Search Results (4 total)

Anomalous quartic couplings between the electroweak gauge bosons may contribute to the νν̅ γγ and qq̅ γγ final states produced in e⁺e^- collisions. This analysis uses the LEP2 OPAL data sample at center-of-mass energies up to 209 GeV. Event selections identify νν̅ γγ and qq̅ γγ events in which the two photons are reconstructed within the detector acceptance. The cross section for the process e⁺e^-→qq̅ γγ is measured. Averaging over all energies, the ratio of the observed e⁺e^-→qq̅ γγ cross section to the standard model expectation is R(data/SM)=0.92±0.07±0.04, where the errors represent the statistical and systematic uncertainties respectively. The νν̅ γγ and qq̅ γγ data are used to constrain possible anomalous W⁺W^-γγ and ZZγγ couplings. Combining with previous OPAL results from the W⁺W^-γ final state, the 95% confidence level limits on the anomalous coupling parameters a₀^Z, a_c^Z, a₀^W and a_c^W are found to be -0.007 GeV^-2<a₀^Z/Λ²<0.023 GeV^-2, -0.029 GeV^-2<a_c^Z/Λ²<0.029 GeV^-2, -0.020 GeV^-2<a₀^W/Λ²<0.020 GeV^-2, -0.052 GeV^-2<a_c^W/Λ²<0.037 GeV^-2, where Λ is the energy scale of the new physics. Limits found when allowing two or more parameters to vary are also presented.

We present the first experimental results based on the jet boost algorithm, a technique to select unbiased samples of gluon jets in e⁺e^- annihilations, i.e. gluon jets free of biases introduced by event selection or jet finding criteria. Our results are derived from hadronic Z⁰ decays observed with the OPAL detector at the LEP e⁺e^- collider at CERN. First, we test the boost algorithm through studies with HERWIG Monte Carlo events and find that it provides accurate measurements of the charged particle multiplicity distributions of unbiased gluon jets for jet energies larger than about 5 GeV, and of the jet particle energy spectra (fragmentation functions) for jet energies larger than about 14 GeV. Second, we apply the boost algorithm to our data to derive unbiased measurements of the gluon jet multiplicity distribution for energies between about 5 and 18 GeV, and of the gluon jet fragmentation function at 14 and 18 GeV. In conjunction with our earlier results at 40 GeV, we then test QCD calculations for the energy evolution of the distributions, specifically the mean and first two nontrivial normalized factorial moments of the multiplicity distribution, and the fragmentation function. The theoretical results are found to be in global agreement with the data, although the factorial moments are not well described for jet energies below about 14 GeV.

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact high-energy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.

The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides work on the parameters of a 3–4 and 0.5 TeV center-of-mass (COM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (COM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay (π→μν_μ) channel, muon cooling, acceleration, storage in a collider ring, and the collider detector. We also present theoretical and experimental R&D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the research and development since the feasibility study of muon colliders presented at the Snowmass '96 Workshop [R. B. Palmer, A. Sessler, and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].