Quick chemical equilibration times of hadrons (specifically, pp , KK , ΛΛ, and ΩΩ pairs) within a hadron gas are explained dynamically using Hagedorn states, which drive particles into equilibrium close to the critical temperature. Within this scheme, we use master equations and derive various analytical estimates for the chemical equilibration times. We compare our model to recent lattice results and find that for both Tc = 176 MeV and Tc = 196 MeV, the hadrons can reach chemical equilibrium almost immediately, well before the chemical freeze-out temperatures found in thermal fits for a hadron gas without Hagedorn states. Furthermore the ratios p/π, K/π , Λ/π, and Ω/π match experimental values well in our dynamical scenario.
Hagedorn states are characterized by being very massive hadron-like resonances and by not being limited to quantum numbers of known hadrons. To generate such a zoo of different Hagedorn states, a covariantly formulated bootstrap equation is solved by ensuring energy conservation and conservation of baryon number B, strangeness S, and electric charge Q. The numerical solution of this equation provides Hagedorn spectra, which also enable us to obtain the decay width for Hagedorn states needed in cascading decay simulations. A single Hagedorn state cascades by various two-body decay channels subsequently into final stable hadrons. All final hadronic observables such as masses, spectral functions, and decay branching ratios for hadronic feed-down are taken from a hadronic transport model. Strikingly, the final energy spectra of resulting hadrons are exponential, showing a thermal-like distribution with the characteristic Hagedorn temperature.
Hagedorn states are the key to understand how all hadrons observed in high energy heavy ion collisions seem to reach thermal equilibrium so quickly. An assembly of Hagedorn states is formed in elementary hadronic or heavy ion collisions at hadronization. Microscopic simulations within the transport model UrQMD allow to study the time evolution of such a pure non-equilibrated Hagedorn state gas towards a thermally equilibrated Hadron Resonance Gas by using dynamics, which unlike strings, fully respect detailed balance. Propagation, repopulation, rescatterings and decays of Hagedorn states provide the yields of all hadrons up to a mass of m = 2.5 GeV. Ratios of feed down corrected hadron multiplicities are compared to corresponding experimental data from the ALICE collaboration at LHC. The quick thermalization within t = 1 − 2 fm/c of the emerging Hadron Resonance Gas exposes Hagedorn states as a tool to understand hadronization.
The early stage of high multiplicity pp, pA and AA collider is represented by a nearly quarkless, hot, deconfined pure gluon plasma. According to pure Yang -Mills Lattice Gauge Theory, this hot pure glue matter undergoes, at a high temperature, Tc = 270 MeV, a first order phase transition into a confined Hagedorn-GlueBall fluid. These new scenario should be characterized by a suppression of high pT photons and dileptons, baryon suppression and enhanced strange meson production. We propose to observe this newly predicted class of events at LHC and RHIC. 12.38.Mh, 24.85.+p The proper understanding of the initial and the early stage of ultra-relativistic pp-, pA-and heavy ion AAcollisions is a topic of great importance for our understanding of hot and dense QCD matter formed in the laboratory and its phase structure.At present, the community favors a paradigm of an extremely rapid (t eq less than 0.3 fm/c) thermalization and chemical saturation of soft gluons and light quarks, their masses and momenta emerging from the decay of coherent massive color flux tubes of strings, which are formed in the primary hadron-hadron collisions.However, for a long time also another scenario has been discussed, namely the hot glue scenario, where the initial stage is dominated by gluons [5,57,68,105].We ask the question whether due to initial state color coherence fluctuations two quite distinct classes of events may exist in collider experiments, or in ultra high energy cosmic ray events, UHECR events. They could be experimentally distinguished in a high statistics analysis of the collider data at RHIC, LHC, and the FCC, from UHE-CRs, or from high intensity fixed target experiments at FAIR [2-4, 29, 38-40, 42, 43, 47, 48, 50, 58, 61, 62, 64, 89-99], NICA [56] and J-Parc.Do soft particles at midrapidity in pp-, pA-, and AAcollider experiments develop from an initially quark-free color glass condensate, CGC, through a pre-equilibrium Glasma-stage into a rapidly chemically saturated, thermalized quarkless pure gluon plasma [110] (see Fig. 1(a)) [36]?The CGC model predicts that the early Glasma is strongly overpopulated -that means that a 'simple' thermally equilibrated Bose-Einstein distribution can NOT exist, as it can not accommodate the overabundant gluons.Hence, dynamically a temporary gluon condensate [19,111] may be formed in order to accomodate those excess gluons, at least transiently, see for example Fig. 1(b).The surprising finding is that only very few soft quarks are present in this early stage according to modern transport calculations [9,10,18,35,84,107] (see, however, also [85,86], where opposite conclusion of quark equilibration is drawn, mostly due to that they put massive gluons there which can easier produce the lighter quarks, while considering Debye screening and other non-perturbative arXiv:1509.00160v1 [hep-ph] 1 Sep 2015
Background: Statistical models are successfully used to describe particle multiplicities in (ultra-)relativistic heavy ion collisions. Transport models usually lack to describe special aspects of the results of these experiments, as the fast equilibration and some multiplicity ratios.Purpose: A novel, unorthodox picture of the dynamics of heavy ion collisions is developed using the concept of Hagedorn states.Method: A prescription of the bootstrap of Hagedorn states respecting the conserved quantum numbers baryon number B, strangeness S, isospin I is implememted into the GiBUU transport model. Results: Using a strangeness saturation suppression factor suitable for nucleon-nucleon-collisions, recent experimental data for the strangeness production by the HADES collaboration in Au+Au and Ar+KCl is reasonable well described. The experimental observed exponential slopes of the energy distributions are nicely reproduced.Conclusions: A dynamical model using Hagedorn resonance states, supplemented by a strangeness saturation suppression factor, is able to explain essential features (multiplicities, exponential slope) of experimental data for strangeness production in nucleus-nucleus collisions close to threshold.
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