Ground state hyperfine splitting of hydrogenlike 207Pb81+ by laser excitation of a bunched ion beam in the GSI experimental storage ring

Using a new bunched-beam technique in the GSI heavy-ion experimental storage ring (ESR), we performed precision laser spectroscopy on relativistic heavy ions in the hitherto inaccessible infrared optical region. We determined the wavelength of the M1 transition between the F = 1 (tau approximate to 50 ms) and F = 0 hyperfine states of the Is ground state of hydrogenlike (207)pb(81+) Comparing the result of 1019.7(2) nm with very recent theoretical predictions concerning QED and nuclear size contributions, a disagreement of 4.5 nm is found. Since the nucleus of (207)pb(81+) is well described by the single-particle shell model, uncertainties in nuclear corrections are expected to be small. [S0031-9007(98)07624-8].