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A. Werthenbach

Publications and source records attributed to A. Werthenbach.

14 recordsLinked to original sources
arXiv2004

Physics at the CLIC Multi-TeV Linear Collider

This report summarizes a study of the physics potential of the CLIC e+e- linear collider operating at centre-of-mass energies from 1 TeV to 5 TeV with luminosity of the order of 10^35 cm^-2 s^-1. First, the CLIC collider complex is surveyed, with emphasis on aspects related to its physics capabilities, particularly the luminosity and energy, and also possible polarization, γγand e-e- collisions. The next CLIC Test facility, CTF3, and its R&D programme are also reviewed. We then discuss aspects of experimentation at CLIC, including backgrounds and experimental conditions, and present a conceptual detector design used in the physics analyses, most of which use the nominal CLIC centre-of-mass energy of 3 TeV. CLIC contributions to Higgs physics could include completing the profile of a light Higgs boson by measuring rare decays and reconstructing the Higgs potential, or discovering one or more heavy Higgs bosons, or probing CP violation in the Higgs sector. Turning to physics beyond the Standard Model, CLIC might be able to complete the supersymmetric spectrum and make more precise measurements of sparticles detected previously at the LHC or a lower-energy linear e+e- collider: γγcollisions and polarization would be particularly useful for these tasks. CLIC would also have unique capabilities for probing other possible extensions of the Standard Model, such as theories with extra dimensions or new vector resonances, new contact interactions and models with strong WW scattering at high energies. In all the scenarios we have studied, CLIC would provide significant fundamental physics information beyond that available from the LHC and a lower-energy linear e+e- collider, as a result of its unique combination of high energy and experimental precision.

hep-ph↗
arXiv2003

Elektroweak one-loop corrections for e^+e^- annihilation into t\bar{t} including hard bremsstrahlung

We present the complete electroweak one-loop corrections to top-pair production at a linear e^+e^- collider in the continuum region. Besides weak and photonic virtual corrections, real hard bremsstrahlung with simple realistic kinematical cuts is included. For the bremsstrahlung we advocate a semi-analytical approach with a high numerical accuracy. The virtual corrections are parametrized through six independent form factors, suitable for Monte-Carlo implementation. Alternatively, our numerical package topfit, a stand-alone code, can be utilized for the calculation of both differential and integrated cross sections as well as forward--backward asymmetries.

hep-ph↗
arXiv2002

Status of Electroweak Corrections to Top Pair Production

We review the status of electroweak radiative corrections to top-pair production at a Linear Collider well above the production threshold. We describe the Fortran package topfit and present numerical results at sqrt(s) = 500 GeV, 1 TeV, and 3 TeV.

hep-ph↗
arXiv2002

Massive two-loop Bhabha scattering -- the factorizable subset

The experimental precision that will be reached at the next generation of colliders makes it indispensable to improve theoretical predictions significantly. Bhabha scattering (e^+ e^- \to e^+ e^-) is one of the prime processes calling for a better theoretical precision, in particular for non-zero electron masses. We present a first subset of the full two-loop calculation, namely the factorizable subset. Our calculation is based on DIANA. We reduce tensor integrals to scalar integrals in shifted (increased) dimensions and additional powers of various propagators, so-called dots-on-lines. Recurrence relations remove those dots-on-lines as well as genuine dots-on-lines (originating from mass renormalization) and reduce the dimension of the integrals to the generic d = 4 - 2 εdimensions. The resulting master integrals have to be expanded to ${\it O}(ε)$ to ensure proper treatment of all finite terms.

hep-ph↗
arXiv2002

Factorizing one-loop contributions to two-loop Bhabha scattering and automatization of Feynman diagram calculations

In higher order calculations a number of new technical problems arise: one needs diagrams in arbitrary dimension in order to obtain their needed $ε$-expansion, zero Gram determinants appear, renormalization produces diagrams with `dots' on the lines, i.e. higher order powers of scalar propagators. All these problems cannot be accessed by the `standard' Passarino-Veltman approach: there is not available what is needed for higher loops. We demonstrate our method of how to solve these problems.

hep-ph↗
arXiv2002

Complete electroweak one-loop radiative corrections to top-pair production at TESLA -- a comparison

Electroweak one-loop radiative corrections to the process e^+ e^- -> t tbar are revisited. Two groups from Karlsruhe and Bielefeld/Zeuthen performed independent calculations of both (virtual and soft) QED contributions and weak virtual corrections. For the angular distribution an agreement of at least eight digits for the weak corrections and of at least seven digits for additional photonic corrections is established.

hep-ph↗
arXiv2002

One-loop corrections to the process e+ e- -> t tbar including hard bremsstrahlung

