The OVAL experiment: A new experiment to measure vacuum magnetic birefringence using high repetition pulsed magnets

A new experiment to measure vacuum magnetic birefringence (VMB), the OVAL experiment, is reported. We developed an original pulsed magnet that has a high repetition rate and applies the strongest magnetic field among VMB experiments. The vibration isolation design and feedback system enable the direct combination of the magnet with a Fabry-P\'erot cavity. To ensure the searching potential, a calibration measurement with dilute nitrogen gas and a prototype search for vacuum magnetic birefringence are performed. Based on the results, a strategy to observe vacuum magnetic birefringence is reported.Comment: 9 pages, 11 figure

Precise measurement of positronium hyperfine splitting using the Zeeman effect

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.Comment: 8 pages, 8 figures, 2 tables, proceeding of LEAP2011, accepted by Hyperfine Interaction