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R. Pittau

Publications and source records attributed to R. Pittau.

71 records · Page 4Linked to original sources
arXiv1998

WEXTER and ERAFITTER: two programs to fit M_W at LEP2 using the best measurable kinematical variables

In this paper, we present two programs to fit M_W at LEP2 using the best measurable kinematical variables. The theoretical probabilities of observing the final-state kinematical configurations are computed by integrating over the quantities that are not well measured. Therefore, an event-by-event kinematical reconstruction is avoided. M_W is then determined through a maximum likelihood fit.

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arXiv1997

On the determination of M_W and TGCs in W-pair production using the best measured kinematical variables

A study is made of the feasibility of maximum likelihood fits to determine M_W and triple gauge boson couplings using only those experimental kinematical variables that are well measured. A computational tool to calculate theoretical probabilities for those kinematical variables is discussed and then applied to samples of unweighted events produced by an event generator. Detailed results on the M_W determination for semileptonic final states in W-pair production show the feasibility of the method. For TGCs one result is presented as an illustration.

hep-ph↗
arXiv1997

QCD corrections to $e^+ e^- \to u~\bar d~s~\bar c$ at Lep 2 and the Next Linear Collider: CC11 at O(α_s)

QCD one-loop corrections to the full gauge invariant set of electroweak diagrams describing the hadronic process $e^+ e^- \to u~\bar d~s~\bar c$ are computed. Four-jet shape variables for $WW$ events are studied at next-to-leading order and the effects of QCD corrections on the determination of the $W$--mass in the hadronic channel at Lep 2 and NLC is discussed. We compare the exact calculation with a ``naive''approach to strong radiative corrections which has been widely used in the literature.

hep-ph↗
arXiv1997

QCD corrections to charged current processes at the Next Linear Collider: CC10, CC11 and CC20 at O(alpha_s)

One-loop QCD corrections to the full gauge invariant set of electroweak diagrams describing the charged current processes $e^+ e^- \to u \bar d μ\barν_μ$ (CC10), $e^+ e^- \to u \bar d e^- \barν_e$ (CC20) and $e^+ e^- \to u \bar d s \bar c$ (CC11) are computed. We compare the exact calculation with a ``naive''approach to strong radiative corrections which has been widely used in the literature and discuss the phenomenological relevance of QCD corrections for NLC physics.

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arXiv1997

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.

hep-ph↗
arXiv1997

A simple method for multi-leg loop calculations

In this paper, I present a technique to simplify the tensorial reduction of one-loop integrals with arbitrary internal masses, but at least two massless external legs. By applying the method to rank l tensor integrals, one ends up with at most rank 1 tensor functions with the initial number of denominators, plus tensor integrals with less denominators and rank < l. To illustrate the algorithm, I explicitly compute diagrams contributing to processes of physical interest and show how the usual numerical instabilities due to the appearance of Gram determinants can be controlled.

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arXiv1996

LEP2 physics and event generators

The present status of four-fermion calculations and event generators for LEP2 physics is reviewed. Perspectives for future improvements are given.

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arXiv1996

Final state QCD corrections to off-shell single top production in hadron collisions

In this paper, I study final state QCD radiative corrections to off-shell single top production via decaying $W$ at hadron collider energies. The tree level Breit-Wigner distribution of the produced top invariant mass is distorted by final state QCD radiation, while the peak position remains unchanged. The exact one loop QCD calculation and the narrow width approximation agree in predicting the cross section, the hadronic transverse energy distribution and the bottom-lepton invariant mass distribution.

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↗
arXiv1994

EXCALIBUR -- a Monte Carlo program to evaluate all four fermion processes at LEP 200 and beyond

A Monte Carlo program is presented that computes all four fermion processes in $e^+ e^-$ annihilation. QED initial state corrections and QCD contributions are included. Fermions are taken to be massless, allowing a very fast evaluation of the matrix element. A systematic, modular and self-optimizing strategy has been adopted for the Monte Carlo integration, that serves also as an example for further event generators in high energy particle physics.

hep-ph↗
arXiv1994

Four quark processes at LEP 200

In this paper I investigate the production of four quarks at LEP 200 energies. Effects due to initial state QED corrections and background diagrams, including QCD contributions, are studied and examples of results obtained with an event generator presented.

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arXiv1994

Four fermion production in e+ e- annihilation

Four fermion processes at e+ e- colliders in a range of energy from 100 GeV to 1 TeV are discussed and examples of results obtained with an event generator presented. We also investigate the effects of the inclusion of initial state QED corrections and QCD contributions.

hep-ph↗
arXiv1994

Initial-state QED corrections to four-fermion production in e+e- collisions at LEP200 and beyond

The implementation of QED initial-state radiative corrections in the process of four-fermion production at LEP200 and higher-energy e+e- colliders is discussed. Because of the presence of charged-current processes, this is a nontrivial problem, and we compare our approach with other existing treatments. We describe the Monte Carlo algorithm used for the generation of 4-fermion events with photon bremsstrahlung. Comparison between our event generator and semi-numerical calculations are presented, as well as predictions for W and Z pair related cross sections.

hep-ph↗
arXiv1994

Weight optimization in multichannel Monte Carlo

We discuss the improvement in the accuracy of a Monte Carlo integration that can be obtained by optimization of the `a-priori weights' of the various channels. These channels may be either the strata in a stratified-sampling approach, or the several `approximate' distributions such as are used in event generators for particle phenomenology. The optimization algorithm does not require any initialization, and each Monte Carlo integration point can be used in the evaluation of the integral. We describe our experience with this method in a realistic problem, where an effective increase in program speed by almost an order of magnitude is observed.

hep-ph↗
arXiv1994

All electroweak four fermion processes in electron-positron collisions

This paper studies the electroweak production of all possible four fermion states in e+ e- collisions. Since the methods employed to evaluate the complete matrix elements and phase space are very general, all four fermion final states in which the charged particles are detected can be considered. Also all kinds of experimental cuts can be imposed. With the help of the constructed event generator a large number of illustrative results is obtained, which show the relevance of backgrounds to a number of signals. For LEP 200 the W-pair signal and its background are discussed, for higher energies also Z-pair and single W and Z signals and backgrounds are presented.

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