Test of Time Dilation Using Stored Li⁺ Ions as Clocks at Relativistic Speed

We present the concluding result from an Ives-Stilwell-type time dilation experiment using ⁷Li⁺ ions confined at a velocity of β=v/c=0.338 in the storage ring ESR at Darmstadt. A Λ-type three-level system within the hyperfine structure of the ⁷Li⁺³S₁ → ³P₂ line is driven by two laser beams aligned parallel and antiparallel relative to the ion beam. The lasers’ Doppler shifted frequencies required for resonance are measured with an accuracy of <4×10−9 using optical-optical double resonance spectroscopy. This allows us to verify the special relativity relation between the time dilation factor γ and the velocity β, γ√1-β²=1 to within ±2.3×10⁻⁹ at this velocity. The result, which is singled out by a high boost velocity β, is also interpreted within Lorentz invariance violating test theories