Stephen J. Parke

Top quark production: Sensitivity to new physics.

The production cross–section and distributions of the top quark are sensitive to new physics, e.g., the tt system can be a probe of new resonances or gauge bosons that are strongly coupled to the top quark, in analogy to Drell–Yan production. The existence of such new physics is expected in dynamical electroweak symmetry breaking schemes, and associated with the large mass of the top quark. The total top production cross–section can be more than doubled, and distributions significantly distorted with a chosen scale of new physics of ∼ 1 TeV in the vector color singlet or octet s–channel. New resonance physics is most readily discernible in the high–pT distributions of the single top quark and of the W boson.

Perturbative QCD utilizing extended supersymmetry

We use N = 2 extended supersymmetry to dramatically simplify the diagrammatic calculations of perturbative QCD. The production, by gluon-gluon fusion, of two gluons, three gluons, and two massless gluinos plus a gluon are used as examples.

Angular correlations in top quark pair production and decay at hadron colliders

We show how to observe sizable angular correlations between the decay products of the top quark and those of the top antiquark in top quark pair production and decay at hadron colliders. These correlations result from the large asymmetry in the rate for producing like-spin versus unlike-spin top quark pairs provided the appropriate spin axes are used. The effects of new physics at production or decay on these correlations are briefly discussed. {copyright} {ital 1996 The American Physical Society.}

CP violation and neutrino oscillations

Abstract We review the basic mechanisms of neutrino mass generation and the corresponding structure of the lepton mixing matrix. We summarize the status of three-neutrino oscillation parameters as determined from current observations, using state-of-the-art solar and atmospheric neutrino fluxes, as well as latest experimental data as of September 2007. We also comment on recent attempts to account for these results and to understand flavour from first principles. We discuss extensively the prospects of probing the strength of CP violation in two near term accelerator neutrino oscillation experiments, T2K and NO ν A , as well as possible extensions such as T2KK and a second large off-axis detector near the NO ν A detector. We also briefly discuss the possibility of probing the effect of Majorana phases in future neutrinoless double beta decay searches and discuss other implications of leptonic CP violation such as leptogenesis. Finally we comment on the issue of robustness of the current oscillation interpretation and possible ways of probing for non-standard neutrino interactions in precision oscillation studies.

Another possible way to determine the neutrino mass hierarchy

We show that by combining high precision measurements of the atmospheric

Maximizing spin correlations in top quark pair production at the Tevatron

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Improved spin basis for angular correlation studies in single top quark production at the Fermilab Tevatron

in both the electron and muon neutrino (or antineutrino) disappearance channels one can determine the neutrino mass hierarchy. The required precision is a very challenging fraction of one per cent for both measurements. At even higher precision, sensitivity to the cosine of the

Spin correlations in top-quark pair production at e+e− colliders

CP

Spin correlation effects in top quark pair production at the LHC

violating phase is also possible. This method for determining the mass hierarchy of the neutrino sector does not depend on matter effects.

Parameter degeneracies in neutrino oscillation measurement of leptonic CP and T violation

Abstract A comparison is made between the off-diagonal and helicity spin bases for top quark pair production at the FNAL Tevatron. In the off-diagonal basis, 92% of the top quark pairs are in the spin configuration up-down plus down-up, whereas in the helicity basis only 70% are left-right plus right-left. The off-diagonal basis maximizes the spin asymmetry and hence the measured angular correlations between the decay products, which are more than twice as big in this basis as compared to the helicity basis. In addition, for the process q q → tt , we give a very simple analytic expression for the matrix element squared which includes all spin correlations between the production and subsequent decay of the top quarks.