic flow in p+p collisions at LHC energies in a transport model PACIAE

The parton and hadron cascade model PACIAE based on PYTHIA was used to investigate the charged particle elliptic flow in minimum bias pp collisions at the LHC energies. The strings were distributed randomly in the transverse ellipsoid of the pp collision system with major axis of $R$ (proton radius) and minor axis of $R(1-ξ)$ before parton rescattering. The charged particle elliptic flow as a function of the random number $ξ$ and transverse momentum $p_T$ were investigated. The calculated $v_2/ε$ as a function of reaction energy increases monotonously with increasing reaction energy up to $\sqrt{s}\sim$7 TeV and then turns to saturation. With the parton-parton cross section enlarges three times in parton rescattering, the rapidity integrated charged particle elliptic flow may reach 0.025 at $p_T \sim$2 GeV/c in the minimum bias pp collisions at $\sqrt{s}$=7 TeV.

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arXiv2010

Centrality dependence of forward-backward multiplicity correlation in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV

We have studied the centrality dependence of charged particle forward-backward multiplicity correlation strength in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV with a parton and hadron cascade model, PACIAE, based on PYTHIA. The calculated results are compared with the STAR data. The experimentally observed correlation strength characters: (1) the approximately flat pseudorapidity dependence in central collisions and (2) the monotonous decrease with decreasing centrality are well reproduced. However the theoretical results are bigger than the STAR data for the peripheral collisions. A discussion is given for the comparison among the different models and STAR data.

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arXiv2009

Correlation between event multiplicity and elliptic flow parameter

The elliptic flow parameter (component), $v_2$, in the Fourier expansion of event-by-event charged particle multiplicity azimuthal distribution in the momentum space is studied by taking into account the multiplicity fluctuations. The correlations between charge multiplicity and impact parameter as well as between elliptic flow parameter and impact parameter (multiplicity) are investigated by both the parton and hadron cascade model PACIAE and a multiple phase transport model AMPT. A discussion is given for the event-wise average and particle-wise average in the definition of elliptic flow parameter.

hep-ph↗

arXiv2009

Parton rescattering effect on particle production in ultra-relativistic p+p collisions

The parton rescattering effect on the charged particle production in ultra-relativistic p+p collisions is studied by the parton and hadron cascade model, PACIAE, based on PYTHIA. We have calculated charged particle pseudorapidity density ($dN_{ch}/dη$) at mid-rapidity and the pseudorapidity distribution in inelastic and non-single diffractive p+p collisions at $\sqrt s$=200, 900, 5500, and 14000 GeV with the PYTHIA and PACIAE models. The calculated results of $\sqrt s$=900 GeV are well compared with the ALICE data. The calculated $dN_{ch}/dη$ as a function of center-of-mass energy well meets with the experimental data as well. Comparing the PYTHIA results (without parton rescattering) with the PACIAE results (with parton rescattering), it turned out that the parton rescattering effect plays an important role and this effect increases with increasing center-of-mass energy.

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arXiv2009

Parton rescattering effect on the charged hadron forward-backward multiplicity correlation in $pp$ collisions at $\sqrt s$=200 GeV

The parton rescattering effect on the charged hadron forward-backward multiplicity correlation in $pp$ collisions at $\sqrt s$=200 GeV is studied by a parton and hadron cascade model, PACIAE, based on the PYTHIA model. The calculated multiplicity and pseudorapidity distribution of the final state charged hadron are well compared with experimental data. It turned out that the final state charged hadron pseudorapidity distribution are different from the initial state charged partons. The parton rescattering effect on the charged hadron forward-backward multiplicity correlation increases with increasing parton rescattering strength in the center pseudorapidity region ($|η| <1$). However, this effect becomes weaker in the outer pseudorapidity region ($|η|> 1$).

