Search

Using a quark combination model with the equal-velocity combination approximation, we study the production of hadrons with strangeness and charm flavor quantum numbers in Pb+Pb collisions at $\sqrt{s_{NN}}=$5.02 TeV. We present analytical expressions and numerical results for these hadrons' transverse momentum spectra and yield ratios. Our numerical results agree well with the experimental data available. The features of strange and charm hadron production in the quark--gluon plasma at the early stage of heavy ion collisions are also discussed., Comment: 12 pages, 9 figures

We compile experimental data for the averaged transverse momentum ($\left\langle p_{T}\right\rangle $) of proton, $\Lambda$, $\Xi^{-}$, $\Omega^{-}$ and $\phi$ at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}}=$ 200, 39, 27, 19.6, 11.5, 7.7 GeV and in Pb+Pb collisions at $\sqrt{s_{NN}}=$ 2.76 TeV, and find that experimental data of these hadrons exhibit systematic correlations. We apply a quark combination model with equal-velocity combination approximation to derive analytic formulas of hadronic $\left\langle p_{T}\right\rangle $ in the case of exponential form of quark $p_{T}$ spectra at hadronization. We use them to successfully explain the systematic correlations exhibited in $\left\langle p_{T}\right\rangle $ data of $p\Lambda$, $\Lambda\Xi^{-}$, $\Xi^{-}\Omega^{-}$ and $\Xi^{-}\phi$ pairs. We also use them to successfully explain the regularity observed in $\left\langle p_{T}\right\rangle $ of these hadrons as the function of $(dN_{ch}/dy)/(N_{part}/2)$ at mid-rapidity in central heavy-ion collisions at both RHIC and LHC energies. Our results suggest that the constituent quark degrees of freedom and the equal-velocity combination of these constituent quarks at hadronization play important role in understanding the production of baryons and $\phi$ meson at these RHIC and LHC energies., Comment: 10 pages, 7 figures

In this article, effects of electromagnetic field and asymmetric Gaussian potential (AGP) on the bound polaron’s low energy state in quantum well are explored theoretically by the Lee-Low-Pines unitary transformation and Pekar type variational method. The variation of the ground state energy and the first excited state energy of the polaron with the Coulomb bound potential (CBP) strength at different electron-phonon coupling (EPC) constants, electric field (EF) strengths, heights and ranges of the AGP and magnetic field adjustment lengths are obtained. Our numerical results indicate that the polaron’s low energy state depends on the EPC constant, the EF strength, the AGP’s height and range and the CBP strength.

The properties of the first excited state of a magnetopolaron in a patabolic quantum dot (PQD) are studied with the Lee-Low-Pines unitary transformation (LLPUT) and variational method of Pekar-type (VMPT). We find that the external magnetic field and the motion of the electron can trigger the Rashba effect in the first excited state and they play a virtual role in determining properties of the magnetopolaron in the parabolic PQD system. Furthermore, our results indicate the Rashba spin-orbit coupling(RSOC), confined potential, electron-phonon coupling, magnetic field and phonon wave vector promote a variation of the first excited state energy (FESE). In addition, the rule that the first excited state energy changes with one of four factors is not affected by the RSOC.

With the kinetic freeze-out nucleons and antinucleons obtained from the quark combination model, we study the production of light nuclei and antinuclei in the (anti-)nucleon coalescence mechanism in relativistic heavy ion collisions. We derive analytic formulas of the momentum distributions of different light nuclei and apply them to compute transverse momentum ($p_T$) spectra of (anti-)deuterons ($d$, $\bar d$) and (anti-)tritons ($t$, $\bar t$) in Au-Au collisions at $\sqrt{s_{NN}}=$7.7, 11.5, 19.6, 27, 39, 54.4 GeV. We find that the experimental data available for these $p_T$ spectra can be well reproduced. We further study the yields and yield ratios of different light (anti-)nuclei and naturally explain their interesting behaviors as a function of the collision energy. We especially point out that the multi-particle yield ratio $tp/d^2$ should be carefully corrected from hyperon weak decays for protons to probe the production characteristics of light nuclei. All of our results show that the coalescence mechanism for (anti-)nucleons plays a dominant role for the production of light nuclei and antinuclei at the RHIC beam energy scan energies., Comment: 14 pages,10 figures

