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A. Denner

Publications and source records attributed to A. Denner.

At least 73 records · Page 4Linked to original sources
arXiv2003

Electroweak radiative corrections to e+ e- -> nu nubar H

The complete electroweak O(alpha) radiative corrections to the Higgs-boson production processes e+ e- -> nu_l anti-nu_l H (l=e,mu,tau) are calculated in the electroweak Standard Model. For e+ e- -> nu_e anti-nu_e H, where ZH production and W-boson fusion contribute, both production channels are added coherently. The calculation of the corrections is described in some detail including, in particular, the treatment of the Z-boson resonance in the ZH-production channel. The discussion of numerical results focusses on the total cross section as well as on angular and energy distributions of the Higgs boson. In the Gmu-scheme, the bulk of the corrections is due to initial-state radiation. The corrections turn out to reduce the total cross section by \sim 10% for high energies, where the W-boson fusion dominates. In this region, the corrections depend only weakly on the energy and the production angle of the Higgs boson. Based on an analysis of the leading universal corrections, a simple improved Born approximation is introduced. This approximation describes the corrected cross section within about 3%.

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arXiv2003

Two-loop electroweak angular-dependent logarithms at high energies

We present results on the two-loop leading and angular-dependent next-to-leading logarithmic virtual corrections to arbitrary processes at energies above the electroweak scale. In the `t Hooft-Feynman gauge the relevant Feynman diagrams involving soft and collinear gauge bosons γ, Z, W^\pm coupling to external legs are evaluated in the eikonal approximation in the region where all kinematical invariants are much larger than the electroweak scale. The logarithmic mass singularities are extracted from massive multi-scale loop integrals using the Sudakov method and alternatively the sector-decomposition method in the Feynman-parameter representation. The derivations are performed within the spontaneously broken phase of the electroweak theory, and the two-loop results are in agreement with the exponentiation prescriptions that have been proposed in the literature based on a symmetric SU(2) x U(1) theory matched with QED at the electroweak scale.

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arXiv2002

Reduction of one-loop tensor 5-point integrals

A new method for the reduction of one-loop tensor 5-point integrals to related 4-point integrals is proposed. In contrast to the usual Passarino-Veltman reduction and other methods used in the literature, this reduction avoids the occurrence of inverse Gram determinants, which potentially cause severe numerical instabilities in practical calculations. Explicit results for the 5-point tensor coefficients are presented up to rank 4. The expressions for the reduction of the relevant 1-, 2-, 3-, and 4-point tensor coefficients to scalar integrals are also included; apart from these standard integrals no other integrals are needed.

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arXiv2002

Challenges in W-pair production

The investigation of W-pair production offers unique precision tests of the electroweak theory at future e+e- colliders, including precise determinations of cross sections, the W-boson mass, and gauge-boson self-couplings. The state-of-the-art and future requirements in the theoretical prediction for the reaction e+e- -> WW -> 4f(+gamma) are briefly reviewed.

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arXiv2002

RacoonWW1.3: A Monte Carlo program for four-fermion production at e^+ e^- colliders

We present the Monte Carlo generator RacoonWW that computes cross sections to all processes e^+ e^- -> 4f and e^+ e^- -> 4f + gamma and calculates the complete O(alpha) electroweak radiative corrections to e^+ e^- -> W W -> 4f in the electroweak Standard Model in double-pole approximation. The calculation of the tree-level processes e^+ e^- -> 4f and e^+ e^- -> 4f + gamma is based on the full matrix elements for massless (polarized) fermions. When calculating radiative corrections to e^+ e^- -> W W -> 4f the complete virtual doubly-resonant electroweak corrections are included, i.e. the factorizable and non-factorizable virtual corrections in double-pole approximation, and the real corrections are based on the full matrix elements for e^+ e^- -> 4f + gamma. The matching of soft and collinear singularities between virtual and real corrections is done alternatively in two different ways, namely by using a subtraction method or by applying phase-space slicing. Higher-order initial-state photon radiation and naive QCD corrections are taken into account. RacoonWW also provides anomalous triple gauge-boson couplings for all processes e^+ e^- -> 4f and anomalous quartic gauge-boson couplings for all processes e^+ e^- -> 4f + gamma.

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arXiv2002

Present and Future Electroweak Precision Measurements and the Indirect Determination of the Mass of the Higgs Boson

We discuss the experimental and theoretical uncertainties on precision electroweak observables and their relationship to the indirect constraints on the Higgs-boson mass, $\MH$, in the Standard Model (SM). The critical experimental measurements ($\MW$, $\sweff$, $\mt$, ...) are evaluated in terms of their present uncertainties and their prospects for improved precision at future colliders, and their contribution to the constraints on $\MH$. In addition, the current uncertainties of the theoretical predictions for $\MW$ and $\sweff$ due to missing higher order corrections are estimated and expectations and necessary theoretical improvements for future colliders are explored. The constraints from rare B decays are also discussed. Analysis of the present experimental and theoretical precisions yield a current upper bound on $\MH$ of $\sim 200$ GeV. Including anticipated improvements corresponding to the prospective situation at future colliders (Tevatron Run II, LHC, LC/GigaZ), we find a relative precision of about 25% to 8% (or better) is achievable in the indirect determination of $\MH$.

