| 21. |
- Ahmadi, M., et al.
(författare)
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Investigation of the fine structure of antihydrogen
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 578:7795, s. 375-380
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Tidskriftsartikel (refereegranskat)abstract
- At the historic Shelter Island Conference on the Foundations of Quantum Mechanics in 1947, Willis Lamb reported an unexpected feature in the fine structure of atomic hydrogen: a separation of the 2S(1/2) and 2P(1/2) states(1). The observation of this separation, now known as the Lamb shift, marked an important event in the evolution of modern physics, inspiring others to develop the theory of quantum electrodynamics(2-5). Quantum electrodynamics also describes antimatter, but it has only recently become possible to synthesize and trap atomic antimatter to probe its structure. Mirroring the historical development of quantum atomic physics in the twentieth century, modern measurements on anti-atoms represent a unique approach for testing quantum electrodynamics and the foundational symmetries of the standard model. Here we report measurements of the fine structure in the n = 2 states of antihydrogen, the antimatter counterpart of the hydrogen atom. Using optical excitation of the 1S-2P Lyman-alpha transitions in antihydrogen(6), we determine their frequencies in a magnetic field of 1 tesla to a precision of 16 parts per billion. Assuming the standard Zeeman and hyperfine interactions, we infer the zero-field fine-structure splitting (2P(1/2)-2P(3/2)) in antihydrogen. The resulting value is consistent with the predictions of quantum electrodynamics to a precision of 2 per cent. Using our previously measured value of the 1S-2S transition frequency(6,7), we find that the classic Lamb shift in antihydrogen (2S(1/2)-2P(1/2) splitting at zero field) is consistent with theory at a level of 11 per cent. Our observations represent an important step towards precision measurements of the fine structure and the Lamb shift in the antihydrogen spectrum as tests of the charge-parity-time symmetry(8) and towards the determination of other fundamental quantities, such as the antiproton charge radius(9,10), in this antimatter system. Precision measurements of the 1S-2P transition in antihydrogen that take into account the standard Zeeman and hyperfine effects confirm the predictions of quantum electrodynamics.
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| 22. |
- Ahmadi, M., et al.
(författare)
-
Observation of the 1S-2P Lyman-alpha transition in antihydrogen
- 2018
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 561:7722, s. 211-217
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Tidskriftsartikel (refereegranskat)abstract
- In 1906, Theodore Lyman discovered his eponymous series of transitions in the extreme-ultraviolet region of the atomic hydrogen spectrum(1,2). The patterns in the hydrogen spectrum helped to establish the emerging theory of quantum mechanics, which we now know governs the world at the atomic scale. Since then, studies involving the Lyman-alpha line-the 1S-2P transition at a wavelength of 121.6 nanometres-have played an important part in physics and astronomy, as one of the most fundamental atomic transitions in the Universe. For example, this transition has long been used by astronomers studying the intergalactic medium and testing cosmological models via the so-called 'Lyman-alpha forest('3) of absorption lines at different redshifts. Here we report the observation of the Lyman-alpha transition in the antihydrogen atom, the antimatter counterpart of hydrogen. Using narrow-line-width, nanosecond-pulsed laser radiation, the 1S-2P transition was excited in magnetically trapped antihydrogen. The transition frequency at a field of 1.033 tesla was determined to be 2,466,051.7 +/- 0.12 gigahertz (1 sigma uncertainty) and agrees with the prediction for hydrogen to a precision of 5 x 10(-8). Comparisons of the properties of antihydrogen with those of its well-studied matter equivalent allow precision tests of fundamental symmetries between matter ;and antimatter. Alongside the ground-state hyperfine(4,5) and 1S-2S transitions(6,7) recently observed in antihydrogen, the Lyman-alpha transition will permit laser cooling of antihydrogen(8,9), thus providing a cold and dense sample of anti-atoms for precision spectroscopy and gravity measurements(10). In addition to the observation of this fundamental transition, this work represents both a decisive technological step towards laser cooling of antihydrogen, and the extension of antimatter spectroscopy to quantum states possessing orbital angular momentum.
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| 23. |
- Allison, J, et al.
(författare)
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Geant4 developments and applications
- 2006
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Ingår i: IEEE TRANSACTIONS ON NUCLEAR SCIENCE. - 0018-9499. ; 53:1, s. 270-278
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 24. |
- Amole, C., et al.
(författare)
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Autoresonant-spectrometric determination of the residual gas composition in the ALPHA experiment apparatus
- 2013
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 84:6, s. 065110-
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the residual gas composition in the ALPHA experiment apparatus is important in our studies of antihydrogen and nonneutral plasmas. A technique based on autoresonant ion extraction from an electrostatic potential well has been developed that enables the study of the vacuum in our trap. Computer simulations allow an interpretation of our measurements and provide the residual gas composition under operating conditions typical of those used in experiments to produce, trap, and study antihydrogen. The methods developed may also be applicable in a range of atomic and molecular trap experiments where Penning-Malmberg traps are used and where access is limited.
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| 25. |
- Amole, C., et al.