We apply an equal-velocity quark combination model to study the production of light-flavor hadrons and single-charmed hadrons at midrapidity in $pp$ collisions at $\sqrt{s}=5.02$ TeV. We find experimental data for $p_{T}$ spectra of $\Omega$ and $\phi$ exhibit a quark number scaling property, which is a clear signal of quark combination mechanism at hadronization. Experimental data for $p_T$ spectra of $p$, $\Lambda$, $\Xi$, $\Omega$, $\phi$ and $K^{*0}$ are systematically described by the model. The non-monotonic $p_{T}$ dependence of $\Omega/\phi$ ratio is naturally explained and we find it is closely related to the shape of the logarithm of strange quark $p_{T}$ distribution. Using $p_{T}$ spectra of light-flavor quarks obtained from light-flavor hadrons and a $p_T$ spectrum of charm quarks which is consistent with perturbative QCD calculations, the experimental data for differential cross-sections of $D^{0,+}$, $D_{s}^{+}$ and $\Lambda_{c}^{+}$ as the function of $p_{T}$ are systematically described. We predict the differential cross-sections of $\Xi_{c}^{0,+}$ and $\Omega_{c}^{0}$. The ratio $\Xi_{c}^{0,+}/D^{0}$ in our model is about 0.16 and $\Omega_{c}^{0}/D^{0}$ is about 0.012 due to the cascade suppression of strangeness. In addition, the predicted $\Xi_{c}^{0,+}/D^{0}$ and $\Omega_{c}^{0}/D^{0}$ ratios exhibit the non-monotonic dependence on $p_{T}$ in the low $p_{T}$ range. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.

We study the momentum dependence of the production of light nuclei in high-energy collisions in the nucleon coalescence mechanism. We derive formulas of the momentum distributions of deuterons $d$ and helions $^{3}\mathrm{He}$. We obtain the analytic expressions of the coalescence factor ${B}_{A}$ (${B}_{2}$ for $d$ and ${B}_{3}$ for $^{3}\mathrm{He}$) as functions of the collision system size and the momentum. We apply the deduced results to $p\ensuremath{-}p$, $p$-Pb and Pb-Pb collisions to explain naturally the interesting behavior of ${B}_{A}$ observed in experiments at the CERN Large Hadron Collider.

In the present work, we study the influences of the temperature and the Rashba spin-orbit interaction on the oscillation period of the bound polaron in the quantum pseudodot using the Lee-Low-Pines unitary transformation, the variational method of Pekar-type and the quantum statistical theory. We have derived the oscillation period of the bound polaron in the superposition state and reported the temperature dependences and the Rashba spin-orbit interaction effects of the oscillation period of polaron when the wave vector, the electron-LO phonon coupling, the Coulomb bound potential and the chemical potential take different values.

We apply a quark combination model to study yield densities and transverse momentum (${p}_{T}$) spectra of strange (anti)hadrons at midrapidity in central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=7.7$, 11.5, 19.6, 27, 39, and 200 GeV. We show that the experimental data for ${p}_{T}$ spectra of (anti)hadrons in these collisions can be systematically described by the equal velocity combination of constituent quarks and antiquarks at hadronization. We obtain the ${p}_{T}$ spectra of quarks and antiquarks at hadronization and study their collision energy dependence. We also reproduce the yield densities of hadrons and antihadrons. In particular, we demonstrate that the yield ratios of antihadrons to hadrons ${K}^{\ensuremath{-}}/{K}^{+}, \overline{p}/p, \overline{\mathrm{\ensuremath{\Lambda}}}/\mathrm{\ensuremath{\Lambda}}, {\overline{\mathrm{\ensuremath{\Xi}}}}^{+}/{\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}$, and ${\overline{\mathrm{\ensuremath{\Omega}}}}^{+}/{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}$ simply correlate with each other and their experimental data except ${\overline{\mathrm{\ensuremath{\Omega}}}}^{+}/{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}$ at $\sqrt{{s}_{NN}}=7.7$ GeV are systematically described by the model. These results suggest that the equal velocity combination mechanism for quarks and antiquarks at hadronization plays an important role for the production of these long-lived hadrons in $\mathrm{Au}+\mathrm{Au}$ collisions at low RHIC energies ($\sqrt{{s}_{NN}}\ensuremath{\ge}11.5$ GeV).

