David Seibert

“Intermittency” in high-energy and nuclear collisions

Abstract We calculate scaled factorial moments for ultra-relativistic collisions, using a cluster model that assumes only rough boost invariance of the cluster distribution and independent emission of pions from clusters. We find that the different moments are not independent, but are related by a simple scaling law. We show that the second moment contains the least statistical error, and is therefore the most useful for analyzing the behavior of the moments for small bin size. We also find that moments scale with the inverse of the rapidity density, if the cluster size is fixed. This scaling is not seen in the data; instead, the heavy-ion events contain larger clusters than are observed in the hadronic collisions. This disparity in cluster size indicates that spatial intermittency may be stronger in heavy-ion collisions than in the hadronic and light-ion collisions.

Moments of correlation functions in the small fluctuation limit

Abstract We propose a scaling law that relates all moments of a distribution to the second moment, in the limit of small fluctuations. The scaling law is derived for the scaled multiplicity moments, Ci, and the inclusive scaled factorial moments. The scaling law is independent of the source of the correlations, as it holds whenever quantities can be expanded about their mean values in a power series. Because of this scaling, the measurement of higher moments is not an efficient means of extracting additional information from data in the small fluctuation limit. We demonstrate that the multifractal moments obey a second scaling law. Moments that obey the second scaling law are dominated by single-particle effects and thus are not valid correlation functions.

New correlation functions for multi-particle processes

Abstract We propose a new family of correlation functions for the study of multi-particle processes, the “split-bin” correlation functions. Split-bin correlation functions are similar to scaled factorial moments, but they are less susceptible to some systematic errors, such as double-counting of particles. Unlike scaled factorial moments, split-bin correlation functions can be constructed using continuous variables, such as transverse energy. They can also be used to help differentiate between correlations due to jet-like and resonance-like sources.

High energy photons from quark-gluon plasma versus hot badronic gas

Abstract Photons in the energy range of about one-half to several GeV have been proposed as a signal of the formation of quark-gluon plasma in high energy collisions. To lowest order the thermal emission rate is infrared divergent for massless quarks, but we regulate this divergence using the resummation technique of Braaten and Pisarski. Photons can also be produced in the hadron phase. We find that the dominant contribution comes from the reactions ππ → ϱγ and πϱ → πγ ; the decays ω → πγ and ϱ → ππγ are also significant. Comparing the thermal emission rates at temperatures of order 150–200 MeV we conclude that the hadron gas shines just as brightly as quark-gluon plasma.

Hadron widths in mixed-phase matter

We derive classically an expression for a hadron width in a two-phase region of hadron gas and quark-gluon plasma (QGP). The presence of QGP gives hadrons larger widths than they would have in a pure hadron gas. We find that the [phi] width observed in a central Au+Au collision at [radical][ital s]=200 GeV/nucleon is a few MeV greater than the width in a pure hadron gas. The part of observed hadron widths due to QGP is approximately proportional to ([ital dN]/[ital dy])[sup [minus]1/3].

Correlation measurements in high-multiplicity events.

Requirements for correlation measurements in high-multiplicity events are discussed. Attention is focused on detection of so-called hot spots, two-particle rapidity correlations, two-particle momentum correlations (for quantum interferometry), and higher-order correlations. The signal-to-noise ratio may become large in the high-multiplicity limit, allowing meaningful single-event measurements, only if the correlations are due to collective behavior.