Fast Dynamical Evolution of Hadron Resonance Gas via Hagedorn States

Abstract

Abstract. Hagedorn states (HS) are a tool to model the hadronization process which occurs in the phase transition region between the quark gluon plasma (QGP) and the hadron resonance gas (HRG). These states are believed to appear near the Hagedorn temperature TH which in our understanding equals the critical temperature Tc. A covariantly formulated bootstrap equation is solved to generate the zoo of these particles characterized baryon number B, strangeness S and electric charge Q. These hadron-like resonances are characterized by being very massive and by not being limited to quantum numbers of known hadrons. All hadronic properties like masses, spectral functions etc. are taken from the hadronic transport model Ultra Relativistic Quantum Molecular Dynamics (UrQMD). Decay chains of single Hagedorn states provide a well description of experimentally observed multiplicity ratios of strange and multi-strange particles as the Ξ 0 -and the Ω − -baryon. In addition, the final energy spectra of resulting hadrons show a thermal-like distribution with the characteristic Hagedorn temperature TH . Box calculations including these Hagedorn states are performed. Indeed, the time scales leading to equilibration of the system are drastically reduced down to 2. . . 5 fm/c. IntroductionBack in the 60's of the last century and before the advent of quantum chromodynamics (QCD) as the theory of strong interactions, R. Hagedorn [1] proposed the existence of a whole zoo of massive, unobserved hadronic resonance states. The spectrum of these particles, known as Hagedorn spectrum, exhibits the specific feature of being exponential in the infinite mass limit with the slope given by the so called Hagedorn temperature T H . This temperature denotes the limiting temperature for hadronic matter since any partition function of a HRG with Hagedornlike mass spectrum diverges as long as T > T H . Above the Hagedorn temperature a new state of matter, namely the QGP, shall be realized. Thus, Hagedorn states provide a tool to understand the phase transition from HRG to QGP and back. The Hagedorn states are created in multi-particle collisions most abundantly near T H which in our understanding equals to the critical temperature T c . Hagedorn states are color neutral objects which are allowed to have any quantum numbers as long as they are compatible with its mass. The appearance of Hagedorn states in multi-particle collisions and their role was already discussed in [2,3,4,5,6]. Their appearance near T c can explain, as shown in [4,5,6], the fast chemical equilibration of (multi-) strange baryons B and their anti-particlesB at Relativistic Heavy Ion Collider (RHIC) energies. The inclusion of Hagedorn states in a hadron resonance gas model provides also a lowering of