We apply a quark combination model with equal-velocity combination (EVC) approximation to study the elliptic flow ($v_{2}$) of hadrons in heavy-ion collisions in a wide collision energy range ($\sqrt{s_{NN}}=$ 27 - 5020 GeV). Utilizing the simple relationship between $v_{2}$ of hadrons and those of quarks under EVC, we find that $v_{2}$ of up/down quarks obtained by experimental data of proton is consistent with that obtained by data of $\Lambda$ and $\Xi$. $v_{2}$ of strange quarks obtained by data of $\Omega$ is consistent with that obtained by data of $\Lambda$ and $\Xi$, and at RHIC energies it is also consistent with that obtained by data of $\phi$. This means that $v_{2}$ of these hadrons have a common quark-level source. Using data of $D^0$, we obtain $v_{2}$ of charm quarks with $p_T\lesssim 6$ GeV/c. We find that under EVC charm quark dominates $v_{2}$ of $D$ mesons at low $p_{T}$ but light-flavor quarks significantly contribute to $v_{2}$ of $D$ mesons in the range $3\lesssim p_{T}\lesssim8$ GeV/c. We predict $v_{2}$ of charmed baryons $\Lambda_{c}^{+}$ and $\Xi_{c}^{0}$ which show a significant enhancement at intermediate $p_{T}$ due to the double contribution of light-flavor quarks. The properties of the obtained quark $v_{2}$ under EVC are studied and a regularity for $v_{2}$ of quarks as the function of $p_{T}/m$ is found., Comment: 12 pages, 11 figures

We show that the experimental data of transverse momentum ($p_{T}$) spectra of $\Omega$ baryon and $\phi$ meson at mid-rapidity in heavy-ion collisions exhibit the constituent quark number scaling in a wide energy range from RHIC to LHC. Such a scaling behavior is a direct consequence of quark combination mechanism via equal velocity combination and provides a very convenient way to extract the $p_{T}$ spectrum of strange quarks at hadronization. We present the results of strange quarks obtained from the available data and study the properties in particular the energy dependence of the averaged transverse momentum $\langle p_{T}\rangle$ and the transverse radial flow velocity $\langle\beta\rangle$ with a hydrodynamics-motivated blast-wave model.

Recent data on the production of $D$ mesons and $\Lambda_c^+$ baryons in heavy ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider exhibit a number of striking characteristics such as enhanced yield ratios $D_s^+/D^0$, $\Lambda_c^+/D^0$ and their transverse momentum dependences. In this paper, we derive the momentum dependence of open charm mesons and singly charmed baryons produced in ultra-relativistic heavy ion collisions via the equal-velocity quark combination. We present analytic expressions and numerical results of yield ratios and compare them with the experimental data available. We make predictions for other charmed hadrons., Comment: 2 tables, 8 figures

We study the property of magnetopolaron in a parabolic quantum dot under the Rashba spin–orbit interaction (RSOI) by adopting an unitary transformation of Lee–Low–Pines type and the variational method of Pekar type with and without considering the temperature. The temporal spatial distribution of the probability density and the relationships of the oscillating period with the RSOI constant, confinement constant, electron–phonon coupling strength, phonon wave vector and temperature are discussed. The results show that the probability density of the magnetopolaron in the superposition of the ground and first excited state takes periodic oscillation (T 0/period) in the presence or absence of temperature. Because of the RSOI, the oscillating period is divided into different branches. Also, the results indicate that the oscillating period increases (decreases) when the RSOI constant, electron-phonon coupling strength and phonon wave vector (the confinement constant) increase in a proper temperature, and the temperature plays a significant role in determining the properties of the polaron.

