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Register a new userImproved Quark Coalescence for a Multi-Phase Transport Model
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The string melting version of a multi-phase transport model is often applied to high-energy heavy-ion collisions since the dense matter thus formed is expected to be in parton degrees of freedom. In this work we improve its quark coalescence component, which describes the hadronization of the partonic matter to a hadronic matter. We removed the previous constraint that forced the numbers of mesons, baryons, and antibaryons in an event to be separately conserved through the quark coalescence process. A quark now could form either a meson or a baryon depending on the distance to its coalescence partner(s). We then compare results from the improved model with the experimental data on hadron $dN/dy$, $p_{_{rm T}}$ spectra, and $v_2$ in heavy-ion collisions from $sqrt{s_{_{rm NN}}}=62.4$ GeV to $5.02$ TeV. We show that, besides being able to describe these observables for low-$p_{_{rm T}}$ pions and kaons, the improved model also better describes the low-$p_{_{rm T}}$ baryon observables in general, especially the baryon $p_{_{rm T}}$ spectra and antibaryon-to-baryon ratios for multistrange baryons.
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Initial partonic eccentricities in Au+Au collisions at center-of-mass energy $sqrt{s_{NN}}$ = 200 GeV are investigated using a multi-phase transport model with string melting scenario. The initial eccentricities in different order of harmonics are studied using participant and cumulant definitions. Eccentricity in terms of second-, fourth- and sixth order cumulants as a function of number of participant nucleons are compared systematically with the traditional participant definition. The ratio of the cumulant eccentricities $varepsilonleft{4right}/varepsilonleft{2right}$ and $varepsilonleft{6right}/varepsilonleft{4right}$ are studied in comparison with the ratio of the corresponding flow harmonics. The conversion coefficients ($v_n/varepsilon_n$) are explored up to fourth order harmonic based on cumulant method. Furthermore, studies on transverse momentum ($p_T$) and pseudo-rapidity ($eta$) dependencies of eccentricities and their fluctuations are presented. As in ideal hydrodynamics initial eccentricities are expected to be closely related to the final flow harmonics in relativistic heavy-ion collisions, studies of the fluctuating initial condition in the AMPT model will shed light on the tomography properties of the initial source geometry.
We study the production of charmed hadrons $D^{0}$ and $Lambda_c^+$ in relativistic heavy-ion collisions using an improved quark coalescence model. In particular, we extend the usual coalescence model by letting a produced hadron to have the same velocity as the center-of-mass velocity of coalesced constituent quarks during hadronization to take into account the effect of collective flow in produced quark-gluon plasma. This results in a shift of charmed resonances of higher masses to larger transverse momenta ($p_T^{}$). Requiring all charm quarks of very low $p_T^{}$ to be converted to hadrons via coalescence and letting charm quarks not undergoing coalescence to hadronize by independent fragmentation, we obtain a good description of the measured yield ratio $Lambda_c^+/D^0$ as a function of $p_T^{}$ in $text{Au} + text{Au}$ collisions at $sqrt{s_{NN}}^{}=200$~GeV by the STAR Collaboration at the Relativistic Heavy Ion Collider.
We propose an improved quark coalescence model for spin alignment of vector mesons and polarization of baryons by spin density matrix with phase space dependence. The spin density matrix is defined through Wigner functions. Within the model we propose an understanding of spin alignments of vector mesons $phi$ and $K^{*0}$ (including $bar{K}^{*0}$) in the static limit: a large positive deviation of $rho_{00}$ for $phi$ mesons from 1/3 may come from the electric part of the vector $phi$ field, while a negative deviation of $rho_{00}$ for $K^{*0}$ may come from the electric part of vorticity tensor fields. Such a negative contribution to $rho_{00}$ for $K^{*0}$ mesons, in comparison with the same contribution to $rho_{00}$ for $phi$ mesons which is less important, is amplified by a factor of the mass ratio of strange to light quark times the ratio of $leftlangle mathbf{p}_{b}^{2}rightrangle $ on the wave function of $K^{*0}$ to $phi$ ($mathbf{p}_{b}$ is the relative momentum of two constituent quarks of $K^{*0}$ and $phi$). These results should be tested by a detailed and comprehensive simulation of vorticity tensor fields and vector meson fields in heavy ion collisions.
Both hydrodynamics-based models and a multi-phase transport (AMPT) model can reproduce the mass splitting of azimuthal anisotropy ($v_n$) at low transverse momentum ($p_{perp}$) as observed in heavy ion collisions. In the AMPT model, however, $v_n$ is mainly generated by the parton escape mechanism, not by the hydrodynamic flow. In this study we provide detailed results on the mass splitting of $v_n$ in this transport model, including $v_2$ and $v_3$ of various hadron species in d+Au and Au+Au collisions at the Relativistic Heavy Ion Collider and p+Pb collisions at the Large Hadron Collider. We show that the mass splitting of hadron $v_2$ and $v_3$ in AMPT first arises from the kinematics in the quark coalescence hadronization process, and then, more dominantly, comes from hadronic rescatterings, even though the contribution from the latter to the overall charged hadron $v_n$ is small. We further show that there is no qualitative difference between heavy ion collisions and small-system collisions or between elliptic ($v_2$) and triangular ($v_3$) anisotropies. Our studies thus demonstrate that the mass splitting of $v_2$ and $v_3$ at low-$p_{perp}$ is not a unique signature of hydrodynamic collective flow but can be the interplay of several physics effects.
We propose an improved quark coalescence model for spin alignment of vector mesons by spin density matrix with phase space dependence. Within this model we propose an understanding of spin alignments of vector mesons $phi$ and $K^{*0}$ in the static limit: a large positive deviation of $rho_{00}$ for $phi$ mesons from $1/3$ may come from the electric part of the vector $phi$ field, while a negative deviation of $rho_{00}$ for $K^{*0}$ mesons may come from the electric part of vorticity fields. In the low-$p_T$ region, $rho_{00}$ for $K^{*0}$ mesons is proportional to $p_T^2$, which is qualitatively agree with experimental results.
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