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Hybrid Hadronization is a new Monte Carlo package to hadronize systems of partons. It smoothly combines quark recombination applicable when distances between partons in phase space are small, and string fragmentation appropriate for dilute parton systems, following the picture outlined by Han et al. [PRC 93, 045207 (2016)]. Hybrid Hadronization integrates with PYTHIA 8 and can be applied to a variety of systems from $e^++e^-$ to $A+A$ collisions. It takes systems of partons and their color flow information, for example from a Monte Carlo parton shower generator, as input. In addition, if for $A+A$ collisions a thermal background medium is provided, the package allows sampling thermal partons that contribute to hadronization. Hybrid Hadronization is available for use as a standalone code and is also part of JETSCAPE since the 2.0 release. In these proceedings we review the physics concepts underlying Hybrid Hadronization and demonstrate how users can use the code with various parton shower Monte Carlos. We present calculations of hadron chemistry and fragmentation functions in small and large systems when Hybrid Hadronization is combined with parton shower Monte Carlos MATTER and LBT. In particular, we discuss observable effects of the recombination of shower partons with thermal partons.
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We study the data on mean hadron yields and contrast the chemical freezeout conditions in p+p, p+Pb and Pb+Pb at the Large Hadron Collider (LHC) energies. We study several schemes for freezeout that mainly differ in the way strangeness is treated: i. strangeness freezes out along with the non-strange hadrons in complete equilibrium (1CFO), ii. strangeness freezes out along with non-strange hadrons with an additional parameter $gamma_S$ accounting for non-equilibrium production of strangeness (1CFO+$gamma_S$), and iii. strangeness freezes out earlier than non-strange hadrons and in thermal equilibrium (2CFO). A comparison of the chisquares of the fits indicate a dependence of the freezeout scheme on the system size. The minimum bias p+p and different centralities of p+Pb and peripheral Pb+Pb data prefer 1CFO$+gamma_S$ with $gamma_S$ approaching unity as we go from p+p to central p+Pb and peripheral Pb+Pb. On the other hand, the mid-central to central Pb+Pb data prefer 2CFO over 1CFO+$gamma_S$. Such system size dependence of freezeout scheme could be an indication of the additional interaction in Pb+Pb over p+Pb and p+p.
Understanding the hadronization of the quark-gluon plasma (QGP) remains a challenging problem in the study of strong-interaction matter as produced in ultrarelativistic heavy-ion collisions (URHICs). The large mass of heavy quarks renders them excellent tracers of the color neutralization process of the QGP when they convert into various heavy-flavor (HF) hadrons. We develop a 4-momentum conserving recombination model for HF mesons and baryons that recovers the thermal and chemical equilibrium limits and accounts for space-momentum correlations (SMCs) of heavy quarks with partons of the hydrodynamically expanding QGP, thereby resolving a long-standing problem in quark coalescence models. The SMCs enhance the recombination of fast-moving heavy quarks with high-flow thermal quarks in the outer regions of the fireball. We also improve the hadro-chemistry with missing charm-baryon states, previously found to describe the large $Lambda_c/D^0$ ratio observed in proton-proton collisions. Both SMCs and hadro-chemistry, as part of our HF hydro-Langevin-recombination model for the strongly coupled QGP, importantly figure in the description of recent data for the $Lambda_c/D^0$ ratio and $D$-meson elliptic flow in URHICs.
Using QCD-inspired time dependent cross sections for pre-hadrons we provide a combined analysis of available experimental data on hadron attenuation in DIS off nuclei as measured by HERMES with 12 and 27 GeV and by EMC with 100 and 280 GeV lepton beam energies. We extract the complete four-dimensional evolution of the pre-hadrons using the JETSET-part of PYTHIA. We find a remarkable sensitivity of nuclear attenuation data to the details of the time-evolution of cross sections. Only cross sections evolving linearly in time describe the available data in a wide kinematical regime. Predictions for experimental conditions at JLAB (5 and 12 GeV beam energies) are included.
We compare the reconstructed hadronization conditions in relativistic nuclear collisions in the nucleon-nucleon centre-of-mass energy range 4.7-2760 GeV in terms of temperature and baryon-chemical potential with lattice QCD calculations, by using hadronic multiplicities. We obtain hadronization temperatures and baryon chemical potentials with a fit to measured multiplicities by correcting for the effect of post-hadronization rescattering. The post-hadronization modification factors are calculated by means of a coupled hydrodynamical-transport model simulation under the same conditions of approximate isothermal and isochemical decoupling as assumed in the statistical hadronization model fits to the data. The fit quality is considerably better than without rescattering corrections, as already found in previous work. The curvature of the obtained true hadronization pseudo-critical line kappa is found to be 0.0048 +- 0.0026, in agreement with lattice QCD estimates; the pseudo-critical temperature at vanishing mu_B is found to be 164.3+-1.8 MeV.
The hadronization of an expanding partonic fireball is studied within the Parton-Hadron-Strings Dynamics (PHSD) approach which is based on a dynamical quasiparticle model (DQPM) matched to reproduce lattice QCD results in thermodynamic equilibrium. Apart from strong parton interactions the expansion and development of collective flow is found to be driven by strong gradients in the parton mean-fields. An analysis of the elliptic flow $v_2$ demonstrates a linear correlation with the spatial eccentricity $epsilon$ as in case of ideal hydrodynamics. The hadronization occurs by quark-antiquark fusion or 3 quark/3 antiquark recombination which is described by covariant transition rates. Since the dynamical quarks become very massive, the formed resonant pre-hadronic color-dipole states ($qbar{q}$ or $qqq$) are of high invariant mass, too, and sequentially decay to the groundstate meson and baryon octets increasing the total entropy. This solves the entropy problem in hadronization in a natural way. Hadronic particle ratios turn out to be in line with those from a grandcanonical partition function at temperature $T approx 170$ MeV.
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