We show that the experimental data of transverse momentum ( p T ) spectra of identified hadrons released recently by ALICE collaboration for p–Pb collisions at s N N = 5.02 TeV exhibit a distinct universal behavior — the quark number scaling. We further show that the scaling is a direct consequence of quark (re-)combination mechanism of hadronization and can be regarded as a strong indication of the existence of the underlying source with constituent quark degree of freedom for the production of hadrons in p–Pb collisions at such high energies. We make also predictions for production of other hadrons.

We present a new method of solving the probability distribution for baryons, antibaryons and mesons at the hadronization of 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 use the method of the generating function to derive the outcome of the quark combination rule, which is much simpler and easier to be generalized than the original method. Furthermore, we use the formula of the quark combination rule and its generalization to study the property of 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 quark combination model in studying hadronic multiplicity fluctuations and the underlying phase transition property in relativistic heavy-ion collisions., 17 pages, 3 figures. To be published in Chinese Physics C

We show that the spectra of and at midrapidity in the inelastic events in 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 collisions at = 13 TeV. The midrapidity spectra for protons, , , , and 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 dependence of the ratio 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 spectra of strange hadrons at midrapidity in different multiplicity classes in collisions at 13 TeV are predicted for further tests of the model. The midrapidity spectra of soft ( GeV/c) strange quarks and up/down quarks at hadronization in collisions at 13 TeV are extracted.

If quark-gluon plasma (QGP)--like medium is created in $p$-Pb collisions at extremely high collision energies, charm quarks that move in the medium can hadronize by capturing the comoving light quark(s) or antiquark(s) to form the charm hadrons. Using light quark ${p}_{T}$ spectra extracted from the experimental data of light-flavor hadrons and a charm quark ${p}_{T}$ spectrum that is consistent with perturbative QCD calculations, the central-rapidity data of ${p}_{T}$ spectra and the spectrum ratios for $D$ mesons in the low-${p}_{T}$ range (${p}_{T}\ensuremath{\lesssim}7$ GeV/$c$) in minimum-bias $p$-Pb collisions at $\sqrt{{s}_{NN}}=5.02$ TeV are well described by the quark combination mechanism in equal-velocity combination approximation. The ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}/{D}^{0}$ ratio in quark combination mechanism exhibits the typical increase-peak-decrease behavior as the function of ${p}_{T}$, and the shape of the ratio for ${p}_{T}\ensuremath{\gtrsim}3$ GeV/$c$ is in agreement with the data of the ALICE Collaboration in central rapidity region $\ensuremath{-}0.96lyl0.04$ and the preliminary data of the LHCb Collaboration in forward rapidity region $1.5lyl4.0$. The global production of single-charm baryons is quantified using the data and the possible enhancement (relative to light flavor baryons) is discussed. The ${p}_{T}$ spectra of ${\mathrm{\ensuremath{\Xi}}}_{c}^{0}, {\mathrm{\ensuremath{\Omega}}}_{c}^{0}$ in minimum-bias events and those of single-charm hadrons in high-multiplicity event classes are predicted, which serves as the further test of the possible change of the hadronization characteristic for low-${p}_{T}$ charm quarks in the small system created in $p$-Pb collisions at Large Hadron Collider energies.

