Event-by-Event Fluctuations

Phase transitions are normally associated with large fluctuations. The QGP phase transition may yield non-statistical fluctuations in e.g. particle multiplicities, ratios and transverse momenta. These fluctuations might be detectable in final state observables, some of which can be studied on an event-by-event basis [16]. The requirement of high statistics per event for such analyses is met at RHIC and LHC energies, where a high multiplicity of particles is produced.

The idea of event-by-event, net charge fluctuations as a QGP signature is not directly related to the phase transition. The main issue is the distribution of electric charge in a QGP (where the quarks carry $\pm\htfrac13$ or $\pm\htfrac23$ unit charges), compared to the distribution in ordinary hadronic matter. It has been argued that the distribution of more evenly spread charge in a QGP would survive the phase transition back to hadronic matter [17,18]. This signature will be discussed in detail in chapter 3.