Electroweak Precision Tests at LEP by Wolfgang Hollik, Günter Duckeck

By Wolfgang Hollik, Günter Duckeck

This assessment provides a quick dialogue of the constitution of the traditional version and its quantum corrections. The predictions for the vector boson lots, the neutrino scattering cross-sections and the Z0 resonance observables are offered. The impression of digital new physics results at the observables is mentioned with the minimum supersymmetric general version taken as an instance. Experimental measurements of electroweak observables are defined just about reviews played on the e+e- collider LEP at energies on the subject of the Z0 height. The theoretical predictions are in comparison with experimental facts and their implications for a standard version are mentioned.

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The two most precise pieces of informations come fl'om the N C / C C neutrino nucleon cross-section ratios [71,72]. 4. The second factor in R , has a very weak dependence on S~v. Hence, measurements of R . can be converted directly into values of m w / m z . 115). 74). Since an increase in mt is equivalent to a shift in s ~ , the relation between R , and ( r o w ~ m s ) a is affected only marginally. This explains qualitatively the stability of m w / m z against variations of mt when extracted from R,.

195) 8socepom Z A complete discussion of radiative corrections requires the calculation of the extra loop diagrams from the non-standard Higgs sector and an extension of the renormalization procedure [10,121,122]. Since m w , m z and sin 2 0w (or P0, equivalently) are now independent parameters, one extra renormalization condition is required. A natural condition would be to define the mixing angle for electrons s~ = s~2 in terms of the ratio of the dressed coupling constants at the Z ~ peak gV - - 1 4s , z -- which is measurable in terms of the left-right or the forward backward asymmetries.

The detection of a light Higgs boson at LEP could be a significant hint of supersymmetry. The structure of the MSSM as a renormalizable quantum field theory allows a complete calculation of the electroweak precision observables similar to that for the Standard Model, in terms of one Higgs mass (usually taken as the CP-odd "pseudoscalar" mass rnA) and t a n ~ = v2/vl, together with the set of SUSY soft-breaking parameters fixing the chargino/neutralino and scalar fermion sectors. It has been known for quite some time [120,126] that light non-standard Higgs bosons as well as light top squarks and charginos predict larger values for the ratio Rb [127,129].

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