We present a new next-to-leading order calculation for fully dieren tial single-topquark nal states. The calculation is performed using phase space slicing and dipole subtraction methods. The results of the methods are found to be in agreement. The dipole subtraction method calculation retains the full spin dependence of the nal state particles. We show a few numerical results to illustrate the utility and consistency of the resulting computer implementations.

The fully differential single-top-quark cross section in next-to-leading order QCD

The rare decays $\stackrel{\ensuremath{\rightarrow}}{B}{K}^{(*)}{l}^{+}{l}^{\ensuremath{-}},$ $\stackrel{\ensuremath{\rightarrow}}{B}{K}^{(*)}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ and ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ are analyzed in a generic scenario where new physics effects enter predominantly via Z penguin contributions. We show that this possibility is well motivated on theoretical grounds, as the $\overline{s}\mathrm{bZ}$ vertex is particularly susceptible to nonstandard dynamics. In addition, such a framework is also interesting phenomenologically since the $\overline{s}\mathrm{bZ}$ coupling is rather poorly constrained by present data. The characteristic features of this scenario for the relevant decay rates and distributions are investigated. We emphasize that both sign and magnitude of the forward-backward asymmetry of the decay leptons in $\overline{B}\ensuremath{\rightarrow}{K}^{*}{l}^{+}{l}^{\ensuremath{-}},$ ${\mathcal{A}}_{\mathrm{FB}}^{(\overline{B})},$ carry sensitive information on new physics. The observable ${\mathcal{A}}_{\mathrm{FB}}^{(\overline{B})}+{\mathcal{A}}_{\mathrm{FB}}^{(B)}$ is proposed as a useful probe of nonstandard $\mathrm{CP}$ violation in $\overline{s}\mathrm{bZ}$ couplings.

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Phenomenology of nonstandard Z couplings in exclusive semileptonic b → s transitions

High energy photon colliders (γγ,γe) are based on e-e- linear colliders where high energy photons are produced using Compton scattering of laser light on high energy electrons just before the interaction point. This paper is a part of the Technical Design Report of the linear collider TESLA.1 Physics program, possible parameters and some technical aspects of the photon collider at TESLA are discussed.

/pdf/the-photon-collider-at-tesla-3evbjjygqg.pdf

The photon collider at TESLA

We present a calculation of the single top quark cross section for proton-antiproton interactions with {radical}(s)=1.8TeV at the Fermilab Tevatron collider. We examine the effects of the top quark mass, parton distribution functions, QCD scale, and collision energy, on each of the component production mechanisms, and study the kinematic distributions for standard model electroweak production. At the upgraded Tevatron with {radical}(s)=2.0TeV and high luminosity, it will be possible to test the nature of the Wtb coupling using single top quark production. We estimate the sensitivity to measure the single top quark cross section, and thus to directly measure V{sub tb} and the top quark partial width. We show what happens to the V{sub tb} measurement when an anomalous (V+A) component is added to the Wtb coupling, and how the top quark polarization affects the kinematic distributions. {copyright} {ital 1997} {ital The American Physical Society}

Single top quarks at the Fermilab Tevatron

We consider the Standard Model as an effective theory at the weak scale v of a generic new strong interaction that dynamically breaks electroweak symmetry at the energy scale Λ ~ (few) TeV. Assuming only the minimal field content with the Standard Model fermions and gauge bosons, but without a light Higgs particle, we construct the complete Lagrangian through next-to-leading order, that is, including terms of order v
 2
 /Λ2. The systematics behind this expansion is clarified. Although similar to chiral perturbation theory, it is not governed by the dimension of operators alone, but depends in an essential way on the loop expansion. Power-counting formulas are derived that indicate the classes of operators required at the next-to-leading order. The complete set of operators at leading and next-to-leading order is then listed, based on the restrictions implied by the Standard Model gauge symmetries. We recover the well-known operators discussed in the literature in connection with the electroweak chiral Lagrangian and in similar contexts, but we collect a complete and systematic list of all terms through order v
 2
 /Λ2. This includes some operators not discussed in explicit terms before. We also show that a few of the previously considered operators can be eliminated via the equations of motion. As another important result we confirm the known list of dimension-6 operators in the Standard Model with an elementary Higgs doublet, essentially as a special case of our scenario.

X. Zhang

Papers

Dynamical symmetry breaking and universality breakdown

Non-standard couplings of the top quark and precision measurements of the electroweak theory