Event-by-Event Charge Fluctuations And Correlations From Hadron-Hadron To Relativistic Heavy Ion Collisions

Throughout human history, scientific theories and experiments of increasing power and sophistication have addressed these basic questions: what is the nature of the universe and what is it made of? The resulting knowledge has led to revolutionary insights into the nature of the world around us.Atoms were found to be divisible into nuclei and electrons. Nuclei in turn consist of nucleons, bound together by strong short-range forces. The basic theory of strong interaction, quantum chromodynamics (QCD), predicts all strongly interacting elementary particles (hadrons) are bound states of quarks or antiquarks. However, we have never observed free quarks directly until now. The current interpretation is that quarks cannot exist in a free state, basically because the attractive potential energy between quarks increases linearly with separation. This appears to be related to the fact that gluons, the intermediary particles for the strong force, can interact with each other as well as with quarks. It leads to a series of increasingly complex processes as quarks move farther and farther apart. The result is called quark confinement, individual quarks can never be observed outside of the confines of the observable particles which contain them.QCD predicts that at high temperature and (or) high energy density, hadronic matter will turn into a new state of matter, deconfined quark-gluon plasma (QGP). In laboratory, by colliding two high energy particle beams with each other, a large volumes of matter with high temperature and high energy density would be created. QGP might exist in such environments.The study on fluctuations is an essential method to characterize a physics system. With the advent of current high energy collisions there is the possibility to extract statistically significant dynamical information from individual collision events. The most efficient way to address fluctuations of a system is via the study of event-by-event fluctuations, where a given observable is measured on an event-by-event basis and the fluctuations are studied over the ensemble of the events. In most cases this analysis is equivalent to the measurement of two particle correlations, which in turn determine the response of the system to external perturbations. Event-by-...