Publications (63)67.5 Total impact
-
Article: Experimental test of special relativity by laser spectroscopy
[show abstract] [hide abstract]
ABSTRACT: The Doppler-free laser-spectroscopic frequency measurement of Doppler-shifted optical lines in forward and backward direction of a fast ion beam permits a sensitive test of the relativistic Doppler-formula and, hence, the relativistic time dilation factor gSR = ( 1 - n2 \mathord/ \vphantom n2 c2 c2 ) - 1 \mathord/ \vphantom - 1 2 2 \gamma _{{SR}} = {\left( {1 - {\nu ^{2} } \mathord{\left/ {\vphantom {{\nu ^{2} } {c^{2} }}} \right. } {c^{2} }} \right)}^{{{ - 1} \mathord{\left/ {\vphantom {{ - 1} 2}} \right. } 2}} . An experiment on metastable 7Li+, stored at a velocity of v = 0.064c in the Heidelberg heavy-ion storage ring TSR, has confirmed time dilation with unprecedented accuracy. Latest tests at two different ion-velocities (v = 0.03c and v = 0.064c) will enhance these measurements. An improved version of this experiment will be carried out at the experimental storage ring (ESR) at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt. The ESR permits 7Li+ to be stored at v = 0.33c which promises an improvement of the sensitivity to deviations from γ SR by an order of magnitude. A first test at the ESR has shown the feasibility for this kind of experiment.Hyperfine Interactions 04/2012; 171(1):57-67. · 0.21 Impact Factor -
Article: Comment on: “Lorentz violation in high-energy ions” by Santosh Devasia
[show abstract] [hide abstract]
ABSTRACT: In an article “Lorentz violation in high-energy ions” by S. Devasia published in this Journal [EPJ C 69, 343 (2010)], 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.European Physical Journal C 04/2012; 71(3):1-2. · 3.63 Impact Factor -
Article: Comment on "Missing Transverse-Doppler Effect in Time-Dilation Experiments with High-Speed Ions"
[show abstract] [hide abstract]
ABSTRACT: 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.02/2011; -
Article: A new measurement of the decay rate of the negative positronium ion:status and preliminary results
[show abstract] [hide abstract]
ABSTRACT: A great number of theoretical papers have been published dealing with the negative positronium ion Ps. On the other hand, experimental data on this purely leptonic three-body system (e+ee) is very limited. Apart from a first observation, a lifetime measurement with an accuracy of 4% has been published. We have built a set-up to produce Ps making use of moderated positrons from a 22Na source, and we are presently running an experiment to improve on its decay rate. This paper discusses the status of the project as well as the possibilities of extending these investigations to other properties of Ps, the latter becoming possible using the NEPOMUC positron source at the FRM II reactor in Munich.PACS No.: 36.10.DrCanadian Journal of Physics 02/2011; 83(4):413-423. · 0.86 Impact Factor -
Article: Test of time dilation by laser spectroscopy on fast ions
[show abstract] [hide abstract]
ABSTRACT: 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/. 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 × 107. Ongoing improvements on the experimental setup will further tighten this limit.PACS Nos.: 03.30.+p, 06.30.Ft, and 42.62.FiCanadian Journal of Physics 02/2011; 83(4):425-434. · 0.86 Impact Factor -
Article: Preparatory measurements for a test of time dilation in the ESR
Canadian Journal of Physics. 01/2011; 89(1):85-93. -
Article: Towards a precision test of time dilation at high velocity
Canadian Journal of Physics. 08/2009; 87(7):749-756. -
Article: Dielectronic Recombination of Fe XXI and Fe XXII via N = 2→N' = 2 Core Excitations
[show abstract] [hide abstract]
ABSTRACT: We have measured dielectronic recombination (DR) resonance strengths and energies for carbon-like Fe XXI forming Fe XX and for boron-like Fe XXII forming Fe XXI via N = 2 → N' = 2 core excitations. All measurements were carried out using the heavy-ion Test Storage Ring at the Max-Planck-Institute for Nuclear Physics in Heidelberg, Germany. We have also calculated these resonance strengths and energies using three independent, state-of-the-art perturbative techniques: a multiconfiguration Breit-Pauli (MCBP) method using the code AUTOSTRUCTURE, a multiconfiguration Dirac-Fock (MCDF) method, and a relativistic configuration interaction method using