arXiv subjects

Qu-bing Xie

Publications and source records attributed to Qu-bing Xie.

15 recordsLinked to original sources

arXiv2012

Hadron Yield Correlation in Combination Models in High Energy AA Collisions

We study the hadron yield correlation in the combination models in high energy heavy ion collisions. We derive the relationship between the average yields of different hadrons produced in the combination of a system consisting of equal number of quarks and antiquarks. We present the results for the directly produced hadrons as well as those for the final hadrons including the strong and electromagnetic decay contributions. We also study the net quark influence by considering the case when the number of quarks is larger than that of the antiquarks. We make comparison with the data wherever possible.

hep-ph↗

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↗

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↗

arXiv2006

Charged-particle rapidity density in Au+Au collisions in a quark combination model

Rapidity/seudorapidity densities for charged particles and their centrality, rapidity and energy dependence in Au+Au collisions at RHIC are studied in a quark combination model. Using a Gaussian-type rapidity distribution for constituent quarks as a result of Landau hydrodynamic evolution, the data at $\sqrt{s_{NN}}=130, 200$ GeV at various centralities in full pseudorapidity range are well described, and the charged particle multiplicity are reproduced as functions of the number of participants. The energy dependence of the shape of the $dN_{ch}/dη$ distribution is also described at various collision energies $\sqrt{s_{NN}}=200, 130, 62.4$ GeV in central collisions with same value of parameters except 19.6 GeV. The calculated rapidity distributions and yields for the charged pions and kaons in central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV are compared with experimental data of the BRAHMS Collaboration.

nucl-th↗

arXiv2006

A study of elliptic flows in a quark combination model

We carry out a detail study of elliptic flows in Au-Au collisions at 200 AGeV in a quark combination model. We find that elliptic flow data for a variety of hadrons can be well reproduced except pions if constituent quarks with equal parallel transverse momenta combine into initially produced hadrons. In a combination mechanism where initial hadrons are formed by quarks with unequal parallel transverse momenta, theoretical predictions agree with data for all available hadrons including pions. The mass hierarchy at low transverse momenta in elliptic flows can be understood in the same quark combination mechanism as in the mediate range of transverse momenta.

nucl-th↗

arXiv2005

Production rates for hadrons, pentaquarks $Θ^+$ and $Θ^{*++}$, and di-baryon $(ΩΩ)_{0^{+}}$ in relativistic heavy ion collisions by a quark combination model

The hadron production in relativistic heavy ion collisions is well described by the quark combination model. The mixed ratios for various hadrons and the transverse momentum spectra for long-life hadrons are predicted and agree with recent RHIC data. The production rates for the pentaquarks $Θ^+$, $Θ^{*++}$ and the di-baryon $(ΩΩ)_{0^{+}}$ are estimated, neglecting the effect from the transition amplitude for constituent quarks to form an exotic state.

nucl-th↗

arXiv2003

Study of color connections in $e^+ e^-$ annihilation

We replace in the event generator JETSET the color singlet chain connection with the color separate state one as the interface between the hard and soft sectors of hadronic processes. The modified generator is applied to produce the hadronic events in $e^+ e^-$ annihilation. It describes the experimental data at the same level as the original JETSET with default parameters. This should be understood as a demonstration that color singlet chain is not the unique color connection. We also search for the difference in special sets of three-jet events arising from different color connections, which could subject to further experimental test.

hep-ph↗

arXiv2002

{Probing Colour Separate States in $e^+ e^-$ annihilation at $Z^0$ pole

Hadronic events in $e^+ e^- \to Z^0$ are generated by a Monte-Carlo model including the production of colour separate states. These events are compared with those produced by the JETSET with default set of parameters where the colour connections are colour singlet chains. By selecting two-jet-like events and a sensitive observable, we find that these two kinds of colour connections lead to significant differences in the hadronic states.

hep-ph↗

arXiv2001

Properties of color singlet chain states in $e^+e^-$ annihilation

We use the method of the color effective Hamiltonian to study the structure of color singlet chain states in $N_c=3$ and in the large $N_c$ limit. In order to obtain their total fraction when $N_c$ is finite, we illustrate how to orthogonalize these non-orthogonal states. We give numerical results for the fraction of orthogonalized states in $e^+e^-\to q\bar{q}gg$. With the help of a diagram technique, we derive their fraction up to $O(1/N_c^2)$ for the general multigluon process. For large $N_c$ the singlet chain states correspond to well-defined color topologies. Therefore we may expect that the fraction of non-color-singlet-chain states is an estimate of the fraction of events where color reconnection is possible. In the case of soft gluon bremsstrahlung, we give an explicit form for the color effective Hamiltonian which leads to the dipole cascade formulation for parton showering in leading order in $N_c$. The next-to-leading order corrections are also given for $e^+e^-\to q\bar{q}g_1g_2$ and $e^+e^-\to q\bar{q}g_1g_2g_3$.

hep-ph↗

arXiv2000

Color separate singlets in $e^+e^-$ annihilation

We use the method of color effective Hamiltonian to study the properties of states in which a gluonic subsystem forms a color singlet, and we will study the possibility that such a subsystem hadronizes as a separate unit. A parton system can normally be subdivided into singlet subsystems in many different ways, and one problem arises from the fact that the corresponding states are not orthogonal. We show that if only contributions of order $1/N_c^2$ are included, the problem is greatly simplified. Only a very limited number of states are possible, and we present an orthogonalization procedure for these states. The result is simple and intuitive and could give an estimate of the possibility to produce color separated gluonic subsystems, if no dynamical effects are important. We also study with a simple MC the possibility that configurations which correspond to "short strings" are dynamically favored. The advantage of our approach over more elaborate models is its simplicity, which makes it easier to estimate color reconnection effects in reactions which are more complicated than the relatively simple $e^+e^-$ annihilation.

hep-ph↗

arXiv1999

$e^{+}e^{-}\to Z^0Z^0\to b\bar{b}c\bar{c}$ events as model independent probe of colour reconnection effects

According to the basic properties of QCD, colour reconnection effects can occur in hadronic processes at high energies. The comparison of $e^{+}e^{-}\to Z^0Z^0\to q\bar{q}q'\bar{q'}$ events with the superposition of $Z^0\to q\bar{q}$ and $Z^0\to q'\bar{q'}$ events from LEP1 would provide an unambiguous model-independent probe. We show that at LEP2 energy, the background processes are negligible if we select only $e^{+}e^{-}\to Z^0Z^0\to b \bar{b}c\bar{c}$ events, and limit the measurements in the phase space of on-shell $Z^0Z^0$ events.

hep-ph↗

arXiv1999

Contribution of Colour-singlet Process $Υ\to J/Ψ+ c\bar{c}g$ to $Υ\to J/Ψ+ X$

We show that the colour-singlet process $Υ\to J/Ψ+ c\bar{c}g$ significantly contributes to the inclusive process $Υ\to J/Ψ+ X$. We calculate the partial width and the momentum distribution of the produced $J/Ψ$ in this channel. The obtained width is comparable to the experimental data. The momentum distribution is fairly soft, which is in contrast to the results from the colour-octet processes discussed earlier in literature but is consistent with the CLEO measurements. Further experiments to check this contribution are suggested.

hep-ph↗