Hadronic rapidity spectra in heavy ion collisions at SPS and AGS energies in a quark combination model

The quark combination mechanism of hadron production is applied to nucleus-nucleus collisions at the CERN Super Proton Synchrotron （SPS） and the BNL Alternating Gradient Synchrotron （AGS）.The rapidity spectra of identified hadrons and their spectrum widths are studied.The data of π -,K±,φ,Λ,Λ,Ξ - and Ξ＋ at 80 and 40 A GeV,and in particular at 30 and 20 A GeV where the onset of deconfinement is suggested to happen,are consistently described by the quark combination model.However,at AGS 11.6 A GeV below the onset,the π±,K±and Λ spectra cannot be simultaneously explained,indicating the disappearance of the intrinsic correlation of their production in the constituent quark level.The collision-energy dependence of the rapidity spectrum widths of the constituent quarks,and the strangeness of the hot and dense quark matter produced in heavy ion collisions,are obtained and discussed.

Statistical method in quark combination model

We present a new method for solving the probability distribution for baryons,antibaryons,and mesons at the hadronization of the constituent quark and antiquark system.The hadronization is governed by the quark combination rule in the quark combination model developed by the Shandong Group.We employ the method of the generating function to derive the outcome of the quark combination rule,which is significantly simpler and easier to generalize than the original method.Furthermore,we use the formula of the quark combination rule and its generalization to study the property of the multiplicity distribution of net-protons.Taking a naive case of quark number fluctuations and correlations at hadronization,we calculate ratios of multiplicity cumulants of final-state net-protons and discuss the potential applicability of the quark combination model by studying hadronic multiplicity fluctuations and the underlying phase transition property in relativistic heavy-ion collisions.

An explanation for deviations from the quark number scaling of elliptic flows in low P_T region

We carry out a systematic study of the different contributions to the deviations of the elliptic flows from the quark number scaling in high energy heavy ion collision in a quark combination model. The effects that we considered are： the resonance decay, the flavor dependence of the quark elliptic flow and the combination of quarks/antiquarks with slightly different transverse momenta. Our results show that the deviations observed in experiments can be well reproduced within the combination framework if all the three effects are considered. We make a detailed analysis of the different contributions using a Monte-Carlo program and suggest measuring the quark number scaling in intermediate PT range more precisely.

Constituent quark number scaling from strange hadron spectra in pp collisions at ■=13 TeV

We show that the p_T spectra ofΩ^-andφat midrapidity in the inelastic events in pp collisions at■=13 TeV exhibit a constituent quark number scaling property,which is a clear signal of quark combination mechanism at hadronization.We use a quark combination model with equal velocity combination approximation to systematically study the production of identified hadrons in pp collisions at■=13 TeV.The midrapidity spectra for protons,∧,Ξ^-,Ω^-,φand K~*in the inelastic events are simultaneously fitted by the model.The multiplicity dependence of the yields of these hadrons are also well understood.The strong p_T dependence of the p/φratio is well explained by the model,which further suggests that the production of two hadrons with similar masses is determined by their quark content at hadronization.The p_T spectra of strange hadrons at midrapidity in different multiplicity classes in pp collisions at■=13 TeV are predicted for further tests of the model.The midrapidity p_T spectra of soft(p_T<2 GeV/c)strange quarks and up/down quarks at hadronization in pp collisions at■=13 TeV are extracted.

Centrality dependence of pT spectra for identified hadrons in Au+Au and Cu+Cu collisions at (~SNN)^(1/2)=200 GeV

The centrality dependence of transverse momentum spectra for identified hadrons at midrapidityin Au＋Au collisions at √sNN=200GeV is systematically studied in a quark combination model. The PTspectra of π^±, K^±, p（p） and A（A） in different centrality bins and the nuclear modification factors （Rcp） forthese 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 smallerCu＋Cu collision system. The centrality dependence of PT spectra and the Rcp for π^0, Ks^0 and A in Cu-bCucollisions at √sNN = 200 GeV are well described. The results show that （β （r）〉is only a function of the numberof participants Npart and it is independent of the collision system.

Rapidity dependence of hadron p_T spectra in central Au+Au collisions at s_(NN)～(1/2)=200 GeV

The transverse momentum spectra for identified hadrons at different rapidities in central Au＋Au collisions at √^SNN= 200 GeV are studied in a quark combination model. The results for PT spectra of π^±, K^±, p（p^-） and for the p/π ratios in a broader PT range at midrapidity agree well with the data. The transverse momentum spectra of pions, protons and antiprotons at various rapidities y - 1, η= 2.2 and y ≈ 3.2 are calculated and compared with the data.

Energy dependence of resonance production in relativistic heavy ion collisions

The production of the hadronic resonances K^＊0（892）,φ（1020）,∑^＊（1385）,and Ξ^＊（1530） in central AA collisions at √SNN=17.3,200,and 2760 GeV is systematically studied.The direct production of these resonances at system hadronization is described by the quark combination model and the effects of hadron multiple-scattering stage are dealt with by a ultra-relativistic quantum molecular dynamics model（UrQMD）.We study the contribution of these two production sources to final observation and compare the final spectra with the available experimental data.The pT spectra of K^＊0（892） calculated directly by quark combination model are explicitly higher than the data at low pT≤1.5 GeV,and taking into account the modification of rescattering effects,the resulting final spectra well agree with the data at all three collision energies.The rescattering effect on φ（1020） production is weak and including it can slightly improve our description at low p_T on the basis of overall agreement with the data.We also predict the pT spectra of ∑^＊（1385） and Ξ^＊（1530）,to be tested by the future experimental data.

Multiplicity fluctuation and correlation of mesons and baryons in ultra-relativistic heavy-ion collisions at the LHC

We study the multiplicity fluctuation and correlation of identified mesons and baryons formed at hadronization by the quark combination mechanism in the context of ultra-relativistic heavy-ion collisions. Based on the statistical method of free quark combination, we derive the two-hadron multiplicity correlations, including meson-meson and meson-baryon correlations, and take the effects of quark number fluctuation at hadronization into account by a Taylor expansion method. After including the decay contributions, we calculate the dynamical fluctuation observable ν_（dyn） for Kπ, pπ and Kp pairs and discuss what underlying physics can be obtained by comparing with data from Pb-Pb collisions at sNN^（1/2）=2.76 Te V and simulations from the HIJING and AMPT event generators.