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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 book presents the latest results from high energy physics laboratories. The topics discussed include: Cosmology, Heavy Ions, Electroweak, Heavy Flavour Physics and CP Violation/Rare Decays, QCD and Beyond the Standard Model, Planck Scale Physics, Accelerator and Non-Accelerator Physics and Instrumentation.
This book deals with the most recent achievements in the following areas of high energy physics: physics of e+e- collisions, lepton-nucleon scattering, relativistic heavy ion collisions (the quest for quark-gluon plasma), and multiparticle production. New experimental results from Tevatron, LEP, SPS and HERA and the theoretical progress in the aforementioned fields are presented.
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 proceedings of the Joint International Lepton-Photon Symposium and Europhysics Conference on High Energy Physics cover the full range of frontline research in high energy particle physics. The latest results, both theoretical and experimental, are presented and reviews of recent developments in instrumentation and accelerator techniques are included.Volume one summarises the highly specialised topics presented in the parallel sessions while the second volume contains the review talks given by the invited speakers.
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.
This book contains review talks on many current topics in high energy particle physics and astroparticle physics, such as the status of precision tests of the Standard Model, tau and B physics at LEP, precision tests of QCD at LEP, WW physics and searches at LEP-2, heavy quark physics at the Tevatron collider, QCD studies at HERA, very high energy gamma astronomy, physics prospects at the LHC, physics prospects at linear colliders, and others. It also contains short status reports on several approved or planned experiments, namely DIRAC, HERA-B, AMS and ANTARES.