The ASACUSA-Cusp collaboration has recently upgraded the positron system to improve the production of antihydrogen. Previously, the experiment suffered from contamination of the vacuum in the antihydrogen production trap due to the transfer of positrons from the high pressure region of a buffer gas trap. This contamination reduced the lifetime of antiprotons. By adding a new positron accumulator and therefore decreasing the number of transfer cycles, the contamination of the vacuum has been reduced. Further to this, a new rare gas moderator and buffer gas trap, previously used at the Aarhus University, were installed. Measurements from Aarhus suggested that the number of positrons could be increased by a factor of four in comparison to the old system used at CERN. This would mean a reduction of the time needed for accumulating a sufficient number of positrons (of the order of a few million) for an antihydrogen production cycle. Initial tests have shown that the new system yields a comparable number of positrons to the old system.

C. Amslera, D. Barnab, H. Breukerc, M. Bumbara, S. Chesnevskayaa, G. Costantinid, R. Ferragute, M. Giammarchif , A. Gligorovaa, G. Gostad, H. Higakig, M. Horih,i∗, E. D. Huntera, Y. Kanaij , C. Killiana, V. Kletzla, V. Kraxbergera, N. Kurodak, A. Lanza, M. Lealid, V. Mäckela,c, G. Maerol, C. Malbrunotm, V. Mascagnad, Y. Matsudak, S. Miglioratid, D. J. Murtagha, Y. Nagatan, A. Nandaa, L. Nowakm, F. Parnefjord Gustafssona, E. Pasinol, W. Pirklh, M. Romél, M. C. Simona, M. Tajimaj , V. Tosoe, U. Uggerhøjo, S. Ulmerc, L. Venturellid, A. Weisera, E. Widmanna∗, T. Wolzm, Y. Yamazakic, J. Zmeskala

Magnetized nonneutral plasma composed of electrons or positrons couples to the local microwave environment via cyclotron radiation. The equilibrium plasma temperature depends on the microwave energy density near the cyclotron frequency. Fine copper meshes and cryogenic microwave absorbing material were used to lower the effective temperature of the radiation environment in ASACUSA's Cusp trap, resulting in significantly reduced plasma temperature.

The ASACUSA collaboration produces a beam of antihydrogen atoms by mixing pure positron and antiproton plasmas in a strong magnetic field with a double cusp geometry. The positrons cool via cyclotron radiation inside the cryogenic trap. Low positron temperature is essential for increasing the fraction of antihydrogen atoms which reach the ground state prior to exiting the trap. Many experimental groups observe that such plasmas reach equilibrium at a temperature well above the temperature of the surrounding electrodes. This problem is typically attributed to electronic noise and plasma expansion, which heat the plasma. The present work reports anomalous heating far beyond what can be attributed to those two sources. The heating seems to be a result of the axially open trap geometry, which couples the plasma to the external (300 K) environment via microwave radiation.

The ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration plans to measure the ground-state hyperfine splitting of antihydrogen in a beam at the CERN Antiproton Decelerator with initial relative precision of 10-6 or better, to test the fundamental CPT (combination of charge conjugation, parity transformation and time reversal) symmetry between matter and antimatter. This challenging goal requires a polarised antihydrogen beam with a sufficient number of antihydrogen atoms in the ground state. The first measurement of the quantum state distribution of antihydrogen atoms in a low magnetic field environment of a few mT is described. Furthermore, the data-driven machine learning analysis to identify antihydrogen events is discussed.

C. Amslera, D. Barnab, H. Breukerc, S. Chesnevskayaa, G. Costantinid, M. Fleckc,e, A. Gligorovaa, H. Higakif , E. D. Huntera, M. Horig∗, Y. Kanaih, V. Kletzla, B. Kolbingera, N. Kurodae, A. Lanza, M. Lealid, E. Lodi-Rizzinid, V. Mäckelc, C. Malbrunoti, V. Mascagnaj , Y. Matsudae, D. J. Murtagha, Y. Nagatak, A. Nandaa, L. Nowaki, N. Ogawag,l, W. Pirklg, M. C. Simona, M. Tajimah, Y. Tanakam, S. Ulmerc, U. Uggerhøjn, L. Venturellid, E. Widmanna∗, A. Weisera, T. Wolzi, Y. Yamazakic, J. Zmeskala

The prospects of tests of CPT symmetry using precision spectroscopy of antihydrogen are discussed with special emphasis on the ground-state hyperfine structure, a measurement of which is the aim of the ASACUSA collaboration at the AD/ELENA facility of CERN. Ongoing parallel experiments using hyperfine spectroscopy of hydrogen and deuterium aiming at studying Lorentz invariance by determining coefficients of the Standard Model Extension framework are described.

The ASACUSA collaboration aims at measuring the ground state hyperfine splitting of antihydrogen for probing fundamental symmetries. A cryogenic trap for mixing antiprotons and positrons serves as an antihydrogen source for in-flight spectroscopy. In order to be able to monitor the antihydrogen formation process, a dedicated Micromegas tracking detector has been designed and built to record the annihilation distribution in the trap. In this paper, we present the first results from antiproton annihilation data recorded with the Micromegas, together with a description of the event reconstruction algorithm.

