Testing limits of statistical hadronization

نویسندگان

  • Johann Rafelski
  • Jean Letessier
چکیده

Much of the energy of the nuclei colliding at RHIC or SPS is converted into final state hadronic particles. About a quarter of this energy is in baryons and antibaryons. There are nearly 10 strange quark pairs per central rapidity participant. Do we really understand the hadronic particle yields? Do we need to introduce post-Fermi-model ideas such as chemical non-equilibrium in order to understand how a deconfined state hadronizes? 1. STATISTICAL HADRONIZATION Statistical Fermi-Pomeranchuk models have been used extensively to study particle yields and spectra since 1950 [1,2]. This approach was developed as a qualitative description of the gross features of particle production. It was originally not meant to be theoretically an accurate picture, just a phase space estimate of what Fermi called an upper limit on particle production in strong interaction processes. In fact, Fermi defined the limitations of the statistical approach stating three conditions: 1) exclusion of particles such as photons which have weak coupling to the interacting system; 2) absence of absolute chemical (abundance) equilibrium for many semi-weakly coupled particles; 3) requirement of relative baryochemical equilibrium. At that time strangeness was not yet discovered, and today we can add 3b) requirement of relative strangeness equilibrium. In the ensuing decade, another important feature of the strong interactions was discovered: the existence of numerous hadronic resonances. This property of hadronic interactions poses a challenge for the statistical hadronization model as the yield of particles is sensitive to the unidentified high mass hadron resonance states. We will discuss how this influences the expected particle yields in section 2. Our objective is to establish the magnitude of systematic theoretical error we have to expect given incomplete knowledge of the hadronic mass spectrum. A tacit assumption in our approach is that hadron-hadron interaction is well described by the formation of resonant states, and the remaining residual forces are negligible in comparison to the available energy content per particle. Understanding the hadro-chemistry, i.e., of the composition of particles produced, can fingerprint the phase of matter which has undergone statistical hadronization. Therefore, we will describe how chemical parameters, the chemical potentials µ i and the phase space

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تاریخ انتشار 2002