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G. Montagna

Publications and source records attributed to G. Montagna.

At least 91 records · Page 5Linked to original sources
arXiv1997

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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arXiv1996

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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arXiv1996

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.

hep-ph↗
arXiv1996

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.

hep-ph↗
arXiv1996

${\cal O} (α^2)$ 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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arXiv1996

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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arXiv1996

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.

hep-ph↗
arXiv1996

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)

hep-ph↗
arXiv1996

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.

hep-ph↗
arXiv1996

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.

hep-ph↗
arXiv1996

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.

hep-ph↗
arXiv1995

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.

hep-ph↗
arXiv1995

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.

hep-ph↗
arXiv1995

TOPAZ0 2.0 - A Program for Computing De-Convoluted and Realistic Observables Around the $Z^0$ Peak

The program {\tt TOPAZ0} is designed for computing $Z^0$ parameters, de-convoluted and QED-dressed cross sections and forward-backward asymmetries of $e^+ e^-$ annihilation into fermion pairs and of Bhabha scattering around the $Z^0$ peak, over both a completely inclusive experimental set-up and a realistic one, i.e. with cuts on acollinearity, energy or invariant mass and angular acceptance of the outgoing fermions. The new version, 2.0, offers the possibility of imposing different experimental cuts on cross sections and forward-backward asymmetries in a single run, and includes radiative corrections whose effect can become relevant in view of the present and foreseen experimental accuracy. Moreover, an additional option is included, which allows an estimate of the theoretical uncertainty due to unknown higher-order effects, both of electroweak and QCD origin. With respect to the version 1.0, the code is available in the form of {\tt SUBROUTINE}, in order to render more viable the use of the program for aims not planned by the {\tt TOPAZ0} package itself.

hep-ph↗
arXiv1995

Invisible Events with Radiative Photons at LEP

A study of the radiative neutrino counting reaction $e^+ e^- \to ν{\bar ν} γ$ at LEP1 and LEP2 energies is presented. An approximate expression for the spectrum of the observed photon is derived within the framework of the $p_t$-dependent structure function approach. This is compared with an exact expression and found in agreement within the foreseen experimental accuracy. This model describing single-photon radiation can be applied to the more general case of initial-state single-photon emission accompanying invisible final-state events. Higher-order QED corrections due to undetected initial-state radiation are also included. The implementation in a Monte Carlo event generator is briefly described.

hep-ph↗
arXiv1995

WWGENPV - A Monte Carlo Event Generator For Four-Fermion Production in $e^+ e^- \to W^+ W^- \to 4f$

The Monte Carlo program {\tt WWGENPV}, designed for computing distributions and generating events for the four-fermion process $e^+ e^- \to W^+ W^- \to 4f$, is described. It is based on the calculation of the exact tree-level matrix element of the four-fermion reaction and includes initial-state radiation in the leading-log approximation within the structure function approach. The program can be used in a two-fold way: as a Monte Carlo integrator for weighted events, providing predictions for the total cross section, the $W$ invariant-mass distribution, the radiative energy and invariant-mass loss; as a true event generator of unweighted events, useful for simulation purposes.

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