Radiative corrections to the process e+ e- to t tbar are calculated in one-loop approximation of the Standard Model. There exist results from several groups. This talk provides further comparisons of the complete elektroweak contributions, including hard bremsstrahlung. The excellent final agreement of the different groups allows to continue by working on a code for an event generator for TESLA and an extension to e+ e- to 6 fermions.

hep-ph↗
arXiv2001

Electroweak two-loop Sudakov logarithms for on-shell fermions and bosons

We calculate the virtual electroweak Sudakov (double) logarithms at one- and two-loop level for arbitrary on-shell/on-resonance particles in the Standard Model. The associated Sudakov form factors apply in a universal way to arbitrary non-mass-suppressed electroweak processes at high energies, although this universality has to be interpreted with care. The actual calculation is performed in the temporal Coulomb gauge, where the relevant contributions from collinear-soft gauge-boson exchange are contained exclusively in the self-energies of the external on-shell/on-resonance particles. In view of the special status of the time-like components in this gauge, a careful analysis of the asymptotic states of the theory is required. From this analysis we derive an all-order version of the Goldstone-boson Equivalence Theorem without the need for finite compensation factors. By exploiting conditions obtained from non-renormalization requirements, which are a consequence of our choice of gauge, we show that the Sudakov corrections can be extracted through a combination of energy derivatives and projections by means of external sources. We observe that the Standard Model behaves dynamically like an unbroken theory in the Sudakov limit, in spite of the fact that the explicit particle masses are needed at the kinematical (phase-space) level while calculating the Sudakov form factors.

hep-ph↗
arXiv2000

New Insights into the Perturbative Structure of Electroweak Sudakov Logarithms

To match the expected experimental precision at future linear colliders, improved theoretical predictions beyond next-to-leading order are required. At the anticipated energy scale of sqrt(s)=1 TeV the electroweak virtual corrections are strongly enhanced by collinear-soft Sudakov logarithms of the form log^2(s/M^2), with M being the generic mass scale of the W and Z bosons. By choosing an appropriate gauge, we have developed a formalism to calculate such corrections for arbitrary electroweak processes. As an example we consider in this letter the process e^+e^- --> f fbar and study the perturbative structure of the electroweak Sudakov logarithms by means of an explicit two-loop calculation. In this way we investigate how the Standard Model, with its mass gap between the photon and Z boson in the neutral sector, compares to unbroken theories like QED and QCD. In contrast to what is known for unbroken theories we find that the Sudakov logarithms are not exclusively given by the so-called rainbow diagrams, owing to the mass gap and the charged-current interactions. In spite of this, we nevertheless observe that the two-loop corrections are consistent with an exponentiation of the one-loop corrections. In this sense the Standard Model behaves like an unbroken theory at high energies.

hep-ph↗
arXiv2000

Electroweak Sudakov logarithms in the Coulomb gauge

We describe a formalism for calculating electroweak Sudakov logarithms in the Coulomb gauge. This formalism is applicable to arbitrary electroweak processes. For illustration we focus on the specific reactions e^+e^- -> f \bar{f} and e^+e^- -> W_T^+W_T^-, W_L^+W_L^-, which contain all the salient details of dealing with the various types of particles. We discuss an explicit two-loop calculation and have a critical look at the (non-)exponentiation and factorisation properties of the Sudakov logarithms in the Standard Model.

hep-ph↗
arXiv2000

Anomalous triple and quartic gauge boson couplings

This article reviews some recent developments in the analysis of anomalous triple and quartic vector boson couplings that have been discussed at the UK Phenomenology Workshop on Collider Physics 1999 in Durham.

hep-ph↗
arXiv1999

Angular Distribution of Decay Leptons from e^+e^- \to W^+W^- at Threshold

The reaction $ e^+e^- \to W^+W^-$ produces a $W$-boson pair with a non-trivial spin correlation at threshold. This correlation leads to a characteristic angular correlation between the leptons produced in $W^{\pm} \to \ell ^{\pm} ν$ (angles relative to the $e^-$ beam direction): $d σ/d \cos θ_+ d \cos θ_- \sim (1-\cos θ_+) (1+ \cos θ_-) (1+\cos θ_- \cos θ_+) $ . If only the $\ell^-$ is observed, its angular distribution is $d σ/ d \cos θ_- \sim (1+\cos θ_-)(3-\cos θ_-) $, implying a forward-backward asymmetry of 3/8. An analytic result is also given for the azimuthal correlation. These results are reproduced by a Monte Carlo program, that also enables us to study the effects of the $W$ decay width. The threshold behaviour, which stems from the dominance of $ν$-exchange, is contrasted with that due to $γ$- and $Z$-exchange, which is relevant for annihilation in the helicity state $e^-_Re^+_L$.

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