Heidelberg 1999 – scientific programme
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T: Teilchenphysik
T 701: Post-deadline session 1
T 701.1: Talk
Friday, March 19, 1999, 14:00–14:15, CH1
First Result from a New Measurement of the Positive Muon Magnetic Anomaly — •Klaus Jungmann1, Alex Grossmann1, Matthias Grosse-Perdekamp2, Ulrich Haeberlen3, Axel Steinmetz2, Jörg Pretz2, Ralf Prigl4, Gisbert zu Putlitz1, and David Urner5 — 1Physikalisches Institut, Universität Heidelberg — 2Physics Department, Yale University — 3MPI für Med. Forschung, Heidelberg — 4Brookhaven National Laboratory — 5Department of Physics, University of Illinois
A new and improved experiment for a precise measurement of the muon magnetic anomaly aµ was successfully started at the Brookhaven National Laboratory (BNL) and has obtained a first result. The difference between the cyclotron and the spin precession frequencies is measured employing 3.09 GeV/c muons stored in a 1.45 T highly homogeneous magnetic field. The positrons from the decay µ+ → e+ νe νµ constitute our signal and are detected with lead-scintillating fiber calorimeters placed inside of the storage ring. The high energy e+ are preferentially emitted along the muon spin direction and the muon spin precession is reflected in the decay positron time spectrum as determined through observing positrons exceeding a threshold energy. New major components of the experiment compared to conceptually similar earlier projects carried out at CERN include a superferric magnetic storage ring, a superconducting dc inflector, electrostatic quadrupoles, lead-scintillating fiber electron calorimeters and a high precision NMR magnetic field measurement and control system. A first measurement from a startup run yields aµ = 1 165 925(15) × 10−9. This value is similar in accuracy and in good agreement with previous results for µ+ at CERN and with standard theory calculations, which are accurate to 0.66 ppm. The theory is limited by hadronic vacuum polarization which can be determined from measurements of e+ - e− annihilation into hadrons and hadronic τ-decays. Experiments at Novosibirsk (BINP), Beijing (BES), Frascati (DAΦNE) and at Cornell (CLEO) promise a substantial improvement of the knowledge of the hadronic contributions. A novel magnetic muon kicker has been installed and commisioned recently in order to boost significantly the number of stored muons. The data acquired since is expected to lower the uncertainty in aµ. First extensive data-taking is scheduled to start early in 1999. The experiment aims for a precision of 0.35 ppm at which contributions to the magnetic anomaly arising from weak interaction can be tested significantly and where a sensitivity to effects from physics beyond the standard model, for example from super symmetry, exists.