In a coalescence plus fragmentation approach we calculate the heavy baryon/meson ratio and the pT spectra of charmed hadrons D 0 , Ds and Λ + c in a wide range of transverse momentum from low pT up to about 10 GeV and discuss their ratios from RHIC to LHC energies without any change of the coalescence parameters. We have included the contribution from decays of heavy hadron resonances and also the one due to fragmentation of heavy quarks which do not undergo the coalescence process. The coalescence process is tuned to have all charm quarks hadronizing in the pT → 0 limit and at finite pT charm quarks not undergoing coalescence are hadronized by independent fragmentation. The pT dependence of the baryon/meson ratios are found to be sensitive to the masses of coalescing quarks, in particular the Λc/D 0 can reach values of about 1 ÷ 1.5 at pT ≈ 3 GeV, or larger, similarly to the light baryon/meson ratio like p/π and Λ/K, however a marked difference is a quite weak pT dependence with respect to the light case, such that a larger value at intermediate pT implies a relatively large value also for the integrated yields. A comparison with other coalescence model and with the prediction of thermal model is discussed.
We present the novel microscopic n-body dynamical transport approach PHQMD (Parton-Hadron-Quantum-Molecular-Dynamics) for the description of particle production and cluster formation in heavy-ion reactions at relativistic energies. The PHQMD extends the established PHSD (Parton-Hadron-String-Dynamics) transport approach by replacing the mean-field by density dependent two body interactions in a similar way as in the Quantum Molecular Dynamics (QMD) models. This allows for the calculation of the time evolution of the n-body Wigner density and therefore for a dynamical description of cluster and hypernuclei formation. The clusters are identified with the MST (Minimum Spanning Tree) or the SACA (Simulated Annealing Cluster Algorithm) algorithm which -by regrouping the nucleons in single nucleons and noninteracting clusters -generates the most bound configuration of nucleons and clusters. Collisions among particles in PHQMD are treated in the same way as in PHSD. The PHQMD approach can be used in different modes for the hadron propagation: the mean-field based PHSD mode and the QMD mode based on different density dependent two-body potentials between the nucleons which correspond to the different equationsof-state (EoS). This allows to study the sensitivity of observables on the different descriptions of the potential interactions among nucleons. Here we present the first PHQMD results for general 'bulk' observables such as rapidity distributions and transverse mass spectra for hadrons (π, K,K, p,p, Λ,Λ) from SIS to RHIC energies, as well as for cluster production, including hypernuclei.
Several transport models have been employed in recent years to analyze heavy-flavor meson spectra in high-energy heavy-ion collisions. Heavy-quark transport coefficients extracted from these models with their default parameters vary, however, by up to a factor of 5 at high momenta. To investigate the origin of this large theoretical uncertainty, a systematic comparison of heavy-quark transport coefficients is carried out between various transport models. Within a common scheme devised for the nuclear modification factor of charm quarks in a brick medium of a quark-gluon plasma, the systematic uncertainty of the extracted drag coefficient among these models is shown to be reduced to a factor of 2, which can be viewed as the smallest intrinsic systematical error band achievable at present time. This indicates the importance of a realistic hydrodynamic evolution constrained by bulk hadron spectra and of heavy-quark hadronization for understanding the final heavy-flavor hadron spectra and extracting heavy-quark drag coefficient. The transverse transport coefficient is less constrained due to the influence of the underlying mechanism for heavy-quark medium interaction. Additional constraints on transport models such as energy loss fluctuation and transverse-momentum broadening can further reduce theoretical uncertainties in the extracted transport coefficients.
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