Measurement of thegFactor of Free, High-Energy Electrons

Abstract

100-kev electrons in 0.1-yusec bunches are sent into a gold foil. The part of the electron bunch which is scattered at right angles, and which, consequently, is partially polarized, is trapped in a magnetic field and held for a measured length of time (up to 300 jusec). The bunch is then released from the trap and allowed to strike a second gold foil. Counters receive the electrons scattered at plus and minus approximately 90°. The cycle is repeated 1000 times per sec. The asymmetry in intensity in the two directions depends upon the final direction of polarization. A plot of the intensity asymmetry vs trapping duration is a cosine curve, whose frequency is the difference between the orbital frequency and the spin precession frequency. This is related to the g factor as follows:coDnioc/Be-a, where g is 2(l+#). Thus the "anomaly/' a, is measured directly. The determination of B presents some difficulty because the field must be slightly nonuniform in order to trap the electrons. The spatial variation in B from the center of the trap to the ends is only 0.3%, and the time average of B which applies to the trapped electrons is evaluated to 0.1%. Measurements made at other electron energies, down to 50 kev, showed a slight dependence of a upon energy. The dependence is attributed to electrostatic charges on the surfaces in the trapping region. The final standard error quoted is, however, purposely made large enough so that the variation of a with energy is bracketted. The result is a=0.0011609±0.0000024.

Spin-Orbital Motion and Thomas Precession in the Classical and Quantum Theories

“…After that the situation has changed. BMT equation successfully confirmed the results of experiments on precision determination of the anomalous magnetic moment of an electron [13,14], muon [15] and also the masses of a number of heavy elementary particles [16]. As it turned out well to explain the experimentally observed effect of radiative self-polarization of electrons [17,18] within the frameworks of the quasiclassical spin theory as well as the Dirac quantum theory.…”

THE MUON g – 2 EXPERIMENTS

“…Table 1 gives a summary of the measurements of a,,. It includes an experiment by Henry, Shrank and Swanson [42] using a long solenoid magnet in analogy with the electron (g-2) experiment of Schupp, Pidd and Crane [41], which we have not described in detail. Table 1 8…”

“…One solution was to scale up the method used at Ann Arbor for the electrons, using a large solenoid and injecting the muons spirally at one end [41]. This was pursued at Berkeley and finally led to a 10% precision measurement [42], At CERN, the work centred on the belief that it should be possible to store muons in a conventional bending magnet with a more or less uniform vertical field between roughly rectangular pole pieces.…”

ftValue ofO14and the Universality of the Fermi Interaction

“…46 The third value results from a verification of the quantum electrodynamic g factor for the muon by a technique similar to the recent electron experiment of Schupp, Pidd, and Crane. 47 This result was combined with the muon magnetic moment measurement of Garwin et al 48 to get the muon mass. It is worth noting that the relations governing the various types of magnetic moment and g factor experiments are derived from the classical covariant equations of motion in a brief but comprehensive note by Bargman, Michel, and Telegdi.…”