B. Botermann

First observation of the ground-state hyperfine transition in 209Bi80+

The long sought after ground-state hyperfine transition in lithium-like bismuth 209Bi80+ was observed for the first time using laser spectroscopy on relativistic ions in the experimental storage ring at the GSI Helmholtz Centre in Darmstadt. Combined with the transition in the corresponding hydrogen-like ion 209Bi82+, it will allow extraction of the specific difference between the two transitions that is unaffected by the magnetic moment distribution in the nucleus and can therefore provide a better test of bound-state QED in extremely strong magnetic fields.

Comment on: “Lorentz violation in high-energy ions” by Santosh Devasia

In an article ”Missing Transverse-Doppler Effect in Time-Dilation Experiments with High-Speed Ions” by S. Devasia [arXiv:1003.2970v1], our recent Doppler shift experiments on fast ion beams are reanalyzed. Contrary to our analysis, Devasia concludes that our results provide an ”indication of Lorentz violation”. We argue that this conclusion is based on a fundamental misunderstanding of our experimental scheme and reiterate that our results are in excellent agreement with Special Relativity. We have performed experiments of the Ives-Stilwell (IS) type [1] that test time dilation of Special Relativity (SR) via the relativistic Doppler shift [2,3,4,5]. A beam of ions, which exhibit an optical transition with a frequency ν0 in their rest frame, is stored at velocity β = v/c in a storage ring. To resonantly excite these ions by a laser at rest in the laboratory frame, the frequency ν of the laser needs to be Doppler shifted according to ν = ν0/γ(1 − β cos θ), where θ is the angle between the laser and the ion beam, measured in the laboratory frame, and γ governs time dilation. For a parallel (θp = 0) or an antiparallel (θa = π) laser beam the frequencies required are νp,a = ν0/γ(1 ∓ β), respectively. Multiplying these two frequencies and using γ = (1 − β) as predicted by SR results in νpνa/ν 2 0 = 1, (1) i.e. the geometric mean of the Doppler shifted frequencies equals the rest frame frequency for all velocities β. In one of our implementations of the IS experiment saturation spectroscopy is used by overlapping simultaneously a parallel and antiparallel laser beam with the ion beam to select a narrow velocity class β0 within the ions’ velocity distribution. The parallel laser is held fixed at the laser frequency νp = ν0/γ(1 − β0) and is resonant with ions at β0, while the other laser is scanned over the velocity distribution. The fluorescence yield, measured with a photomultiplier (PMT) located around 90 degree with respect to the ion beam, will exhibit a minimum (a Lamb dip) when the antiparallel laser talks to the same velocity class β0, i.e. when its frequency is at νa = ν0/γ(1 + β0). SR thus predicts the Lamb dip to occur when Eq. 1 is fulfilled, which is shown to be confirmed by our experiments to an accuracy of < 2 × 10 on Li ions at β0 = 0.03 and β0 = 0.06 [3]. S. Devasia [6] claims that the Doppler shift of the emitted light has to be taken into account and replaces ν0 in Eq. 1 by γν0, i.e. by the frequency of the light detected exactly at θ = π/2. This is a misconception of our experimental measurement scheme. While it is true that the detected light is Doppler-shifted, this Doppler shift is irrelevant for the analysis. Neither do we measure the frequency ν0 β 0 PMT ν a =ν 0 /γ(1+β 0 ) IF ν p =ν 0 /γ(1−β 0 ) of the emitted light nor do we intend to observe at exactly right angle. We only record the number of re-emitted photons as a function of the scanning laser frequency to monitor the Lamb dip caused by the simultaneous resonance of both lasers with the same ions. Thus the angle of detection is irrelevant but θ ≈ π/2 helps to separate fluorescence from laser stray light. In fact, stray light suppression is the only reason for using an interference filter (IF) in front of the PMT; its transmission width of 10 nm corresponds to 10 THz, about 10 times broader than the width of the Lamb dip, and a factor of 10 larger than the transverse Doppler shift (at β = 0.064). None of the filters employed in our experiments [2,3,4,5] to improve the signal-to-noise ratio in the fluorescence light detection are affecting the shape and position of the signal indicating the resonance of the parallel and antiparallel laser with the same velocity class β0. The frequency ν0 occurring in Eq. 1 has nothing to do with the frequency of the emitted light in our experiment, but is the rest frame frequency ν0 deduced from experiments at smaller ion velocities [3,7]. In conclusion, SR predicts Eq. 1 as the outcome of our experiments, which is confirmed with high accuracy.

Preparatory measurements for a test of time dilation in the ESR

We present preparatory measurements for an improved test of time dilation at the experimental storage ring (ESR) at GSI in Darmstadt. A unique combination of particle accelerator experiments and laser spectroscopy is used to perform this test with the highest precision. 7Li+ ions are accelerated to 34% of the speed of light at the GSI Helmholtzzentrum fur Schwerionenforschung and stored in the experimental storage ring. The forward and backward Doppler shifts of an electric dipole transition of these ions are measured with laser spectroscopy techniques. From these Doppler shifts, both the ion velocity β = ν/c and the time dilation factor γ=γSR(1+αˆβ2) can be derived for testing Special Relativity. Two laser systems have been developed to drive the 3S1→3P2 transition in 7Li+. Moreover, a detector system composed of photomultipliers, both to monitor the exact laser ion beam overlap as well as to optimize fluorescence detection, has been set up and tested. We investigate optical-optical double-resonance spec...

Modern Ives-Stilwell Experiments At Storage Rings: Large Boosts Meet High Precision

We give a brief overview of time dilation tests using high-resolution laser spectroscopy at heavy-ion storage rings. We reflect on the various methods used to eliminate the first-order Doppler effect and on the pitfalls encountered, and comment on possible extensions at future facilities providing relativistic heavy ion beams at

Testing Time Dilation on Fast Ion Beams

\gamma \gg 1

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

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Observation of the hyperfine transition in lithium-like bismuth Bi-209(80+) : Towards a test of QED in strong magnetic fields

We report the status of an experimental test of time dilation in Special Relativity. This is accomplished by simultaneously measuring the forward and backward Doppler shifts of an electronic transition of fast moving ions, using high-precision laser spectroscopy. From these two Doppler shifts both the ion velocity ? = v/c and the time dilation factor can be derived. From measurements based on saturation spectroscopy on lithium ions stored at ? = 0.03 and ? = 0.06 in the TSR heavy-ion storage ring, we achieved an upper limit for a [?2] deviation from Special Relativity of . In recent measurements on a ? = 0.34 Li+ beam in the ESR storage ring we used optical-optical double-resonance spectroscopy which, in combination with the TSR result, gives improved sensitivity on the [?4] term of . We discuss current limitations and possible improvements that promise an enhancement of the sensitivity by at least one order of magnitude in the future.