Properties of hadronic matter near the phase transition

Eigenschaften der hadronischen Materie nahe des Phasenübergangs

  • In order to fully understand the new state of matter formed in heavy ion collisions, it is vital to isolate the always present final state hadronic contributions within the primary Quark-Gluon Plasma (QGP) experimental signatures. Previously, the hadronic contributions were determined using the properties of the known mesons and baryons. However, according to Hagedorn, hadrons should follow an exponential mass spectrum, which the known hadrons follow only up to masses of M = 2 GeV. Beyond this point the mass spectrum is flat, which indicates that there are "missing" hadrons, that could potentially contribute significantly to experimental observables. In this thesis I investigate the influence of these "missing" Hagedorn states on various experimental signatures of QGP. Strangeness enhancement is considered a signal for QGP because hadronic interactions (even including multi-mesonic reactions) underpredict the hadronic yields (especially for strange particles) at the Relativistic Heavy Ion Collider, RHIC. One can conclude that the time scales to produce the required amount of hadronic yields are too long to allow for the hadrons to reach chemical equilibrium within the lifetime of a cooling hadronic fireball. Because gluon fusion can quickly produce strange quarks, it has been suggested that the hadrons are born into chemical equilibrium following the Quantum Chromodynamics (QCD) phase transition. However, we show here that the missing Hagedorn states provide extra degrees of freedom that can contribute to fast chemical equilibration times for a hadron gas. We develop a dynamical scheme in which possible Hagedorn states contribute to fast chemical equilibration times of X X pairs (where X = p, K, Lambda, or Omega) inside a hadron gas and just below the critical temperature. Within this scheme, we use master equations and derive various analytical estimates for the chemical equilibration times. Applying a Bjorken picture to the expanding fireball, the hadrons can, indeed, quickly chemically equilibrate for both an initial overpopulation or underpopulation of Hagedorn resonances. We compare the thermodynamic properties of our model to recent lattice results and find that for both critical temperatures, Tc = 176 MeV and Tc = 196 MeV, the hadrons can reach chemical equilibrium on very short time scales. Furthermore the ratios p/pi, K/pi , Lambda/pi, and Omega/pi match experimental values well in our dynamical scenario. The effects of the "missing" Hagedorn states are not limited to the chemical equilibration time. Many believe that the new state of matter formed at RHIC is the closet to a perfect fluid found in nature, which implies that it has a small shear viscosity to entropy density ratio close to the bound derived using the uncertainty principle. Our hadron resonance gas model, including the additional Hagedorn states, is used to obtain an upper bound on the shear viscosity to entropy density ratio, eta/s, of hadronic matter near Tc that is close to 1/(4pi). Furthermore, the large trace anomaly and the small speed of sound near Tc computed within this model agree well with recent lattice calculations. We also comment on the behavior of the bulk viscosity to entropy density ratio of hadronic matter close to the phase transition, which qualitatively has a different behavior close to Tc than a hadron gas model with only the known resonances. We show how the measured particle ratios can be used to provide non-trivial information about Tc of the QCD phase transition. This is obtained by including the effects of highly massive Hagedorn resonances on statistical models, which are generally used to describe hadronic yields. The inclusion of the "missing" Hagedorn states creates a dependence of the thermal fits on the Hagedorn temperature, TH , and leads to a slight overall improvement of thermal fits. We find that for Au+Au collisions at RHIC at sqrt{sN N} = 200 GeV the best square fit measure, chi^2 , occurs at TH = Tc = 176 MeV and produces a chemical freeze-out temperature of 172.6 MeV and a baryon chemical potential of 39.7 MeV.
  • Die vorliegende Arbeit greift das bekannte Konzept von Hagedornzuständen auf, um damit neue physikalische Effekte in hadronischer Materie nahe der kritischen Temperatur $T_c$ (Die kritische Temperatur bestimmt den Phasenübergang von der hadronischen Materie zum Quark-Gluon Plasma.) in einem Beschleunigerring für relativistische Schwerionen zu untersuchen. Dieses Konzept wurde in den 1960er Jahren von Rolf Hagedorn eingeführt und beruht darauf, dass hadronische Resonanzen einem exponentiellen Spektrum folgen. Seit den Arbeiten von Hagedorn wurden viele neue Resonanzen gefunden, jedoch weisen sie bis zu einer Masse von $M=2$ GeV weiterhin ein exponentielles Spektrum auf. Für größere Massen flacht das Spektrum allerdings ab, was darauf hinweist, dass bislang noch nicht alle Resonanzen bekannt sind. In dieser Arbeit wird die Existenz solcher Resonanzen angenommen und ihre Auswirkungen auf verschiedene Signaturen des Quark-Gluon Plasmas untersucht. ...

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Author:Jacquelyn Noronha-HostlerORCiDGND
Referee:Carsten GreinerGND
Document Type:Doctoral Thesis
Date of Publication (online):2010/12/15
Year of first Publication:2010
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Granting Institution:Johann Wolfgang Goethe-Universität
Date of final exam:2010/12/08
Release Date:2010/12/15
Tag:Hagedorn Zustände; Ratengleichungen
Collective Flow; Hagedorn states; Heavy-ion Collisions; Master Equations; Strangeness Enhancement
GND Keyword:Hadron; Quark-Gluon-Plasma; Strangeness; STAR <Teilchendetektor>; LHC; PHENIX <Teilchendetektor>
Institutes:Physik / Physik
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik
Licence (German):License LogoDeutsches Urheberrecht