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arXiv2009

Reexamination for the calculation of elliptic flow and other fourier harmonics

We have argued that the azimuthal symmetry and asymmetry components in fourier expansion of particle momentum azimuthal distribution, $v_n$ (n=0, 1, 2, ...), should be calculated as an average of $cos(nϕ)$ first over particles in an event and then over events (event-wise average) rather than "an average over all particles in all events" (particle-wise average). In case of large centrality (multiplicity) bin the particle-wise average is not accurate because the influence (fluctuation) of particle multiplicity was not taken into account.

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arXiv2009

Centrality bin size dependence of multiplicity correlation in central Au+Au collisions at $\sqrt{s_NN}$=200 GeV}

We have studied the centrality bin size dependence of charged particle forward-backward multiplicity correlation strength in 5%, 0-5%, and 0-10% most central Au+Au collisions at $\sqrt{s_NN}}$=200 GeV with a parton and hadron cascade model, PACIAE based on PYTHIA. The real (total), statistical, and NBD (Negative Binomial Distribution) correlation strengths are calculated by the real events, the mixed events, and fitting the charged particle multiplicity distribution to the NBD, respectively. It is turned out that the correlation strength increases with increasing centrality bin size monotonously. If the discrepancy between real (total) and statistical correlation strengths is identified as dynamical one, the dynamical correlation may just be a few percent of the total (real) correlation.

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arXiv2009

Exploring behaviors of partonic matter forming in early stage of $pp$ and nucleus-nucleus collisions at ultra-relativistic energies

The parton yield, (pseudo)rapidity distribution, and transverse momentum distribution in partonic matter assumed forming in the early stage of $pp$ and nucleus-nucleus collisions at RHIC energy ($\sqrt{s_{NN}}$=200 GeV) and LHC energy ($\sqrt{s_{NN}}$=5.5 TeV for nucleus-nucleus, 5.5 and/or 14 TeV for $pp$) are comparatively investigated with parton and hadron cascade model PACIAE. It turned out that the different parton and anti-parton spectra approach to be similar with reaction energy increasing from RHIC to LHC. We have argued that if the partonic matter forming in Au+Au collisions at RHIC energy is strongly interacting quark-gluon plasma, the one forming in Pb+Pb collisions at LHC energy might approach the real (free) quark-gluon plasma.

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arXiv2008

PACIAE Model Predictions for Pb+Pb Collisions at LHC Compared to the Au+Au Collisions at RHIC

The parton and hadron cascade model PACIAE is used to simulate the 0-6, 15-25, and 35-45 % most central Au+Au collisions at \sqrt{s_{NN}}=19.6, 62.4, 130, and 200 GeV and the 0-10 % most central Pb+Pb collisions at \sqrt{s_{NN}}=5500 GeV. The calculated charged multiplicity and the charged particle transverse momentum distribution, pseudorapidity distribution, and extended longitudinal scaling for Au+Au collisions well agree with the corresponding PHOBOS data. Thus the above observables calculated for Pb+Pb collisions would be a reliable prediction.

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arXiv2008

Theoretical analysis for the apparent discrepancy between pbarp and pp data in charged particle forward-backward multiplicity correlations

The strength of charged particle forward-backward multiplicity correlation in pbar+p and p+p collisions at s^1/2 = 200 GeV is studied by PYTHIA 6.4 and compared to the UA5 and STAR data correspondingly. It is turned out that a factor of 3-4 apparent discrepancy between UA5 and STAR data can be attributed to the differences in detector acceptances and observing bin interval in both experiments. A mixed event method is introduced and used to calculate the statistical correlation strength and the dynamical correlation strengths stemming from the charge conservation, four- momentum conservation, and decay, respectively. It seems that the statistical correlation is much larger than dynamical one and the charge conservation, four-momentum conservation and decay may account for most part of the dynamical correlation. In addition, we have also calculated the correlation strength by fitting the charged particle multiplicity distribution from PYTHIA to the Negative Binomial Distribution and found that the result agrees well with the correlation strength calculated by mixed events.

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