Treating the light-flavor constituent quarks and antiquarks whose momentum information is extracted from the data of soft light-flavor hadrons in pp collisions at $$\sqrt{s}=7$$ s=7 TeV as the underlying source of chromatically neutralizing the charm quarks of low transverse momenta ($$p_{T}$$ pT ), we show that the experimental data of $$p_{T}$$ pT spectra of single-charm hadrons $$D^{0,+}$$ D0,+ , $$D^{*+}$$ D∗+ $$D_{s}^{+}$$ Ds+ , $$\varLambda _{c}^{+}$$ Λc+ and $$\varXi _{c}^{0}$$ Ξc0 at mid-rapidity in the low $$p_{T}$$ pT range ($$2\lesssim p_{T}\lesssim 7$$ 2≲pT≲7 GeV/c) in pp collisions at $$\sqrt{s}=7$$ s=7 TeV can be well understood by the equal-velocity combination of perturbatively created charm quarks and those light-flavor constituent quarks and antiquarks. This suggests a possible new scenario of low $$p_{T}$$ pT charm quark hadronization, in contrast to the traditional fragmentation mechanism, in pp collisions at LHC energies. This is also another support for the exhibition of the soft constituent quark degrees of freedom for the small parton system created in pp collisions at LHC energies.

Treating the light-flavor constituent quarks and antiquarks that can well describe the data of light-flavor hadrons in $pp$ collisions at $\sqrt{s}=7$ TeV as the underlying source of chromatically neutralizing the charm quarks of low transverse momenta ($p_{T}$), we show that the experimental data of $p_{T}$ spectra of single-charm hadrons $D^{0,+}$, $D^{*+}$ $D_{s}^{+}$, $\Lambda_{c}^{+}$ and $\Xi_{c}^{0}$ at mid-rapidity in the low $p_{T}$ range ($2\lesssim p_{T}\lesssim7$ GeV/$c$) in $pp$ collisions at $\sqrt{s}=7$ TeV can be well understood by the equal-velocity combination of perturbatively-created charm quarks and those light-flavor constituent quarks and antiquarks. This suggests a possible new scenario of low $p_{T}$ charm quark hadronization, in contrast to the traditional fragmentation mechanism, in $pp$ collisions at LHC energies. This is also another support for the exhibition of the effective constituent quark degrees of freedom for the small parton system created in $pp$ collisions at LHC energies.

We show that the experimental data of midrapidity ${p}_{T}$ spectra for $p$, $\mathrm{\ensuremath{\Lambda}}$, $\mathrm{\ensuremath{\Xi}}$, ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}$, ${\mathrm{K}(892)}^{*0}$, and $\mathrm{\ensuremath{\Xi}}(1530{)}^{*0}$ in minimum-bias $pp$ collisions at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ can be well fitted by the quark combination mechanism with the parametrized up(down) quark spectrum and strange quark spectrum at hadronization. The averaged transverse momentum $⟨{p}_{T}⟩$ and spectrum ratios such as $\mathrm{\ensuremath{\Xi}}/\mathrm{\ensuremath{\Lambda}}$ and $\mathrm{\ensuremath{\Omega}}/\ensuremath{\phi}$ calculated from quark combination reproduce the data quite well. The available data of hadronic ${p}_{T}$ spectra released by ALICE collaboration in the first three high-multiplicity classes of $pp$ collisions at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ are also well fitted. The extracted quark spectra at hadronization exhibit a dependence on the multiplicity class and also show a certain similarity to those obtained in $p\text{\ensuremath{-}}\mathrm{Pb}$ collisions at LHC and in relativistic heavy ion collisions. We make predictions for other hadrons, and propose two scaling behaviors among decuplet baryons and vector mesons as the effective probe of hadron production mechanism at such high collision energies.

