A Study Of Quark And Gluon Jets And Of The Long Distance Qcd Force Field At The Z

Quantum Chromodynamics (QCD) is widely accepted as the correct theory of the strong nuclear force in elementary particle physics. The precision to which QCD has been tested is relatively limited, however, compared to the precision to which other interactions such as the electro-weak one have been tested. In part, this is because the large value of the QCD coupling constant, [alpha]{sub s}, renders theoretical calculations based on perturbation theory relatively imprecise. The confinement of quarks and gluons inside hadrons also leads to uncertainty because the theoretical predictions cannot, in general, be tested directly against the experimental measurements but are subject to hadronization corrections. From an experimental standpoint, it has proven difficult to isolate gluon jets inside multi-jet events in an unbiased manner so as to determine gluon jet properties using model independent methods. Basic quark-gluon interactions such as the four-jet matrix element in ee− annihilations have been relatively untested due to the lack of a data sample with sufficient statistics. Perturbation theory has essentially nothing to say about the properties of the hadronization process itself. It is for these reasons that QCD has remained relatively untested.

Quantum Chromodynamics (QCD) is widely accepted as the correct theory of the strong nuclear force in elementary particle physics. The precision to which QCD has been tested is relatively limited, however, compared to the precision to which other interactions such as the electro-weak one have been tested. In part, this is because the large value of the QCD coupling constant, [alpha][sub s], renders theoretical calculations based on perturbation theory relatively imprecise. The confinement of quarks and gluons inside hadrons also leads to uncertainty because the theoretical predictions cannot, in general, be tested directly against the experimental measurements but are subject to hadronization corrections. From an experimental standpoint, it has proven difficult to isolate gluon jets inside multi-jet events in an unbiased manner so as to determine gluon jet properties using model independent methods. Basic quark-gluon interactions such as the four-jet matrix element in e[sup+]e[sup -] annihilations have been relatively untested due to the lack of a data sample with sufficient statistics. Perturbation theory has essentially nothing to say about the properties of the hadronization process itself. It is for these reasons that QCD has remained relatively untested.

The purpose of this volume is to trace the development of the theoretical understanding of quark-gluon plasma, both in terms of the equation of state and thermal correlation functions and in terms of its manifestation in high energy nuclear collisions. Who among us has not wondered how tall a mountain is on a neutron star, what happens when matter is heated and compressed to higher and higher densities, what happens when an object falls into a black hole, or what happened eons ago in the early universe? The study of quark-gluon plasma is related in one way or another to these and other thought provoking questions. Oftentimes the most eloquent exposition is given in the original papers. To this end a selection is made of what are the most important pioneering papers in this field. The early 1950s was an era when high energy multiparticle production in cosmic ray interactions attracted the attention of some of the brightest minds in physics, and so it should be no surprise that the first reprinted papers deal with the introduction of statistical models of particle production. The quark model arose in the 1960s, while QCD as such was recognized as the theory of the strong interactions in the 1970's. The behavior of matter at high temperatures and supranuclear densities became of wide interest in the nuclear and particle physics communities starting in the 1970s, which is when the concept of quark-gluon plasma became established. The history of the field has been traced up to the early 1990s. There are three reasons for stopping at that point in time. First, most of the key theoretical concepts and formalisms arose before 1993, although many of them continue to be developed today and hopefully well into the future. Second, papers written after 1992 are much more readily available than those writen before due to the advent of the World Wide Web and its electronic preprint databases and journals. Finally, in making this collection of reprints available as hardcopy one is limited in the number of pages, and some papers in the present selection should have been deleted in order to make room for post-1993 papers. For the same reason the subject focus must of necessity be limited, which means that in this reprint collection two wide subject areas are not addressed: the behavior of nuclear matter under extreme conditions is not reported, nor is quark matter in neutron stars. The broad categories into which the material has been placed, reflect the diverse studies of quark-gluon plasma and its manifestation. They are: phase-space models of particle production, perturbative QCD plasma, lattice gauge theory, fluid dynamics and flow, strangeness, heavy flavor (charm), electromagnetic signals, parton cascade and minijets, parton energy loss and jet quenching, Hanbury Brown--Twiss (HBT) interferometry, disoriented chiral condensates, phase transition dynamics and cosmology, and color superconductivity. Each chapter is prefaced by an introduction, which contains a list of significant papers which is more complete than the reprinted papers, though by no means exhaustive. It also contains citations to most relevant papers published up to the date of completion of this volume (fall 2002). It is hoped that the short reviews will help bring the reader up to date on the latest developments. The selection of papers cited in each chapter, and in particular the ones selected for reprinting, is solely the responsibility of the Editors. It is based on their best judgement and experience in this field dating back to the mid-1970s. In order to be reprinted a paper must have been pioneering in the sense of originality and impact on the field. Generally they have been cited over a hundred times by other papers published in refereed journals. The final selection was reviewed and discussed among the Editors repeatedly. Just because a paper is not included does not mean they do not know of it or do not have a high regard for it. All of the papers cited or reprinted are original research contributions. There are three other types of publications listed. The first is a compilation of books. The second is a list of reviews, many of which contain a significant amount of original material. The third is a list of the proceedings of the series of Quark Matter meetings, the primary series of international conferences in this field that is attended by both theorists and experimentalists.