the Flexible Atomic Code (FAC). Overall, reasonable agreement is found between our experimental results and our theoretical calculations. The most notable discrepancies tend to occur for relative collision energies 3 eV. We have used our measured 2 → 2 results to produce Maxwellian-averaged rate coefficients for Fe XXI and Fe XXII. Our experimentally derived rate coefficients are estimated to be accurate to better than ≈20% both for Fe XXI at kBTe > 0.5 eV and for Fe XXII at kBTe > 0.001 eV. For these results, we provide fits that are accurate to better than 0.5% for Fe XXI at 0.001 eV ≤ kBTe ≤ 10,000 eV and for Fe XXII at 0.02 eV kBTe ≤ 10,000 eV. Our fitted rate coefficients are suitable for ionization balance calculations involving Fe XXI and Fe XXII in photoionized plasmas. Previous published Burgess formula and LS-coupling calculations are in poor agreement with our experimentally derived rate coefficients. None of these published calculations reliably reproduce the magnitude or temperature dependence of our experimental results. Our previously published Fe XXI MCDF results are in good agreement with our experimental results for kBTe 0.07 eV. For both ions in this temperature range our new MCBP, MCDF, and FAC results are in excellent agreement with our experimentally derived rate coefficient.The Astrophysical Journal Supplement Series 12/2008; 147(2):421. · 13.46 Impact Factor -
Article: Dielectronic Recombination of Fe XXIII Forming Fe XXII: Laboratory Measurements and Theoretical Calculations
[show abstract] [hide abstract]
ABSTRACT: We have measured resonance strengths and energies for dielectronic recombination (DR) of beryllium-like Fe XXIII forming boron-like Fe XXII via N = 2 → N' = 2 and N = 2 → N' = 3 core excitations. All measurements were carried out using the heavy-ion Test Storage Ring at the Max Planck Institute for Nuclear Physics (MPI-K) in Heidelberg, Germany. We have also calculated these resonance strengths and energies using three independent, perturbative, state-of-the-art theoretical techniques: the multiconfiguration Breit-Pauli (MCBP) method, the multiconfiguration Dirac-Fock (MCDF) method, and the Flexible Atomic Code (FAC). Overall reasonable agreement is found between our experimental results and these theoretical calculations. We have used our measurements to produce a Maxwellian-averaged DR rate coefficient for Fe XXIII. Our experimentally derived rate coefficient is estimated to be accurate to better that ≈20%. At temperatures where Fe XXIII is predicted to form in both photoionized and electron-ionized gas, we find mixed agreement between our experimental rate coefficient and previously published rate coefficients. We find good agreement at these temperatures between the experimentally derived rate coefficient and our MCBP, MCDF, and FAC results.The Astrophysical Journal 12/2008; 642(2):1275. · 6.02 Impact Factor -
Article: Dielectronic Recombination (via N = 2 → N' = 2 Core Excitations) and Radiative Recombination of Fe XX: Laboratory Measurements and Theoretical Calculations
[show abstract] [hide abstract]
ABSTRACT: We have measured the resonance strengths and energies for dielectronic recombination (DR) of Fe XX forming Fe XIX via N = 2 → N' = 2 (ΔN = 0) core excitations. We have also calculated the DR resonance strengths and energies using the AUTOSTRUCTURE, Hebrew University Lawrence Livermore Atomic Code (HULLAC), Multiconfiguration Dirac-Fock (MCDF), and R-matrix methods, four different state-of-the-art theoretical techniques. On average the theoretical resonance strengths agree to within 10% with experiment. The AUTOSTRUCTURE, MCDF, and R-matrix results are in better agreement with experiment than are the HULLAC results. However, in all cases the 1 σ standard deviation for the ratios of thetheoretical-to-experimental resonance strengths is 30%, which is significantly larger than the estimatedrelative experimental uncertainty of 10%. This suggests that similar errors exist in the calculated levelpopulations and line emission spectrum of the recombined ion. We confirm that theoretical methods based on inverse-photoionization calculations (e.g., undamped R-matrix methods) will severely overestimate the strength of the DR process unless they include the effects of radiation damping. We also find that thecoupling between the DR and radiative recombination (RR) channels is small. Below 2 eV the theoretical resonance energies can be up to ≈30% larger than experiment. This is larger than the estimated uncertainty in the experimental energy scale (0.5% below ≈25 eV and 0.2% forhigher energies) and is attributed to uncertainties in the calculations. These discrepancies makes DR of Fe XX an excellent case for testing atomic structure calculations of ions with partially filled shells. Above 2 eV, agreement between the theoretical and measured energies improves dramatically with the AUTOSTRUCTURE and MCDF results falling within 2% of experiment, the R-matrix results within 3%, and HULLAC within 5%. Agreement for all four calculations improves as the resonance energy increases. We have used our experimental and theoretical results to produce Maxwellian-averaged rate coefficients for ΔN = 0 DR of Fe XX. For kBTe 1 eV, which includes the predicted formation temperatures for Fe XX in an optically thin, low-density photoionized plasma with cosmic abundances, the experimental and theoretical results agree to better than ≈15%. This is within the total estimated experimental uncertainty limits of 20%. Agreement below ≈1 eV is difficult to quantify due to current theoretical and experimental limitations. Agreement with previously published LS-coupling rate coefficients is poor, particularly for kBTe 80 eV. This is attributed to errors in the resonance energies of these calculations as well as the omission of DR via 2p1/2 → 2p3/2 core excitations. We have also used our R-matrix results, topped off using AUTOSTRUCTURE for RR into J ≥ 25 levels, to calculate the rate coefficient for RR of Fe XX. Our RR results are in good agreement with previously published calculations. We find that for temperatures as low as kBTe ≈ 10-3 eV, DR still dominates over RR for this system.The Astrophysical Journal Supplement Series 12/2008; 138(2):337. · 13.46 Impact Factor -
Article: Field Enhanced Dielectronic Recombination of Si11+ and Cl14+ Ions
[show abstract] [hide abstract]
ABSTRACT: The enhancement of dielectronic recombination of multiply charged ions by external electric fields has been studied under controlled conditions. The heavy ion storage rings CRYRING at Stockholm University and the heavy ion storage ring TSR at the Max-Planck-Institut in Heidelberg were used to store beams of Si11+ (ion energy 280 MeV) and Cl14+ (ion energies 250 MeV and 110 MeV), respectively. Recombination in the electron cooler has been measured over energy ranges covering all resonances due to 2s → 2p core exitation. External electric fields up to 183 V/cm at CRYRING and up to 379 V/cm at the TSR have been applied. In the TSR experiment the influence of different magnetic guiding fields as well as the influence of different electron densities in the electron cooler on the recombination rate was investigated. A significant rate enhancement was found for 1s22pnl Rydberg resonances with n > 25 for Si11+ ions and n > 20 for Cl14+ ions.Physica Scripta 11/2006; 1999(T80B):305. · 1.20 Impact Factor -
Article: Photorecombination of Sc3+ and Ti4+ Ions: Search for Interference Effects and Recombination at low Energies
[show abstract] [hide abstract]
ABSTRACT: In search for interference between radiative and dielectronic recombination (RR and DR) absolute recombination rate coefficients for Ar-like Sc3+ and Ti4+ ions have been measured at the Heidelberg heavy ion storage ring TSR. Whereas the Sc3+ experiment suffers from statistics too poor for a line shape analysis, the Ti4+ recombination spectrum clearly does not exhibit asymmetric lineshapes due to quantum mechanical interferences as recently predicted theoretically for Sc3+ ions. The broad Ti3+(3s23p53d2 2F) DR resonance expected on the basis of multi-configuration Hartree-Fock calculations at 3.0 eV with a width of 1.3 eV appears to be shifted towards zero center-of-mass (c. m.) energy, such that its width is larger than its distance to threshold. At zero c. m. energy an unexplained recombination rate enhancement of a factor of 2 beyond the sum of RR and DR rates is observed.Physica Scripta 11/2006; 1999(T80B):314. · 1.20 Impact Factor -
Article: Recombination of F6+ with Free Electrons at Very Low Energies
[show abstract] [hide abstract]
