Precision determination of the hyperfine-structure interval in the ground state of positronium. V

Abstract

We report a new, more precise determination of the ground-state hyperfine-structure interval $\Delta \nu$ in positronium, which is based on extensive new data at low ${\mathrm{N}}_2$-gas densities combined with previous data from our group at Yale University. Our experimental value $\Delta \nu =203.389\mathrm{}10\left(74\right)\mathrm{}$ GHz (3.6 ppm) agrees with the current theoretical value $\Delta \nu =203.400\mathrm{}$ GHz, for which the estimated uncertainty is about 50 ppm.