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HK: Physik der Hadronen und Kerne
HK 35: Plenary Session
HK 35.1: Plenarvortrag
Donnerstag, 14. März 2002, 08:30–09:00, Plenarsaal
The Muon Magnetic Moment — •Klaus Jungmann1 and on behalf of the muon g-2 collaboration2 — 1Kernfysisch Versneller Instituut, Zernikelaan 25, NL 9747 AA Groningen — 2Brookhaven National Laboratory, Upton, New York, USA
The anomaly of the muon magnetic moment describes the deviation of the particles magnetic g-factor from the value 2 predicted in the Dirac theory for spin 1/2 particles. The quantity can be calculated to very high precision using standard theory. The by far largest contribution arises from Quantum Electrodynamical effects, i.e. photon and lepton fields. There are contributions of some 60 ppm due to hadronic vacuum polarization and some 1.3 ppm from weak interaction. Compared to the electron magnetic anomaly, the muon is more sensitive to the heavier particles by the square of the mass ratio. Therefore, precision calculations and accurate measurements together offer a possibility to search for physics beyond the standard theory. Either hints to yet unknown forces in nature may be gained (in case of disagreement) or parameters in existing speculative models can be significantly bounded (in case of agreement). At the Brookhaven National Laboratory, USA, a magnetic storage ring experiment reached a first result which at the time of publication disagreed with the most recent and most accurate calculations. Careful reevaluations of the theoretical situation were started and are being continued. Of special interset are the hadronic contributions in particular hadronic light by light scattering. The experiment has in the mean time taken more data which is being analyzed. Work in progressing.