The ASACUSA Collaboration at CERNs Antiproton Decelerator aims to measure the ground state hyperfine splitting of antihydrogen with high precision to test the fundamental symmetry of CPT (combination of charge conjugation, parity transformation, and time reversal). For this purpose an antihydrogen detector has been developed. Its task is to count the arriving antihydrogen atoms and therefore distinguish backgroundevents (mainly cosmics) from antiproton annihilations originating from antihydrogen atoms which are produced only in small amounts. A central BGO crystal disk with position sensitive read-out detects the annihilation and a surrounding two-layered hodoscope is used for tracking charged secondaries. The hodoscope has been recently upgraded to allow precise vertex reconstruction. A machine learning analysis based on measured antiproton annihilations and cosmic rays has been developed to identify antihydrogen events.

Received 2 February 2012DOI:https://doi.org/10.1103/PhysRevLett.108.079902© 2012 American Physical Society

Fluorescence of iron ions induced by an X-ray laser allows the relative oscillator strength for Fe xvii emission to be determined; it is found to differ by 3.6σ from the best quantum mechanical calculations, suggesting that the poor agreement between prediction and observations of the brightest Fe xvii line is rooted in the quality of the underlying atomic wavefunctions used in the models. The interpretation of some of the spectral data from the Chandra and XMM-Newton orbiting X-ray missions has been complicated by discrepancies between theory and observation involving the emission lines from the highly charged Fe16+ ion, also known as Fe XVII. Specifically, the intensity of the strongest Fe XVII line, one of the brightest X-ray emissions from galaxies and stars, is generally weaker than predicted. Sven Bernitt et al. report the results of laboratory experiments in which a target of iron ions was fluoresced with femtosecond X-ray pulses from a free-electron laser. They find a relative oscillator strength that differs by 3.6σ from the best quantum mechanical calculations, suggesting that the poor agreement is rooted in the calculations of the underlying atomic dynamics and that the current astrophysical models are not at fault. Highly charged iron (Fe16+, here referred to as Fe xvii) produces some of the brightest X-ray emission lines from hot astrophysical objects1, including galaxy clusters and stellar coronae, and it dominates the emission of the Sun at wavelengths near 15 ångströms. The Fe xvii spectrum is, however, poorly fitted by even the best astrophysical models. A particular problem has been that the intensity of the strongest Fe xvii line is generally weaker than predicted2,3. This has affected the interpretation of observations by the Chandra and XMM-Newton orbiting X-ray missions1, fuelling a continuing controversy over whether this discrepancy is caused by incomplete modelling of the plasma environment in these objects or by shortcomings in the treatment of the underlying atomic physics. Here we report the results of an experiment in which a target of iron ions was induced to fluoresce by subjecting it to femtosecond X-ray pulses from a free-electron laser4; our aim was to isolate a key aspect of the quantum mechanical description of the line emission. Surprisingly, we find a relative oscillator strength that is unexpectedly low, differing by 3.6σ from the best quantum mechanical calculations. Our measurements suggest that the poor agreement is rooted in the quality of the underlying atomic wavefunctions rather than in insufficient modelling of collisional processes.

In dieser Arbeit wurde zum ersten Mal ein verbotener Ubergang in hochgeladenen Ionen, produziert und gespeichert in einer Elektronenstrahl-Ionenfalle (EBIT), mittels resonanter Laseranregung unter direktem Nachweis der Fluoreszenzphotonen untersucht. Der M1 1s22s22p2 2P3/2-2P3/1-Ubergang in borartigem Ar13+ wurde mit einem durchstimmbaren, gepulsten Farbstofflaser angeregt. Die laserinduzierte Fluoreszenz wurde in Abhangigkeit der Laserfrequenz gemessen und somit die Ubergangswellenlange zu 441.25575(17) nm bestimmt. Daruberhinaus wurde die Temperatur der Ionen durch Verdampfungskuhlung erheblich gesenkt, so das ein Auflosungsvermogen von lambda/delta lambda = 15000 erreicht und die Zeemanaufpaltung des Ubergangs im Magnetfelds der EBIT aufgelost werden konnte. Die ermittelten g-Faktoren des 2P1/2- sowie des 2P3/2-Zustands stimmen exzellent mit fruheren Resultaten uberein. Weiterhin ermoglichte der Einsatz der Laserspektroskopie eine erstmalige Untersuchung der Plasmadynamik von Ionen, die uber eine Zeitdauer von mehreren Sekunden magnetisch in einer EBIT gespeichert waren. Die in diesen Untersuchungen erreichte Genauigkeit ist denen der besten Wellenlangenmessungen an hochgeladenen Ionen ebenburtig. Diese neueMethode eroffnet jedoch einen Zugang zu wesentlich genaueren Messungen bis hin zu neuen optischen Frequenzstandards, die auf verbotenen Ubergangen in hochgeladenen Ionen basieren und um Grosenordnungen unempfindlicher gegenuber ausere Felder und Storungen sind als Ubergange in Atomen und niedriggeladenen Ionen.