arXiv subjects
Publications and source records attributed to D. Wackeroth.
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.
We briefly present the status of QCD corrections to the inclusive total cross section for the production of a Higgs boson in association with a top-quark pair within the Standard Model at hadron 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.
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 $\MH$.
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.
The impact of theoretical and experimental uncertainties on the indirect determination of the Higgs boson mass, MH, in the Standard Model (SM) is discussed. Special emphasis is put on the electroweak precision observables MW (the W boson mass) and sin^2(theta_eff) (the effective leptonic mixing angle). The current uncertainties of the theoretical predictions for MW and sin^2(theta_eff) due to missing higher order corrections are conservatively estimated to delta MW \approx 7 MeV and delta sin^2(theta_eff) \approx 7 x 10^-5 . Expectations and necessary theoretical improvements for future colliders are explored. Results for the indirect MH determination are presented based on the present experimental and theoretical precisions as well as on improvements corresponding to the prospective situation at future colliders. The treatment of the different future colliders is done in a uniform way in order to allow for a direct comparison of the accuracies that can be reached. Taking all experimental, theoretical, and parametric uncertainties into account, a current upper bound on MH of \sim 200 GeV is obtained. Furthermore we find in a conservative approach that a Linear Collider with GigaZ capabilities can achieve a relative precision of about 8% (or better) in the indirect determination of MH.
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.
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.
We emphasize the role that the associated production of a Higgs boson with a pair of top-antitop quarks can play at present and future hadron colliders. Results of recent calculations of the NLO total cross section for the associated production of a Standard Model like Higgs boson with a pair of top-antitop quarks at the Tevatron (sqrt(s)=2 TeV) are presented.
We present in detail the calculation of the O(alpha_s^3)inclusive total cross section for the process (p pbar-> t tbar h) in the Standard Model, at the Tevatron center-of-mass energy sqrt(s_H)=2 TeV. The next-to-leading order QCD corrections significantly reduce the renormalization and factorization scale dependence of the Born cross section. They slightly decrease or increase the Born cross section depending on the values of the renormalization and factorization scales
We calculate the complete electroweak O(alpha) corrections to pp, pbar p -> l+l- X (l=e, mu) in the Standard Model of electroweak interactions. They comprise weak and photonic virtual one-loop corrections as well as real photon radiation to the parton-level processes q bar q -> gamma,Z -> l+l-. We study in detail the effect of the radiative corrections on the l+l- invariant mass distribution, the cross section in the Z boson resonance region, and on the forward-backward asymmetry, A_FB, at the Fermilab Tevatron and the CERN Large Hadron Collider. The weak corrections are found to increase the Z boson cross section by about 1%, but have little effect on the forward-backward asymmetry in the Z peak region. Threshold effects of the W box diagrams lead to pronounced effects in A_FB at m(l+l-) approx 160 GeV which, however, will be difficult to observe experimentally. At high di-lepton invariant masses, the non-factorizable weak corrections are found to become large.
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.
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.
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.
We summarize the status of calculations of the electroweak radiative corrections to W and Z boson production via the Drell-Yan mechanism at hadron colliders. To fully exploit the precision physics potential of the high-luminosity environment of the Fermilab Tevatron p \bar p (Run II) and the CERN LHC p p colliders, it is crucial that the theoretical predictions are well under control. The envisioned precision physics program includes a precise measurement of the W boson mass and the (leptonic) weak mixing angle, as well as probing the Standard Model (SM) of electroweak interactions at the highest accessible center-of-mass energies. Some numerical results are presented.
We briefly describe the RacoonWW approach to calculate radiative corrections to e+ e- -> W W -> 4 fermions and present numerical results for the total W-pair production cross section at LEP2.
For the envisioned high precision measurement of the W boson mass at the Tevatron and LHC it is crucial that the theoretical predictions for the W and Z production processes are under control. We briefly summarize the status of the electroweak radiative corrections to p p(pbar) -> W -> l nu and p p(pbar) -> Z,gamma -> l+ l- (l=e,mu), and present some numerical results.
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.