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arXiv2002

On Theoretical Uncertainties of the W Angular Distribution in W-Pair Production at LEP2 Energies

We discuss theoretical uncertainties of the distribution in the cosine of the W polar angle projected into a measurement of the anomalous triple gauge-boson coupling λ=λ_γ=λ_Z at LEP2 energies for the tandem of the Monte Carlo event generators KoralW and YFSWW3 and for the Monte Carlo event generator RacoonWW. Exploiting numerical results of these programs and cross-checks with experimental fitting procedures, we estimate that the theoretical uncertainty of the value of λdue to electroweak corrections, as obtained at LEP2 with the help of these programs, is ~0.005, about half of the expected experimental error for the combined LEP2 experiments (~0.010). We use certain idealized event selections; however, we argue that these results are valid for realistic LEP2 measurements.

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arXiv2001

Status and Prospects of Theoretical Predictions for Weak Gauge Boson Production Processes at Lepton and Hadron Colliders

For the envisioned precision measurement of the W-boson mass at present and future lepton and hadron colliders it is crucial that the theoretical predictions for the underlying production processes are well under control. We briefly describe the status of the predictions for the W-pair-production processes at e+ e- colliders, e+ e- -> W+ W- -> 4f, and for W- and Z-boson production at pp and p anti-p colliders, pp, p anti-p -> W -> l nu_l and pp, p anti-p -> Z,gamma -> l+ l- (l=e,mu). We also discuss the theoretical improvements needed to meet the experimental accuracies one hopes to achieve in future experiments.

hep-ph↗
arXiv2001

Precise predictions for e+e- --> 4f(+gamma) with anomalous couplings

The relevance of radiative corrections to 4f production at LEP2 and future e+e- colliders is emphasized, and their treatment in the event generator RacoonWW is briefly discussed. In particular, the non-universal corrections are compared with the signature of anomalous triple gauge-boson couplings. For 4f+gamma production the influence of anomalous quartic gauge-boson couplings on photon-energy distributions is illustrated.

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arXiv2001

Probing anomalous quartic gauge-boson couplings via e+e- --> 4fermions+gamma

All lowest-order amplitudes for e+e- --> 4f+gamma are calculated including five anomalous quartic gauge-boson couplings that are allowed by electromagnetic gauge invariance and the custodial SU(2)_c symmetry. Three of these anomalous couplings correspond to the operators L_0, L_c, and L_n that have been constrained by the LEP collaborations in WWgamma production. The anomalous couplings are incorporated in the Monte Carlo generator RACOONWW. Moreover, for the processes e+e- --> 4f+gamma RACOONWW is improved upon including leading universal electroweak corrections such as initial-state radiation. The discussion of numerical results illustrates the size of the leading corrections as well as the impact of the anomalous quartic couplings for LEP2 energies and at 500GeV.

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arXiv2001

Off-shell W-pair production - universal versus non-universal corrections

Electroweak radiative corrections to e+e- scattering processes typically amount to O(10%) at LEP energies. Their logarithmic increase with energy renders them even more important at future colliders. Although the bulk of these corrections is due to universal process-independent effects, the remaining non-universal corrections are nevertheless phenomenologically important. We describe the structure of the universal corrections to e+e- --> WW --> 4f in detail and discuss the numerical size of universal and non-universal effects using the Monte Carlo generator RACOONWW.

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arXiv2001

Predictions for e+ e- -> WW -> 4f(gamma) at a future linear collider

We describe the salient features of precise predictions for the processes e+ e- -> WW -> 4f(gamma) as obtained with the Monte Carlo generator RacoonWW, including the complete O(alpha) electroweak radiative corrections in the double-pole approximation. Numerical results for some distributions are given at the typical linear-collider energy \sqrt{s}=500 GeV. Moreover, we study the impact of the non-universal electroweak corrections by comparing with results of an improved Born approximation.

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arXiv2000

Electroweak Precision Physics at e+ e- Colliders with RacoonWW

We present precise predictions for the processes e+ e- -> WW -> 4f(gamma) at LEP2 and future Linear-Collider (LC) energies obtained with the Monte Carlo generator RacoonWW. The program RacoonWW includes the complete O(alpha) electroweak radiative corrections to e+ e- -> WW -> 4f in the double-pole approximation (DPA). While the virtual corrections are treated in DPA, the calculation of the bremsstrahlung corrections is based on the full lowest-order matrix elements to the processes e+ e- -> 4f+gamma. This asymmetric treatment of virtual and real photons requires a careful matching of the arising infrared and collinear singularities. We also take into account higher-order initial-state photon radiation via the structure-function method. Here, we briefly describe the RacoonWW approach, give numerical results for the total W-pair production cross sections, confront them with LEP2 data, and study the impact of the radiative corrections on angular and W-invariant-mass distributions at LEP2 and LC energies.

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arXiv2000

Electroweak radiative corrections to e+e- --> WW --> 4fermions in double-pole approximation -- the RACOONWW approach

We calculate the complete O(alpha) electroweak radiative corrections to e+e- --> WW --> 4f in the electroweak Standard Model in the double-pole approximation. We give analytical results for the non-factorizable virtual corrections and express the factorizable virtual corrections in terms of the known corrections to on-shell W-pair production and W decay. The calculation of the bremsstrahlung corrections, i.e. the processes e+e- --> 4f+gamma in lowest order, is based on the full matrix elements. The matching of soft and collinear singularities between virtual and real corrections is done alternatively in two different ways, namely by using a subtraction method and by applying phase-space slicing. The O(alpha) corrections as well as higher-order initial-state photon radiation are implemented in the Monte Carlo generator RACOONWW. Numerical results of this program are presented for the W-pair-production cross section, angular and W-invariant-mass distributions at LEP2. We also discuss the intrinsic theoretical uncertainty of our approach.

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arXiv2000

Radiative corrections to e+e- --> WW --> 4f 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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arXiv2000

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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