ZERO-SHIFT TUNING IN GEONIUM BY VARIATION OF TRAPPED CHARGE

Measuring the g factor, or gyromagnetic ratio of an individual electro n or positron permanently confined in ultrahigh vacuum at liquid heliu m temperature, provides one of the few avenues for testing the current ly accepted standard model that views these elementary particles, on t he same level as the quarks, as point-like objects without internal st ructure. Our results, even though their error limits are the smallest ever attained, would still benefit by possibly two orders of magnitude if a shift, estimated at 4 parts in 10(12), caused by interaction of the cyclotron motion with standing electromagnetic waves in the trap c avity confining the electron could be eliminated. Reexamination of exp erimental data obtained in another connection suggests that it is prac tical to identify certain critical cyclotron frequency values for that the shift disappears by testing if the cyclotron frequency measured o n a cloud of electrons does not vary with the number of electrons it c ontains. Clouds here must be kept very much smaller than the wavelengt h of the above standing waves.