We propose a new method, i.e., an exclusive quark combination model + an inclusive hadron recombination model, to study different production sources of light nuclei in relativistic heavy-ion collisions. We take deuterons and $^3$He produced in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV as examples to present contributions of different production sources by studying their rapidity densities $dN/dy$, yield ratios and transverse momentum ($p_T$) spectra just after the hadronization as well as at the final kinetic freeze-out. We find that: only very small fractions of $d$ and $^3$He are created just after the hadronization; nucleons from $\Delta$ resonance decays make a much larger contribution to the regeneration of light nuclei at the hadronic phase stage, and this contribution takes about 79\% and 92\% for $d$ and $^3$He, respectively, observed at the final kinetic freeze-out. We also find that yield ratios $d/p$, $^3$He$/p$ and $^3$He$/d$ are good observables to probe contributions for light nuclei from different production sources, and provide a natural explanation for constant values of $d/p$ and $^3$He$/p$ as a function of the averaged charged multiplicity measured by the ALICE Collaboration., Comment: 12 pages, 2 figures

We study the multiplicity fluctuation and correlation of identified mesons and baryons formed at the 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 such as 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 $\nu_{dyn}$ for $\text{K}\pi$, $p\pi$ and $\text{K}p$ pairs and discuss what underlying physics can be obtained by comparing with the data in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV and the simulations from HIJING and AMPT event generators., Comment: 8 pages, 3 figures

Yield ratios of identified hadrons observed in high multiplicity p+p and p+Pb collisions at LHC show remarkable similarity with those in Pb+Pb collisions, indicating some important and universal underlying dynamics in hadron production for different quark gluon final states. We use the quark combination model to explain the data of yield ratios in these three collision systems. The observed $p/\pi$ and $\Lambda/K_s^0$ can be reproduced simultaneously by quark combination, and these two ratios reflect the rate of baryon production at hadronization which is the same in light sector and strange sector and is roughly constant in p+p, p+Pb and Pb+Pb collision systems over three orders of magnitude in charged particle multiplicity.The data of $K_s^0/\pi$, $\Lambda/\pi$, $\Xi/\pi$ and $\Omega/\pi$ show a hierarchy behavior relating to the strangeness content, and are naturally explained by quark combination both in the saturate stage at high multiplicity and in the increase stage at moderate multiplicity. Our results suggest that the dynamical characteristic of quark combination is necessary in describing the production of hadrons in small systems created in p+p and p+Pb collisions.

The dynamical fluctuation and correlation of multiplicity distributions of identified baryons and antibaryons produced by the hadronization of the bulk quark system are systematically studied in quark combination model. Starting from the most basic dynamics of quark combination which are necessary for multiplicity study, we analyze moments (variance, skewness and kurtosis) of inclusive multiplicity distribution of identified baryons, two-baryon multiplicity correlations, and baryon-antibaryon multiplicity correlations after the hadronization of quark system with given quark number and antiquark number. We obtain a series of interesting findings, e.g., binomial behavior of multiplicity moments, coincide flavor dependent two-baryon correlation and universal baryon-antibaryon correlation, which can be regarded as general features of quark combination. We further take into account correlations and fluctuations of quark numbers before hadronization to study their influence on multiple production of baryons and antibaryons. We find that quark number fluctuation and flavor conservation lead to a series of important results such as the negative $p\bar{\Omega}^{+}$ multiplicity correlation and universal two-baryon correlations. We also study the influence of resonance decay in order to compare our results with future experimental data in ultra-relativistic heavy ion collisions at LHC., Comment: 19 pages, 12 figures

We study the probability density and the excitation energy of the bound polaron in the quantum pseudodot under the Rashba spin–orbit interaction by using the unitary transformation of Lee–Low–Pines and the variational method of Pekar. The results of a numerical calculation show that the probability density of the bound polaron in the superposition state is periodic and oscillates with the period T 0 . Due to the Rashba spin–orbit interaction, the excitation energy splits into different branches. It also can be seen that the excitation energy changes with the phonon wave vector when the two-dimensional electron gas’s chemical potential, the electron–LO phonon coupling, the Coulomb bound potential and the Rashba coupling parameter take different values.

