Berlin 2005 – scientific programme

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T: Teilchenphysik

T 105: Hauptvortr
äge V

T 105.3: Invited Talk

Wednesday, March 9, 2005, 11:40–12:30, TU H105

Precision Measurements at the Frontiers of Standard Theory: The Magnetic Anomaly of Leptons — •Klaus Jungmann — KVI Groningen

The magnetic anomaly of leptons is dominantly caused by electromagnetic interaction, which can be calculated with sufficient accuracy by Quantum Electrodynamics (QED). For electrons the influence of other known interactions can be neglected in any comparison of theory with presently possible experiments. Recent developments of novel experimental techniques promise therefore that the electromagnetic fine structure constant α can be extracted with unprecedented accuracy. For the heavier leptons, particularly the muon, the influence of other forces has been confirmed for strong and weak interactions. A number of speculative models beyond standard theory would allow for contributions from new interactions and yet unobserved particles. At present, the magnetic anomalies for positive and negative muons are both known to 0.7 ppm from a magnetic storage ring experiment at the Brookhaven National Laboratory, USA. The comparison with theory is hampered by a yet unclear situation in the evaluation of hadronic contributions, which involve measured cross sections for electron-positron annihilation into hadrons or hadronic tauon decays. Several calculations have indicated a possible discrepancy of between 2 and 3 standard deviations, which strongly calls for improvements of experiment and theory. The data of the experiment are also analyzed for possible CPT violations and an improved limit on the permanent electric dipole moment of the muon.