DESY Zeuthen/Universität Karlsruhe Team

One of the challenges of Daphne is presented by the measurement of the total e⁺e^- hadronic cross-section, which, through the optical theorem, can give information on the hadronic contributions to _QED(M_Z⁰) and (g-2)_µ. Considerations from precision physics suggest that the goal should be to measure the cross-section at the level of a few percent. This could allow a reduction of the error on a_µ such as to be closer to the contribution from virtual light-by-light scattering. To extract the total cross-section a certain amount of modeling is necessary, since, in contrast to LEP, at low energies the theoretical shape of the total cross-section cannot be calculated from first principles. Important cross-checks will be obtained by studying connections between form-factor measurements at Daphne and tau-lepton decays through isospin and SU(3) relations between multipion final states. More information on electroweak quantities requires models for light-by-light contributions. Various models, such as the Hidden Symmetry Scheme and related models which incorporate vector mesons in chiral Lagrangians, can be used to estimate this hadronic contribution and to compare it with current estimates.

Since a limit to precision measurements in e⁺e^- collisions is due to the presence of QED radiative corrections, the techniques employed for a full evaluation of these effects, will include standard next-to-leading corrections to the second order of QED, leading logarithmic approximations to deal with higher order corrections, and Monte Carlo event generators for data analysis and simulations. Monte Carlo simulations and soft photon summation techniques will also be applied to determine the effects of infrared radiative corrections on the precision, which is attainable in detector calibration through QED processes like quasi-real Compton scattering.

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