arXiv subjects

Jun Song

Publications and source records attributed to Jun Song.

151 records · Page 9Linked to original sources

arXiv2010

The entropy puzzle and the quark combination model

We use two available methods, the Duhem-Gibbs relation and the entropy formula in terms of particle phase space distributions, to calculate the entropy in a quark combination model. The entropy of the system extracted from the Duhem-Gibbs relation is found to increase in hadronization if the average temperature of the hadronic phase is lower than that of the quark phase. The increase of the entropy can also be confirmed from the entropy formula if the volume of the hadronic phase is larger than 2.5-3.0 times that of the quark phase. So whether the entropy increases or decreases during combination depends on the temperature before and after combination and on how much expansion the system undergoes during combination. The current study provides an example to shed light on the entropy issue in the quark combination model.

nucl-th↗

arXiv2010

Hadron yield correlation and constituent quark degree of freedom in heavy ion collisions

Based on the assumption of the production of deconfined quark matter, we use a quark combination model to systematically investigate hadron yields in heavy ion collisions from RHIC $\sqrt{s_{NN}}=200, 130, 62.4$ GeV to SPS $E_{beam}=158, 80, 40, 30, 20 $ AGeV. We find that as the collision energy is greater than or equal to 30 AGeV the yields of various hadrons, their correlations, in particular, the observables $A=\frac{\barΛ k^{-} p}{Λk^{+} \bar{p}}$ and $B=\frac{Λk^{-}\barΞ^{+}}{\barΛ k^{+}Ξ^{-}}$, are all reproduced; however, as the collision energy drops to 20 AGeV quark combination fails. This indicates that the constituent quark degrees of freedom represent a decisive factor in thermal hadron production above 30 AGeV and seem to be invalid at 20 AGeV. In addition, hadron yields as well as particle ratios at midrapidity in the most central Pb+Pb collisions at $\sqrt{s_{NN}}=5.5$ TeV are predicted.

hep-ph↗

arXiv2009

Hadron production by quark combination in central Pb+Pb collisions at $\sqrt{s_{NN}}= 17.3$ GeV

The quark combination mechanism of QGP hadronization is applied to nucleus-nucleus collisions at top SPS energy. The yields, rapidity and transverse momentum distributions of identified hadrons in most central Pb+Pb collisions at $\sqrt{s_{NN}}= 17.3$ GeV are systematically studied. The calculated results are in agreement with the experimental data from NA49 Collaboration. The longitudinal and transverse collective flows and strangeness of the hot and dense quark matter produced in nucleus-nucleus collisions at top SPS energy are investigated. It is found that the collective flow of strange quarks is stronger than light quarks, which is compatible with that at RHIC energies, and the strangeness is almost the same as those at $\sqrt{s_{NN}}=$ 62.4, 130, 200 GeV.

hep-ph↗

arXiv2009

Centrality dependence of $p_{T}$ spectra for identified hadrons in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}= 200$ GeV

The centrality dependence of transverse momentum spectra for identified hadrons at midrapidity in Au+Au collisions at $\sqrt{s_{NN}}= 200$ GeV is systematically studied in a quark combination model. The $\mathrm{{p}_{T}}$ spectra of $π^{\pm}$, $K^{\pm}$, $p(\bar{p})$ and $Λ(\barΛ)$ in different centrality bins and the nuclear modification factors ($R_{CP}$) for these hadrons are calculated. The centrality dependence of the average collective transverse velocity $<β(r)>$ for the hot and dense quark matter is obtained in Au+Au collisions, and it is applied to a relative smaller Cu+Cu collision system. The centrality dependence of $\mathrm{{p}_{T}}$ spectra and the $R_{CP}$ for $π^{0}$, $K_{s}^{0}$ and $Λ$ in Cu+Cu collisions at $\sqrt{s_{NN}}= 200$ GeV are well described. The results show that $<β(r)>$ is only a function of the number of participants $N_{part}$ and it is independent of the collision system.

hep-ph↗

arXiv2009

Centrality, system size and energy dependences of charged-particle pseudo-rapidity distribution

Utilizing the three-fireball picture within the quark combination model, we study systematically the charged particle pseudorapidity distributions in both Au+Au and Cu+Cu collision systems as a function of collision centrality and energy, $\sqrt{s_{NN}}=$ 19.6, 62.4, 130 and 200 GeV, in full pseudorapidity range. We find that: (i)the contribution from leading particles to $dN_{ch}/dη$ distributions increases with the decrease of the collision centrality and energy respectively; (ii)the number of the leading particles is almost independent of the collision energy, but it does depend on the nucleon participants $N_{part}$; (iii)if Cu+Cu and Au+Au collisions at the same collision energy are selected to have the same $N_{part}$, the resulting of charged particle $dN/dη$ distributions are nearly identical, both in the mid-rapidity particle density and the width of the distribution. This is true for both 62.4 GeV and 200 GeV data. (iv)the limiting fragmentation phenomenon is reproduced. (iiv) we predict the total multiplicity and pseudorapidity distribution for the charged particles in Pb+Pb collisions at $\sqrt{s_{NN}}= 5.5$ TeV. Finally, we give a qualitative analysis of the $N_{ch}/ $ and $dN_{ch}/dη/ |_{η\approx0}$ as function of $\sqrt{s_{NN}}$ and $N_{part}$ from RHIC to LHC.

hep-ph↗

arXiv2008

Rapidity dependence of hadron production in central Au+Au collisions at $\sqrt{s_{NN}}= 200$ GeV

The rapidity and transverse momentum spectra for identified hadrons in central Au+Au collisions at $\sqrt{s_{NN}}= 200$ GeV are computed in a quark combination model. The data of rapidity distributions for $π^{\pm}$, $K^{\pm}$, $p(\bar{p})$ and net protons $(p-\bar{p})$ are well described. We also predict rapidity distributions for $K^{0}_{s}$, $Λ(\barΛ)$, $\mathrm{Ξ^{-}}$ ($\mathrm{\barΞ^{_+}}$) and $\mathrm{Ω^{-}}+\mathrm{\barΩ}^{_+}$. The multiplicity ratios of charged antihadrons to hadrons as a function of rapidity are reproduced. The results for ${p}_{T}$ spectra of $π^{\pm}$, $K^{\pm}$, $p(\bar{p})$ and for the $p/π$ ratios in a broader ${p}_{T}$ range agree well with the data. Finally the rapidity dependence of transverse momentum distributions for hadrons are given.

nucl-th↗

arXiv2008

The influence of net-quarks on the yields and rapidity spectra of identified hadrons

Within a quark combination model, we study systematically the yields and rapidity spectra of various hadrons in central Au+Au collisions at $\sqrt{s_{NN}}= 200$ GeV. We find that considering the difference in rapidity between net-quarks and newborn quarks, the data of multiplicities, rapidity distributions for $π^{\pm}$, $K^{\pm}$, $p(\bar{p})$ and, in particular the ratios of charged antihadron to hadron as a function of rapidity, can be well described. The effect of net-quarks on various hadrons is analysed, and the rapidity distributions for $K^{0}_{s}$, $Λ(\barΛ)$, $Σ^{+}(\barΣ^{_-})$, $\mathrm{Ξ^{-}}$ ($\mathrm{\barΞ^{_+}}$) and $\mathrm{Ω^{-}}(\mathrm{\barΩ}^{_+})$ are predicted. We discuss the rapidity distribution of net-baryon, and find that it reflects exactly the energy loss of colliding nuclei.

hep-ph↗