Physics interest in polarized e+e--reactions at PETRA/PEP energies

After the observation of vertical polarization at PETRA some considerations on its implementation in high-energy physics experiments are given. Vertical beam polarization does not give new information, but the information is obtained easier. Longitudinally polarized beams allow the measurement of electroweak (vector-axialvector) interferences. In the standard model the longitudinal polarization asymmetry is zero for sin2sub(W) = 0.25 for e+e- → μ+μ-, but is + 17% for e+e- → hadrons at 40 GeV c.m. energy. To measure this as a 5 standard deviation effect one needs 4 500 events, i.e. about half-a-year running time. Non-standard models show only small deviations up to 40 GeV, as they are constrained to reproduce the low-energy phenomenology. But significant differences appear at 90 GeV. In QCD the 3-gluon vertex can be observed by the beam-event asymmetry using longitudinally polarized beams. But the effects are small. (orig.)