(författare)
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Experimental and computational study of the injection of antiprotons into a positron plasma for antihydrogen production
- 2013
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:4, s. 043510-
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Tidskriftsartikel (refereegranskat)abstract
- One of the goals of synthesizing and trapping antihydrogen is to study the validity of charge-parity-time symmetry through precision spectroscopy on the anti-atoms, but the trapping yield achieved in recent experiments must be significantly improved before this can be realized. Antihydrogen atoms are commonly produced by mixing antiprotons and positrons stored in a nested Penning-Malmberg trap, which was achieved in ALPHA by an autoresonant excitation of the antiprotons, injecting them into the positron plasma. In this work, a hybrid numerical model is developed to simulate antiproton and positron dynamics during the mixing process. The simulation is benchmarked against other numerical and analytic models, as well as experimental measurements. The autoresonant injection scheme and an alternative scheme are compared numerically over a range of plasma parameters which can be reached in current and upcoming antihydrogen experiments, and the latter scheme is seen to offer significant improvement in trapping yield as the number of available antiprotons increases.
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| 26. |
- Amole, C., et al.
(författare)
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Resonant quantum transitions in trapped antihydrogen atoms
- 2012
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 483:7390, s. 439-U86
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom's stature lies in its simplicity and in the accuracy with which its spectrum can be measured(1) and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and-by comparison with measurements on its antimatter counterpart, antihydrogen-the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state(2,3) of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped(4-6) in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.
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| 27. |
- Ahmadi, M., et al.
(författare)
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Enhanced Control and Reproducibility of Non-Neutral Plasmas
- 2018
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 120:2
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Tidskriftsartikel (refereegranskat)abstract
- The simultaneous control of the density and particle number of non-neutral plasmas confined in Penning-Malmberg traps is demonstrated. Control is achieved by setting the plasma's density by applying a rotating electric field while simultaneously fixing its axial potential via evaporative cooling. This novel method is particularly useful for stabilizing positron plasmas, as the procedures used to collect positrons from radioactive sources typically yield plasmas with variable densities and particle numbers; it also simplifies optimization studies that require plasma parameter scans. The reproducibility achieved by applying this technique to the positron and electron plasmas used by the ALPHA antihydrogen experiment at CERN, combined with other developments, contributed to a 10-fold increase in the antiatom trapping rate.
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| 28. |
- Amole, C., et al.
(författare)
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In situ electromagnetic field diagnostics with an electron plasma in a Penning-Malmberg trap
- 2014
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 16, s. 013037-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a novel detection method for the cyclotron resonance frequency of an electron plasma in a Penning-Malmberg trap. With this technique, the electron plasma is used as an in situ diagnostic tool for the measurement of the static magnetic field and the microwave electric field in the trap. The cyclotron motion of the electron plasma is excited by microwave radiation and the temperature change of the plasma is measured non-destructively by monitoring the plasma's quadrupole mode frequency. The spatially resolved microwave electric field strength can be inferred from the plasma temperature change and the magnetic field is found through the cyclotron resonance frequency. These measurements were used extensively in the recently reported demonstration of resonant quantum interactions with antihydrogen.
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| 29. |
- Rülke, A., et al.
(författare)
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The antarctic regional GPS network densification : Status and results
- 2016
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Ingår i: IAG 150 Years proceedings of the 2013 IAG Scientific Assembly, Postdam, Germany, 1-6 September, 2013. - Cham : Springer. - 9783319246031 ; , s. 133-139
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Konferensbidrag (refereegranskat)abstract
- We report on the activities related to the IAG Subcommission 1.3f “Regional Reference Frame for Antarctica”. Campaign-style GPS observations have been carried out since 1995. Based on the Bernese GNSS Software the latest analysis yields results for about 30 stations aligned to the terrestrial reference frame solution IGS08. The obtained station motions are discussed in the context of plate kinematics and glacial-isostatic adjustment. It is demonstrated that the activities are a valuable contribution both to the ITRF densification in Antarctica and to geodynamic research.
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| 30. |
- Solé Navais, Pol, et al.
(författare)
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Genetic effects on the timing of parturition and links to fetal birth weight.
- 2023
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Ingår i: Nature genetics. - 1546-1718. ; 55:4, s. 559-567
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Tidskriftsartikel (refereegranskat)abstract
- The timing of parturition is crucial for neonatal survival and infant health. Yet, its genetic basis remains largely unresolved. We present a maternal genome-wide meta-analysis of gestational duration (n=195,555), identifying 22 associated loci (24 independent variants) and an enrichment in genes differentially expressed during labor. A meta-analysis of preterm delivery (18,797 cases, 260,246 controls) revealed six associated loci and large genetic similarities with gestational duration. Analysis of the parental transmitted and nontransmitted alleles (n=136,833) shows that 15 of the gestational duration genetic variants act through the maternal genome, whereas 7 act both through the maternal and fetal genomes and 2 act only via the fetal genome. Finally, the maternal effects on gestational duration show signs of antagonistic pleiotropy with the fetal effects on birth weight: maternal alleles that increase gestational duration have negative fetal effects on birth weight. The present study provides insights into the genetic effects on the timing of parturition and the complex maternal-fetal relationship between gestational duration and birth weight.
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