Event Generators for WW Physics
The report summarizes the results of the activities of the Working Group on Event Generators for WW Physics at CERN during 1995.
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arXiv subjects
F. Piccinini
Publications and source records attributed to F. Piccinini.
Electroweak Working Group Report
The report summarizes the results of the activities of the Working Group on Precision Calculations for the Z Resonance at CERN during 1994.
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On the QED Radiator at Order $α^3$
The ${\cal O} (α^3)$ leading logarithmic contribution to the QED radiator in the additive form is considered. The effect of the correction on two-fermion physics at LEP1 and LEP2 is evaluated and critically compared with the one of next-to-leading ${\cal O} (α^2)$ corrections. A critical comparison with existing estimates for the LEP1 energy range is also performed. The ${\cal O} (α^3)$ leading logarithmic corrections turn out to be relevant in view of the experimental precision already reached at LEP1 and foreseen at LEP2.
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Six-Fermion Calculation of Intermediate-mass Higgs Boson Production at Future $e^+ e^-$ Colliders
The production of an intermediate-mass Higgs boson in processes of the kind $e^+ e^- \to 6$ fermions at the energies of future linear colliders is studied. The recently developed and fully automatic algorithm/code ALPHA is used to compute the tree-level scattering amplitudes for the reactions $e^+ e^- \to μ^+ μ^- τ^- \barν_τ u \bar d, μ^+ μ^- e^- \barν_{e} u \bar d$. The code has been interfaced with the Monte Carlo program HIGGSPV/WWGENPV, properly adapted to 6-fermion production, in order to provide realistic results, both in the form of cross sections and event samples at the partonic level. Phenomenological results, that incorporate the effects of initial-state radiation and beamstrahlung, are shown and commented, emphasizing the potentials of full six-fermion calculations for precise background evaluation as well as for detailed studies of the fundamental properties of the Higgs particle.
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Observability at LEP2 hadronic channels of a Z' with small lepton couplings
We consider the effects of a number of models with one extra $Z$, with enhanced couplings to quarks, in the final \underline{hadronic} channels at LEP2. We show that, for a number of representative cases, visible effects could be produced even for very low values of the \underline{lepton} couplings, much smaller than the existing LEP1/SLC and the future LEP2 (lepton channel) bounds.
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WWGENPV 2.0 - A Monte Carlo Event Generator for Four-Fermion Production at e+ e- Colliders
The Monte Carlo program {\tt WWGENPV}, designed for computing distributions and generating events for four-fermion production in $e^+ e^- $ collisions, is described. The new version, 2.0, includes the full set of the electroweak (EW) tree-level matrix elements for double- and single-$W$ production, initial- and final-state photonic radiation including $p_T / p_L$ effects in the Structure Function formalism, all the relevant non-QED corrections (Coulomb correction, naive QCD, leading EW corrections). An hadronisation interface to {\tt JETSET} is also provided. The program can be used in a three-fold way: as a Monte Carlo integrator for weighted events, providing predictions for several observables relevant for $W$ physics; as an adaptive integrator, giving predictions for cross sections, energy and invariant mass losses with high numerical precision; as an event generator for unweighted events, both at partonic and hadronic level. In all the branches, the code can provide accurate and fast results.
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Single-photon signal from neutralinos at LEP2
The production of invisible pairs of lightest neutralinos accompanied by a large-angle hard photon in the reaction $e^+ e^- \to χ^0_1 χ^0_1 γ$ is studied at LEP2 energies. The most general gaugino/higgsino composition of the $χ^0_1$ within the Minimal Supersymmetric Standard Model is assumed. The spectrum of the observed photon is derived within the framework of the $p_t$-dependent structure-function approach, whose accuracy is assessed to be within the foreseen experimental accuracy at LEP2. Higher-order QED corrections due to undetected initial-state radiation are also included. A comparison with the Standard Model main background from $e^+ e^- \to ν\bar νγ$ is performed for optimized photon kinematical cuts. Quantitative conclusions on the signal/background ratio are given for a wide range of values of the SUSY parameters.