This thesis contains new research in both experimental and theoretical particle physics, making important contributions in each. Two analyses of collision data from the ATLAS experiment at the LHC are presented, as well as two phenomenological studies of heavy coloured resonances that could be produced at the LHC. The first data analysis was the measurement of top quark-antiquark production with a veto on additional jet activity. As the first detector-corrected measurement of jet activity in top-antitop events it played an important role in constraining the theoretical modelling, and ultimately reduced these uncertainties for ATLAS's other top-quark measurements by a factor of two. The second data analysis was the measurement of Z+2jet production and the observation of the electroweak vector boson fusion (VBF) component. As the first observation of VBF at a hadron collider, this measurement demonstrated new techniques to reliably extract VBF processes and paved the way for future VBF Higgs measurements. The first phenomenological study developed a new technique for identifying the colour of heavy resonances produced in proton-proton collisions. As a by-product of this study an unexpected and previously unnoticed correlation was discovered between the probability of correctly identifying a high-energy top and the colour structure of the event it was produced in. The second phenomenological study explored this relationship in more detail, and could have important consequences for the identification of new particles that decay to top quarks.

The authors have studied differences between quark and gluon jets using 3-jet events in hadronic decays of Z° bosons collected by the SLD experiment at SLAC. Gluon jets were identified in symmetric 3-jet events containing one jet tagged as a heavy quark jet and compared with a mixed sample of quark and gluon jets and also with a mixed sample of light quark (u, d and s) and gluon jets. Their preliminary results show that the particle multiplicity in gluon jets is higher than that in light quark jets. These results are in qualitative agreement with QCD expectations. Differences are also observed in particle energy spectra and the jet widths, consistent with QCD expectations.

This is the fifth volume in the series on the subject of quark-gluon plasma, a unique phase created in heavy-ion collisions at high energy. It contains review articles by the world experts on various aspects of quark-gluon plasma taking into account the advances driven by the latest experimental data collected at both the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC). The articles are pedagogical and comprehensive which can be helpful for both new researchers entering the field as well as the experienced physicists working on the subject.

"This is the fifth volume in the series on the subject of quark-gluon plasma, a unique phase created in heavy-ion collisions at high energy. It contains review articles by the world experts on various aspects of quark-gluon plasma taking into account the advances driven by the latest experimental data collected at both the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC). The articles are pedagogical and comprehensive which can be helpful for both new researchers entering the field as well as the experienced physicists working on the subject."--

This thesis covers several important topics relevant to our understanding of quark-gluon plasma. It describes measurement of the third-order harmonic flow using two-particle correlations and isolation of flow and non-flow contributions to particle correlations in gold-gold collisions. The work also investigates long-range longitudinal correlations in small systems of deuteron-gold collisions. The former is related to the hydrodynamic transport properties of the quark-gluon plasma created in gold-gold collisions. The latter pertains to the question whether hydrodynamics is applicable to small systems, such as deuteron-gold collisions, and whether the quark-gluon plasma can be formed in those small-system collisions. The work presented in this thesis was conducted with the STAR experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, where the center-of-mass energy of both collision systems was a factor of 100 larger than the rest mass of the colliding nuclei. The results contained in this thesis are highly relevant to our quest for deeper understanding of quantum chromodynamics. The results obtained challenge the interpretation of previous works from several other experiments on small systems, and provoke a fresh look at the physics of hydrodynamics and particle correlations pertinent to high energy nuclear collisions.

This book reviews the latest experimental results on jet physics from proton-proton collisons at the LHC. Jets allow to determine the strong coupling constant over a wide range of energies up the highest ones possible so far, and to constrain the gluon parton distribution of the proton, both of which are important uncertainties on theory predictions in general and for the Higgs boson in particular.A novel approach in this book is to categorize the examined quantities according to the types of absolute, ratio, or shape measurements and to explain in detail the advantages and differences. Including numerous illustrations and tables the physics message and impact of each observable is clearly elaborated.

This is a review monograph on quark-gluon plasma (QGP). Different theoretical and experimental aspects of the program to produce QGP in relativistic heavy-ion collisions are covered by experts in the field. This is the third volume in a series on the subject, and the first such monograph to focus on the implications of the experimental results from RHIC, the relativistic heavy-ion collider at the National Brookhaven Laboratory. The review articles will be useful to experienced researchers as well as to graduate students entering the field.