In the framework of the quark combination, we derive the yield formulas and study the yield ratios of hidden-charm pentaquark states in ultrarelativistic heavy ion collisions. We propose some interesting yield ratios which clearly exhibit the production relationships between different hidden-charm pentaquark states. We show how to employ a specific quark combination model to evaluate the yields and predict the transverse momentum (${p}_{T}$) spectra of exotic ${P}_{c}^{+}(4380), {P}_{c}^{+}(4450)$, and their partners as pentaquark states on the basis of reproducing the yields and ${p}_{T}$ spectra of normal identified hadrons and execute the calculations in central Pb + Pb collisions at $\sqrt{{s}_{NN}}=2.76$ TeV as an example.

The production of hadronic resonances $K^{*}(892)$, $\phi(1020)$, $\Sigma^{*}(1385)$, and $\Xi^{*}(1530)$ in central AA collisions at $\sqrt{s_{NN}}=$ 17.3, 200, and 2760 GeV are systematically studied. The direct production of these resonances at system hadronization are 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 $p_T$ spectra of $K^{*}(892)$ calculated directly by quark combination model are explicitly higher than the data at low $p_T \lesssim 1.5$ 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 $\phi(1020)$ 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 $p_T$ spectra of $\Sigma^{*}(1385)$ and $\Xi^{*}(1530)$ to be tested by the future experimental data., Comment: 5 pages, 6figures

To date, the nature of ${Z}_{c}(3900)/{Z}_{c}(4025)$ is not clear. In this work, we propose to study the internal structure of ${Z}_{c}(3900)/{Z}_{c}(4025)$ by exploring the charmless decays. Compared to charmed decays, charmless decay channels may play a unique role since they request the annihilation of the heavy constituents. We calculate the decay width for ${Z}_{c}(3900)/{Z}_{c}(4025)\ensuremath{\rightarrow}VP$, where $P$ and $V$ denote the pseudoscalar and light vector meson, respectively. Here, the ${Z}_{c}(3900)$ and ${Z}_{c}(4025)$ are the molecular states of ${D}^{*}\overline{D}$ and ${D}^{*}{\overline{D}}^{*}$. The decay process occurs through intermediate $D{D}^{*}/{D}^{*}{D}^{*}$ meson loops. Based on an effective Lagrangian, we obtain sizable predictions for the branching ratios, which are accessible in experiments. The experimental measurements in the future will not only shed light on the decay mechanism but will also lead to a deeper understanding of the mysterious structure of the ${Z}_{c}(3900)/{Z}_{c}(4025)$.

The elliptic flows of identified hadrons in Au + Au collisions at [Formula: see text] are systematically investigated within the framework of quark (re)combination/coalescence. The results indicate that the quark combination mechanism can describe self-consistently the elliptic flows of various hadrons from low to intermediate pT range.

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 $\pi^{\pm}$, $K^{\pm}$, $p(\bar{p})$ and net protons $(p-\bar{p})$ are well described. We also predict rapidity distributions for $K^{0}_{s}$, $\Lambda(\bar{\Lambda})$, $\mathrm{\Xi^{-}}$ ($\mathrm{\bar{\Xi}^{_+}}$) and $\mathrm{\Omega^{-}}+\mathrm{\bar{\Omega}}^{_+}$. The multiplicity ratios of charged antihadrons to hadrons as a function of rapidity are reproduced. The results for ${p}_{T}$ spectra of $\pi^{\pm}$, $K^{\pm}$, $p(\bar{p})$ and for the $p/\pi$ ratios in a broader ${p}_{T}$ range agree well with the data. Finally the rapidity dependence of transverse momentum distributions for hadrons are given.