ABSTRACT: Radiative and dielectronic recombination of F6+ have been studied at the heavy ion storage ring TSR in Heidelberg. For a detailed investigation of rate enhancement effects at very low electron-ion center-of-mass energies experimental parameters such as the magnetic guiding field, the electron density and the adiabatic expansion factor of the electron beam have been varied systematically. Whereas measurements at different electron densities show no influence on the enhancement and while a variation of the expansion factor evokes the predicted behaviour, we see an increase of the enhancement with increasing axial magnetic field between 20 mT and 70 mT.Physica Scripta 11/2006; 1999(T80B):298. · 1.20 Impact Factor -
Chapter: Experimental Test of Time Dilation by Laser Spectroscopy on Fast Ion Beams
[show abstract] [hide abstract]
ABSTRACT: The Ives-Stilwell experiment – measuring the time dilation relation γSR = (1 – β 2)–½ – is one of the three classic experiments to test Special Relativity. Together with the interferometric tests of the velocity-independence as well as the isotropy of the speed of light, governed by the Michelson-Morley and the Kennedy-Thorndike experiment, respectively, the Ives-Stilwell experiment entirely establishes Special Relativity on an experimental basis and replaces Einsteins postulates [1]. While the interferometric experiments are ‘nullexperiments’ looking for deviations of the constancy of the speed of light, the time dilation test provides a positive measurement based on a Lorentz boost. It was Einstein who proposed already in 1907 to look for the time dilation effect by observing the Doppler-shifted wavelength of light emitted by excited fast atoms perpendicularly to the motion. In this direction, the classical Doppler effect vanishes leaving pure time dilation. However, it turned out that this scheme is difficult to implement as already small deviations of the observation angle from 90 degree would cause frequency shifts due to the classical Doppler effect which varies linearly around π/2. It took another 31 years until Ives and Stilwell performed the first measurement. Contrary to Einsteins idea they observed the Doppler shifts not perpendicularly but in forward and in backward direction of the atomic motion. This scheme provides different advantages. First, the classical Doppler shift vanishes in this scheme because it is of equal magnitude but opposite in sign in both directions of observation. Secondly, the measurement is less sensitive to small misalignments as the classical Doppler shift varies only quadratically around 0 and π. And finally, as two frequencies are measured, both the time dilation factor as well as the atoms’ velocity can be extracted to an accuracy given by the frequency uncertainty. When observing perpendicularly, the velocity has to be determined separately to provide a test of the time dilation relation. In the next section the principle of the Ives-Stilwell experiment11/2006: pages 479-492; -
Article: Photorecombination of Lithium-like Sc18+ at Threshold: a Challenge for Atomic Structure Theory
[show abstract] [hide abstract]
ABSTRACT: Absolute rates for photorecombination (PR) of lithium-like Sc18+ ions have been measured at the Heidelberg heavy-ion Test Storage Ring (TSR). The investigated electron energy range covers all DR resonances related to 2s → 2p1/2 and 2s → 2p3/2 Δn = 0 core excitations. Resonances associated with 1s2 2p3/2 10ℓj intermediate states are found at energies between 0 and 0.3 eV. They are measured with an energy resolution reaching down to about 18 meV for the lowest-energy resonances. A comparison between the experimental results and calculations based on relativistic many-body perturbation theory (RMTB) yields a good agreement even though deviations at very low energy could not be explained yet.Physica Scripta 08/2006; 2001(T92):376. · 1.20 Impact Factor -
Article: Recombination of Bare Cl17+ Ions in an Electron Cooler
[show abstract] [hide abstract]
ABSTRACT: Using an electron beam merged with an energetic ion beam in a storage ring, non-resonant recombination between multiply charged ions and free electrons is studied by measuring directly the rate of recombination products leaving the interaction zone. The relative electron-ion energy was varied from meV energies up to ~ 50 eV. Above ~ 0.5 eV the measured rates are well represented by the calculated RR into final states up to the experimental Rydberg-ion detection limit. Between ~ 0.01 and 0.5 eV the calculated RR rates are 10% experimental data. As the relative energy is decreased below 0.01 eV, the observed recombination rates rise strongly (to 2.2 times the predicted RR rate), reproducing the low-energy recombination enhancement found in other recent experiments.Physica Scripta 08/2006; 2001(T92):402. · 1.20 Impact Factor -
