Improved Test of Time Dilation in Special Relativity

An improved test of time dilation in special relativity has been performed using laser spectroscopy on fast ions at the heavy-ion storage-ring TSR in Heidelberg. The Doppler-shifted frequencies of a two-level transition in ⁷Li⁺ ions at $v=0.064c$ have been measured in the forward and backward direction to an accuracy of Δν/ν=1×10^-9 using collinear saturation spectroscopy. The result confirms the relativistic Doppler formula and sets a new limit of 2.2×10^-7 for deviations from the time dilation factor γSR=(1-v²/c²)^-1/2.