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M. Roth

Publications and source records attributed to M. Roth.

227 records · Page 13Linked to original sources

Four-Fermion Production in Electron-Positron Collisions

This report summarises the results of the four-fermion working group of the LEP2-MC workshop, held at CERN from 1999 to 2000. Recent developments in the calculation of four-fermion processes in electron-positron collisions at LEP-2 centre-of-mass energies are presented, concentrating on predictions for four main reactions: W-pair production, visible photons in four-fermion events, single-W production and Z-pair production. Based on a comparison of results derived within different approaches, theoretical uncertainties on these predictions are established.

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Precise predictions for W-pair production at LEP2 with RACOONWW

RACOONWW is the first Monte Carlo generator for e+e- --> WW --> 4f(+gamma) that includes the electroweak O(alpha) radiative corrections in the double-pole approximation completely. Some numerical results for LEP2 energies are discussed, and the predictions for the total W-pair cross section are confronted with LEP2 data.

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W-pair production at future e+e- colliders: precise predictions from RACOONWW

We present numerical results for total cross sections and various distributions for e+e- --> WW --> 4f(+gamma) at a future 500GeV linear collider, obtained from the Monte Carlo generator RACOONWW. This generator is the first one that includes O(alpha) electroweak radiative corrections in the double-pole approximation completely. Owing to their large size the corrections are of great phenomenological importance.

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Four-fermion production with RACOONWW

RACOONWW is an event generator for e+e- --> WW --> 4fermions(+gamma) that includes full tree-level predictions for e+e- --> 4f and e+e- --> 4f+gamma as well as O(alpha) corrections to e+e- --> 4f in the so-called double-pole approximation. We briefly sketch the concept of the calculation on which this generator is based and present some numerical results.

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O(alpha) corrections to e+e- --> WW --> 4fermions(+gamma): first numerical results from RACOONWW

First numerical results of the Monte Carlo generator RACOONWW for e+e- --> WW --> 4fermions(+gamma) in the electroweak Standard Model are presented. This event generator is the first one that includes O(alpha) electroweak radiative corrections in the double-pole approximation completely. We briefly describe the strategy of the calculation and give numerical results for total cross sections, including CC03, and various distributions.

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Near-infrared photometry of isolated spirals with and without an AGN. I: The Data

We present infrared imaging data in the J and K' bands obtained for 18 active spiral galaxies, together with 11 non active galaxies taken as a control sample. All of them were chosen to satisfy well defined isolation criteria so that the observed properties are not related to gravitational interaction. For each object we give: the image in the K' band, the sharp-divided image (obtained by dividing the observed image by a filtered one), the difference image (obtained by subtracting a model to the observed one), the color J-K' image, the ellipticity and position angle profiles, the surface brightness profiles in J and K', their fits by bulge+disk models and the color gradient. We have found that four (one) active (control) galaxies previously classified as non-barred turn out to have bars when observed in the near-infrared. One of these four galaxies (UGC 1395) also harbours a secondary bar. For 15 (9 active, 6 control) out of 24 (14 active, 10 control) of the optically classified barred galaxies (SB or SX) we find that a secondary bar (or a disk, a lense or an elongated ring) is present. The work presented here is part of a large program (DEGAS) aimed at finding whether there are differences between active and non active galaxies in the properties of their central regions that could be connected with the onset of nuclear activity.

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Radiative corrections to e^+e^- -> WW -> 4 fermions

The structure of the double-pole approximation for the O(alpha) corrections to e^+e^- -> WW -> 4 fermions is described, and some results are presented. Moreover, results on full tree-level predictions for $e^+e^- -> WW -> 4 fermions + gamma are given.

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Predictions for all processes e^+e^- -> 4 fermions + gamma

The complete matrix elements for e^+ e^- -> 4f and e^+ e^- -> 4f + gamma are calculated in the Electroweak Standard Model for polarized massless fermions. The matrix elements for all final states are reduced to a few compact generic functions. Monte Carlo generators for e^+ e^- -> 4f and e^+ e^- -> 4f + gamma are constructed. We compare different treatments of the finite widths of the electroweak gauge bosons; in particular, we include a scheme with a complex gauge-boson mass that obeys all Ward identities. The detailed discussion of numerical results comprises integrated cross sections as well as photon-energy distributions for all different final states.

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Further numerical results on non-factorizable corrections to e+e- --> 4fermions

Numerical results on non-factorizable corrections to e+e- --> WW --> 4fermions with semi-leptonic and hadronic final states, as well as to e+e- --> ZZ --> 4fermions, are presented. The corrections turn out to be small in comparison to the experimental uncertainty of LEP2, but they might compete with the expected accuracy at future e+e--colliders.

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Non-factorizable photonic corrections to ee->WW->4fermions

We study the non-factorizable corrections to W-pair-mediated four-fermion production in ee annihilation in double-pole approximation. We show how these corrections can be combined with the known corrections to the production and the decay of on-shell W-boson pairs, and how the full off-shell Coulomb singularity is included. Moreover, we find that the actual form of the real non-factorizable corrections depends on the parametrization of phase space, more precisely, on the definition of the invariant masses of the resonant W bosons. For the usual parametrization the full analytical results for the non-factorizable corrections are presented. Our analytical and numerical results for the non-factorizable corrections agree with a recent calculation, which was found to differ from a previous one. The detailed numerical discussion covers the invariant-mass distribution, various angular distributions, and the lepton-energy distribution for leptonic final states.

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High-Energy Approximation of One-Loop Feynman Integrals

We provide high-energy approximations for all one-loop scalar 3- and 4-point functions and the corresponding tensor integrals that appear in scattering processes with four external on-shell particles. Our expressions are valid if all kinematical invariants are much larger than the internal and external masses. They contain all leading-order terms of the integrals.

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