Positronium is an ideal system for the research of the quantum electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of positronium, $Delta_{mathrm{HFS}}$, gives a good test of the bound state calculations and probes new physics beyond
the Standard Model. A new method of QED calculations has revealed the discrepancy by 15,ppm (3.9$sigma$) of $Delta_{mathrm{HFS}}$ between the QED prediction and the experimental average. There would be possibility of new physics or common systematic uncertainties in the previous all experiments. We describe a new experiment to reduce possible systematic uncertainties and will provide an independent check of the discrepancy. We are now taking data and the current result of $Delta_{mathrm{HFS}} = 203.395,1 pm 0.002,4 (mathrm{stat.}, 12,mathrm{ppm}) pm 0.001,9 (mathrm{sys.}, 9.5,mathrm{ppm}),mathrm{GHz} $ has been obtained so far. A measurement with a precision of $O$(ppm) is expected within a year.
The ground state hyperfine splitting in positronium, $Delta _{mathrm{HFS}}$, is sensitive to high order corrections of QED. A new calculation up to $O(alpha ^3)$ has revealed a $3.9 sigma$ discrepancy between the QED prediction and the experimental r
esults. This discrepancy might either be due to systematic problems in the previous experiments or to contributions beyond the Standard Model. We propose an experiment to measure $Delta_{mathrm{HFS}}$ employing new methods designed to remedy the systematic errors which may have affected the previous experiments. Our experiment will provide an independent check of the discrepancy. The measurement is in progress and a preliminary result of $Delta_{mathrm{HFS}} = 203.399 pm 0.029 mathrm{GHz} (143 mathrm{ppm})$ has been obtained. A measurement with a precision of O(1) ppm is expected within a few years.