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${\cal O} (α^2)$ Next-to-Leading Photonic Corrections to Small-Angle Bhabha Scattering in the Structure Function Formalism
A general method for computing ${\cal O} (α^2)$ and higher-order next-to-leading photonic corrections is presented and applied to the precision calculation of the small-angle Bhabha scattering cross section in the phase-space region of interest for the luminosity measurement at LEP. The formulation is based on a proper matching of exact $\cal O (α)$ results with higher-order corrections in the Structure Function formalism. The results of the approach are analytically compared with theoretical calculations, both for $s$- and $t$-channel processes, available for simple Event Selections. Numerical predictions for realistic Event Selections are also provided and critically compared with the ones existing in the literature.
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The present theoretical error on the Bhabha scattering cross section in the luminometry region at LEP
The results concerning the theoretical evaluation of the small-angle Bhabha Scattering cross section obtained during the Workshop on Physics at LEP2 (CERN, Geneva, Switzerland, 1995) by the Working Group ``Event Generators for Bhabha Scattering'' are summarized. The estimate of the theoretical error on the cross section in the luminometry region is updated.
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Z' Physics
The limits on extra neutral gauge bosons, which could be reached at LEP2, are reviewed. Exclusion and discovery limits are discussed for f\bar f and WW production.
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Event Generators for Bhabha Scattering
The results obtained by the "Event Generators for Bhabha Scattering" working group during the CERN Workshop "Physics at LEP2" (1994/1995) are presented.
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WW Cross-sections and Distributions
We present the results obtained by the "WW Cross-sections and Distributions" working group during the CERN Workshop "Physics at LEP2" (1994/1995)
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Z' Reservation at LC2000
We consider the possibility that one extra $Z\equiv Z'$ exists with a mass of more then two TeV and fermion couplings that do not violate (charged) lepton universality. We show that, in such a situation, a functional relationship is generated between the \underline{deviations} from the SM values of three leptonic observables of two-fermion production at LC 2000 that is completely independent of the values of the $Z'$ mass and couplings. This selects a certain region in the 3-d space of the deviations ($Z'$ "reservation") that is \underline{characteristic} of the model and that would have no observable intersection with analogous regions corresponding to other interesting models of new physics.
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Higgs Physics at LEP2
In this report we review the prospects for Higgs physics at LEP2. The theoretical aspects and the phenomenology of Higgs particles are discussed within the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM). The experimental search techniques are described and the discovery limits for Higgs bosons in the LEP2 energy range are summarized. In addition, opportunities of detecting Higgs particles in non-minimal extensions of the SM and the MSSM are investigated.
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Event Generators for Discovery Physics
Review of Monte Carlo event generators for signals of new particles at LEP2. The areas covered include SUSY, HIGGS and Leptoquarks.
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Searches For New Physics
Review of prospects for discovery of new physics signals at LEP2. The areas covered include SUSY, exotic fermions, BESS models, leptoquarks, virtual effects and CP violating observables.
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Z' Reservation at LEP2
We consider the possibility that one extra $Z\equiv Z'$ exists with arbitrary mass and fermion couplings that do not violate (charged) lepton universality. We show that, in such a situation, a functional relationship is generated between the \underline{deviations} from the SM values of three leptonic observables of two-fermion production at future $e^+e^-$ colliders that is completely independent of the values of the $Z'$ mass and couplings. This selects a certain region in the 3-d space of the deviations that is \underline{characteristic} of the model ($Z'$ "reservation"). As a specific and relevant example, we show the picture that would emerge at LEP2 under realistic experimental conditions.
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SABSPV - A Monte Carlo Integrator for Small-Angle Bhabha Scattering
SABSPV is a code designed to perform a theoretical evaluation of small-angle Bhabha scattering cross sections by suitably matching fixed-order perturbative calculations and structure-function techniques. The implementation of realistic experimental triggering conditions is achieved by using Monte Carlo integration.
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