Test of time dilation by laser spectroscopy on fast ions

The laser-spectroscopic frequency measurement of Doppler-shifted optical lines in the forward and backward directions of a fast ion beam permits a sensitive test of the relativistic Doppler formula and, hence, the relativistic time-dilation factor γSR = 1/[Formula: see text]. An experiment on 7Li+, stored at a velocity of v = 0.065c in the Heidelberg heavy-ion storage ring TSR, has confirmed time dilation with unprecedented accuracy limiting deviations to below 2.2 × 10–7. Ongoing improvements on the experimental setup will further tighten this limit.PACS Nos.: 03.30.+p, 06.30.Ft, and 42.62.Fi