Radiative Corrections to Boson Pair Production in e+e- Annihilation
The expected accuracy of the experiments of SLC and especially LEP I is a great challenge for theorists to produce adequate predictions for e+e- annihilation into fermion pairs at the Z resonance. Indeed their response for the physics of the Z peak is remarkable: Complete 1-loop calculations and summations of leading higher order terms are available . This opens the possibility for a precise determination of the Z mass — one of the fundamental parameters of the standard model (SM) — and for first accurate tests by measuring the partial and total widths of the Z. Compared to this, physics which is not supported by such a fantastic resonance bonus looks not so exciting, but in any case has its merits. Z physics is directly sensitive only to the more convenient subsector of the SM. Parts like the non-Abelian couplings, the mass generation mechanism can be tested more directly in other reactions. Therefore, W pair production at LEP II will be one of the other fields where parameters of the SM — the W mass, the non-Abelian couplings — can directly be investigated. For the desired accuracy 1-loop corrections are required. Therefore, it is important to have complete O(α) corrections to e+e- → W+W- but also for the annihilation into neutral boson pairs: e+e- → γγ, γZ, ZZ. The cross sections for these processes (see fig. 1.1) are comparable to the μ-pair QED cross section and therefore can be measured with good accuracy. Especially the γγ process is interesting since it is in lowest order still a pure QED reaction. Moreover the radiative corrections to it do not depend on the unknown parameters of the SM like the Higgs mass or the masses of the quarks or the hadronic contribution to the vacuum polarization. Therefore, this process is very clean. Any deviation from the QED (plus its tiny weal: correction) results is the sign for new physics.
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