Standard Model and Electroweak Interaction: Phenomenology
The status of the LEP 1 results, the LEP 2 perspectives and some recent developments in the high energy behavior of electron-positron annihilation are briefly discussed.
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arXiv subjects
Giampiero Passarino
Publications and source records attributed to Giampiero Passarino.
Standard Higgs Boson Searches at LEP 2
For the first time at LEP most of the events will have four fermions in the finals state and we have the unique opportunity of testing a complete calculation with the experimental data, well beyond the usual approximation of computing production cross section times branching ratios of Higgs into decay products. Calculation of the total cross sections and of different kinds of differential distributions at the partonic level are made available to access the widest information for choosing cuts, for discussing the physics of a standard Higgs boson with a mass around 90 GeV where the Higgs and the Z signal become degenerate and for a comprehensive analysis of the various background components.
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Distributions in Four-Fermion Processes
The programs WPHACT and WTO, which are designed for computing cross sections and other relevant observables in the $e^+e^-$ annihilation into four fermions, are used to make detailed and complete predictions for the semi-leptonic and fully hadronic channels $e^+e^- \to \barq q lν, \barq q \barq q$. Both the total cross sections in the LEP~2 energy range and some of the most relevant distributions are analyzed. Particular algorithms are introduced for the fully hadronic channels in order to analyze the $WW$ physics and to properly define the signal versus the background. With appropriate kinematical cuts it has been shown that the Neutral Current background can be made vanishingly small when the problem of determining the $W$ boson mass is addressed. The remaining background from the complete Charge Current and Mixed processes is again small but not completely negligible. A detailed discussion is performed on the validity of the most relevant approximations such as the double-resonant one. The inclusion of final state QCD correction, in its {\it naive} form (NQCD), is discussed and various implementations are examined.
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LEP1 - LEP2: Theory versus Experiment
The status of the standard model is briefly reviewed in the light of the most recent set of experimental data, with particular emphasis to the limits on the Higgs boson mass. The search for a light Higgs boson at LEP~2 is also briefly analyzed.
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WTO - a deterministic approach to $4$-fermion physics
The program WTO, which is designed for computing cross sections and other relevant observables in the $e^+e^-$ annihilation into four fermions, is described. The various quantities are computed over both a completely inclusive experimental set-up and a realistic one, i.e. with cuts on the final state energies, final state angles, scattering angles and final state invariant masses. Initial state QED corrections are included by means of the structure function approach while final state QCD corrections are applicable in their {\it naive} formulation. A gauge restoring mechanism is included according to the Fermion-Loop scheme. The program structure is highly modular and particular care has been devoted to computing efficiency and speed.
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Stable Calculations for Unstable Particles: Restoring Gauge Invariance
We discuss theoretical and phenomenological aspects of the use of boson propagators with energy-dependent widths in predictions for high-energy scattering processes. In general, gauge invariance is violated in such calculations. We discuss several approaches to restore gauge invariance, necessary for a reliable result. The most promising method is the addition of the relevant parts of the fermionic corrections, which fulfills all Ward identities. The numerical difference between this and other approaches is studied. A number of recommendations are given for LEP2 computations.
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The Top Quark and the Higgs Boson Mass from LEP SLC and CDF Data
The impact of the new experimental data from LEP, SLC and CDF on the top quark mass and the Higgs boson mass is investigated. The determinations of m_{top} and of an upper bound on m_{Higgs} are given, taking into account the experimental error on the QED coupling constant α_{em} and on the b-quark mass m_b. The relevance of higher order theoretical uncertainties is pointed out. briefly reviewed.
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The Z Line-shape in the Standard Model
The status of the theoretical uncertainties for LEP1 observables associated with the corresponding comparison among different codes is briefly reviewed.
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