Showing papers in "Annual Review of Nuclear and Particle Science in 1999"

Recent progress in baryogenesis

Abstract: ▪ Abstract We provide an up-to-date account of progress toward understanding the origin of the observed baryon asymmetry of the universe. We provide a pedagogical introduction to the primary areas of research in this field, giving a detailed description of the different scenarios. The very recent developments in Grand-Unified-Theory baryogenesis, leptogenesis, electroweak baryogenesis, and the Affleck-Dine mechanism are presented. In particular, we focus on specific particle physics implementations, mostly in the context of supersymmetry, which lead to specific testable predictions.

Two-particle correlations in relativistic heavy-ion collisions

Abstract: ▪ Abstract Two-particle momentum correlations between pairs of identical particles produced in relativistic heavy-ion reactions can be analyzed to extract the space-time structure of the collision fireball. We review recent progress in the application of this method, based on newly developed theoretical tools and new high-quality data from heavy-ion collision experiments. Implications for our understanding of the collision dynamics and for the search for the quark-gluon plasma are discussed.

Collective flow in heavy-ion collisions

Abstract: ▪ Abstract This chapter presents an experimental overview of collective flow phenomena in heavy-ion collisions in the incident energy regime from 100 AMeV to 160 AGeV. The characteristic features of various types of flow are described. The discussion of common dependences on the collision system and bombarding energy focuses on the different time scales of the underlying physics processes. Special emphasis is placed on the presence of structures in the excitation functions. The sensitivity of the available data to changes of nuclear-matter properties, e.g. equation of state, medium effects, and phase transitions, is discussed.

High-energy hadron-induced dilepton production from nucleons and nuclei

Abstract: ▪ Abstract We review the production of high-mass lepton pairs in fixed-target experiments, including both Drell-Yan (DY) and heavy quarkonium production [J/ψ, ψ′, ϒ(1S), ϒ(2S), and ϒ(3S)]. In recent years, DY data have become standard input to the determination of parton density distributions. DY data have recently yielded the first measurement of the x dependence of the , asymmetry of the proton. Similar to the observations in deeply inelastic scattering, precision measurements of the nuclear dependence of the proton-induced DY process exhibit shadowing at small target momentum fraction, x2. There is, however, no evidence of enhanced DY production from nuclear targets. Mean transverse momenta of DY pairs are observed to increase with target mass. These data, analyzed within a new theoretical framework, provide an estimation of the energy loss of fast quarks in nuclear matter. In contrast to the DY process, there are large nuclear effects in the production of all quarkonia. These effects show strong depen...

Charmonium suppression in heavy-ion collisions

Abstract: ▪ Abstract Data and their interpretations are reviewed for J/ψ and ψ′ production in heavy-ion collisions with particular emphasis on the recently reported anomaly in Pb-Pb reactions. The observed suppressions in pA collisions are discussed in terms of final-state absorption of a pre-meson and the pT distributions due to parton scattering in the initial state. The experimental setup is described and the various results for J/ψ and ψ′ suppressions, including their pT-dependence, are presented. The data, in particular the observed anomalous suppression in Pb-Pb collisions, are discussed in the light of the proposed ideas, among them quark-gluon plasma formation and suppression via co-movers.

Leptoquark searches at hera and the tevatron

Abstract: ▪ Abstract An unexpected excess of events with high Q2 reported by the H1 and ZEUS collaborations at HERA in early 1997 provoked speculation that the production of first-generation leptoquarks had been observed. In this article we review the anomalous HERA events, give a brief summary of the motivation for leptoquarks, and discuss the most recent searches at HERA and the Tevatron for first-, second-, and third-generation leptoquarks as well as generation-changing leptoquarks. We conclude with a short discussion of future prospects for leptoquark searches.

Inclusive jet and dijet production at the tevatron

Abstract: ▪ Abstract High-energy jet distributions measured since 1992 at the Fermilab Tevatron proton-antiproton collider are presented and compared with theoretical predictions. The statistical uncertainties on these measurements are significantly reduced relative to previous results. The systematic uncertainties are comparable in size to the uncertainty in the theoretical predictions. Although some discrepancies between theory and measurements are noted, the inclusive jet and dijet cross sections can be described by quantum chromodynamics. Prospects for reducing the uncertainty in the theoretical predictions by incorporating Tevatron measurements into the proton parton distributions are discussed. Dijet distributions, in excellent agreement with quantum chromodynamics, set a 2.5-TeV limit on the mass scale of quark constituents.