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Register a new userCharmed hadron production in an improved quark coalescence model
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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.
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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.
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.
We develop for charmed hadron production in relativistic heavy-ion collisions a comprehensive coalescence model that includes an extensive set of $s$ and $p$-wave hadronic states as well as the strict energy-momentum conservation, which ensures the boost invariance of the coalescence probability and the thermal limit of the produced hadron spectrum. By combining our hadronization scheme with an advanced Langevin-hydrodynamics model that incorporates both elastic and inelastic energy loss of heavy quarks inside the dynamical quark-gluon plasma, we obtain a successful description of the $p_mathrm{T}$-integrated and differential $Lambda_c/D^0$ and $D_s/D^0$ ratios measured at RHIC and the LHC. We find that including the effect of radial flow of the medium is essential for describing the enhanced $Lambda_c/D^0$ ratio observed in relativistic heavy-ion collisions. We also find that the puzzling larger $Lambda_c/D^0$ ratio observed in Au+Au collisions at RHIC than in Pb+Pb collisions at the LHC is due to the interplay between the effects of the QGP radial flow and the charm quark transverse momentum spectrum at hadronization. Our study further suggests that charmed hadrons have larger sizes in medium than in vacuum.
The two-Equation of State (EoS) model is used to describe the hadron-quark phase transition in asymmetric matter formed at high density in heavy-ion collisions. For the quark phase, the three-flavor Nambu--Jona-Lasinio (NJL) effective theory is used to investigate the influence of dynamical quark mass effects on the phase transition. At variance to the MIT-Bag results, with fixed current quark masses, the main important effect of the chiral dynamics is the appearance of an End-Point for the coexistence zone. We show that a first order hadron-quark phase transition may take place in the region T=(50-80)MeV and rho_B=(2-4)rho_0, which is possible to be probed in the new planned facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna. From isospin properties of the mixed phase somepossible signals are suggested. The importance of chiral symmetry and dynamical quark mass on the hadron-quark phase transition is stressed. The difficulty of an exact location of Critical-End-Point comes from its appearance in a region of competition between chiral symmetry breaking and confinement, where our knowledge of effective QCD theories is still rather uncertain.
UrQMD phase-space coalescence calculations for the production of deuterons are compared with available data for various reactions from the GSI/FAIR energy regime up to LHC. It is found that the production process of deuterons, as reflected in their rapidity and transverse momentum distributions in p+p, p+A and A+A collisions at a beam energies starting from the GSI energy regime around 1 AGeV and up to the LHC, are in good agreement with experimental data. We further explore the energy and centrality dependence of the d/p ratios. Finally, we discuss anti-deuteron production for selected systems. Overall, a good description of the experimental data is observed. The results are also compatible with thermal model estimates. Most importantly this good description is based only on a single set of coalescence parameters that is independent of energy system size and can also be applied for anti-deuterons.
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