Mike Ritter

The hyperfine interval, (DELTA)(nu), of ground state (n = 1) positronium has been measured to high precision yielding (DELTA)(nu) = 203.389 10(74) GHz (3.6 ppm). The technique is similar to that used in all previous measurements. Positronium is formed in a gas in a high static magnetic field which causes pronounced Zeeman splitting of the (‘3)S(,1) state. A microwave field is used to drive transitions between the (‘3)S(,1) levels. The value of (DELTA)(nu), the difference between the (‘3)S(,1) and (‘1)S(,0) states, is derived by extrapolating the measurement to zero static magnetic field and zero gas density.

The present theoretical value for (DELTA)(nu) can be written as (DELTA)(nu) = 203.4003 + a (0.0108) + b (0.0021) GHz where a and b have yet to be fully calculated. The error in the above theoretical expression is about 50 ppm, the size of the uncalculated terms 0((alpha)(‘4)R(,(INFIN))c). When all of the terms of this order are calculated the error should be reduced to a few ppm. The difference between experiment and theory is (DELTA)(nu)(,exp) - (DELTA)(nu)(,th) = -11.2 (+OR-) 10.8 (+OR-) 0.7 MHz where the first error is the theoretical error due to uncalculated terms and the second error is the experimental error.