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 $dN_{ch}/d\eta$ 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 $dN/d\eta$ 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 $dN_{ch}/d\eta/|_{\eta\approx0}$ as function of $\sqrt{s_{NN}}$ and $N_{part}$ from RHIC to LHC., Comment: 12 pages, 8 figures

The baryon-strangeness correlation in the hadronization of quark matter is studied within the quark combination mechanism. We calculate the correlation coefficient ${C}_{BS}=\ensuremath{-}3\left(\ensuremath{\langle}BS\ensuremath{\rangle}\ensuremath{-}\ensuremath{\langle}B\ensuremath{\rangle}\ensuremath{\langle}S\ensuremath{\rangle}\right)/\left(\ensuremath{\langle}{S}^{2}\ensuremath{\rangle}\ensuremath{-}{\ensuremath{\langle}S\ensuremath{\rangle}}^{2}\right)$ of initial hadrons produced from the deconfined free quark system with ${C}_{BS}^{(q)}=1$. The competition of the production of baryons against that of mesons is the key dynamics that is most relevant to the change of baryon-strangeness correlation during system hadronization. Results of quark combination under the Poisson statistics agree with the statistical model predictions for a hadron resonance gas at vanishing chemical potential but differ from those at relatively large chemical potentials. Results beyond Poisson statistics are also obtained and are compared with calculations of lattice QCD in the quark-hadron phase boundary. We predict the dependence of the ${C}_{BS}$ of the hadron system on the baryon chemical potential and strangeness. These predictions are expected to be tested by future lattice QCD calculations at nonzero chemical potentials and/or by the Beam Energy Scan experiment of the STAR Collaboration at RHIC.

Recently the ALICE Collaboration has published a few data of charm hadrons in Pb + Pb collisions at the CERN Large Hadron Collider (LHC). We extend the quark combination to the charm sector and point out that the measurement of charm hadron yields can provide important insights into charm quark hadronization mechanism and properties of the hot and dense matter produced in high energy reactions. We propose several types of yield ratios, e.g. $D^{*+}/D^0$, $D_s^+/D^+$ and $\Lambda_c^+/D_s^+$, to measure various properties of low $p_T$ charm quark hadronization. We argue that ratios $D_s^+/D^0$ and $2D_s^+/(D^0+D^+)$ as the function of transverse momentum can serve as good probes for the dynamics of charm quark hadronization. We further make predictions for the yields and $p_T$ spectra of identified charm hadrons in central Pb + Pb collisions at $\sqrt{s_{NN}}= 2.76$ TeV.

We extend the study of hadron yield correlation in combination models in a recent publication to baryon-anti-baryon flavor correlations in heavy ion collisions. We show that the universal behaviors of the anti-baryon to baryon yield ratios as functions of that of $K^-$ to $K^+$ are naturally explained. We study also the "mixed ratios" and propose other measurements that might be sensitive to the hadronization mechanism., 4 pages, 4 figures

Radiative transitions between charmonium states offer an insight into the internal structure of heavy quark bound states within QCD. In this work, we systematically investigate the coupled-channel effects of intermediate charmed mesons to charmonium radiative transitions utilizing an effective Lagrangian approach. Our results show that the coupled-channel effects of these decays under the open charm thresholds are relatively weak, while the coupled-channel effects of the excited P-wave states close to the charmed pairs thresholds are relatively important.

Experimental data at RHIC and SPS energies suggest a systematic correlation between yield ratio $\bar{p}/p$ and $K^{-}/K^{+}$, which reveal some universality of hadron production in relativistic heavy ion collisions. We propose an explanation based on the quark combination mechanism in which the production asymmetry between baryons and antibaryons is focused on especially. We start from the basic ideas of quark combination to carry out a general analysis of the properties of the global production of baryons and mesons and obtain the yields of baryons, antibaryons and mesons as functions of the number of constituent quarks and antiquarks just before hadronization. In particular, we study effects of quark-antiquark asymmetry on the ratio of (anti-)baryons to mesons and that of antibaryons to baryons. We use these formula to well explain the data of $\bar{p}/p$ and $K^{-}/K^{+}$ at different of collision energies and rapidities and suggest further measurements at moderate RHIC energies in the mid-forward rapidity regions to make the decisive test of this universality., Comment: 5 pages, 2 figures