Article: Dielectronic Recombination of Iron L-Shell Ions
[show abstract] [hide abstract]
ABSTRACT: An experimental program to study low temperature dielectronic recombination (DR) in the iron L-shell ions Fe17+ to Fe23+ is currently in progress at the TSR heavy-ion storage ring in Heidelberg, Germany. L-shell iron ions play an important role in determining the line emission and thermal and ionization structures of cosmic photoionized plasmas. Successful modelling of these plasmas requires accurate ionization and recombination rates, particularly for low temperature DR which is the dominant recombination mechanism for most iron ions in photoionized plasmas. The dependence of DR on the detailed atomic structure makes it challenging to determine the needed DR rate coefficients theoretically, especially in many-electron systems. Our systematic survey of Li- to F-like Fe-ions is designed to produce high-resolution DR spectra which can be used to benchmark theory for ions of increasing complexity and to provide absolute low-temperature DR rates required in astrophysics.Physica Scripta 08/2006; 2001(T92):319. · 1.20 Impact Factor -
Article: Dielectronic recombination resonances in Na8+
[show abstract] [hide abstract]
ABSTRACT: The electron-ion recombination spectrum of the Li-like Na8+ ion in the energy range 0.0–0.5 eV is presented. Experimental results obtained by storage-ring techniques are compared with a calculated spectrum, based on a combination of relativistic many-body methods and complex rotation, and the agreement is found to be very good. The deviations between measured and calculated dielectronic recombination resonance energies are usually below about 2 meV with a maximum difference at 5.5 meV, while the theoretical cross sections deviate by at most 20% from the experiment. The recombination spectrum in the investigated energy region is determined by the 2pj7ℓj′ Rydberg manifold of dielectronic recombination resonances, comprising 61 states within half an eV above the ground state of Na8+. The theoretical resonance parameters of all contributing states are provided.Physical Review A 12/2004; 70:062723. · 2.88 Impact Factor -
Article: Dielectronic recombination resonances in Na{sup 8+}
[show abstract] [hide abstract]
ABSTRACT: The electron-ion recombination spectrum of the Li-like Na{sup 8+} ion in the energy range 0.0-0.5 eV is presented. Experimental results obtained by storage-ring techniques are compared with a calculated spectrum, based on a combination of relativistic many-body methods and complex rotation, and the agreement is found to be very good. The deviations between measured and calculated dielectronic recombination resonance energies are usually below about 2 meV with a maximum difference at 5.5 meV, while the theoretical cross sections deviate by at most 20% from the experiment. The recombination spectrum in the investigated energy region is determined by the 2p{sub j}7l{sub j{sup '}} Rydberg manifold of dielectronic recombination resonances, comprising 61 states within half an eV above the ground state of Na{sup 8+}. The theoretical resonance parameters of all contributing states are provided.Physical Review. A. 11/2004; 70(6). -
Article: Improved test of time dilation in special relativity.
[show abstract] [hide abstract]
ABSTRACT: 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 Deltanu/nu=1 x 10(-9) using collinear saturation spectroscopy. The result confirms the relativistic Doppler formula and sets a new limit of 2.2 x 10(-7) for deviations from the time dilation factor gamma(SR)=(1-v2/c2)(-1/2).Physical Review Letters 12/2003; 91(19):190403. · 7.37 Impact Factor
Top co-authors
Top Journals
Institutions
-
2006–2012
-
University of Manitoba
- Department of Physics and Astronomy
Winnipeg, Manitoba, Canada
-
-
2000–2008
-
Heidelberg University
- Institute of Physics
Heidelberg, Baden-Wuerttemberg, Germany
-
-
1998–2008
-
Max Planck Institute for Nuclear Physics
Heidelberg, Baden-Wuerttemberg, Germany
-
