Precision experiments with stored ions and antimatterMax Planck Institute for Nuclear PhysicsUniversity of HeidelbergEuropean Research Council
Ultracold Ions and Antimatter Research
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Welcome to new Ph.D. student Christian Zimmer

As of July 2016 a new Ph.D. student has joined our group. Christian Zimmer will be working at CERN full-time. His main project will be the demonstration of laser cooling of molecular anions. He will be part of the AEGIS-Borealis team at CERN headed by Sebastian Gerber.
Update: Christian has been honored as the 100th student to receive a Gentner stipend funded by the German Federal Ministry of Education and Research (BMBF). The stipend is awarded to students with an excellent academic record at the B.Sc. and M.Sc. level.

Christian Zimmer
Photo credit: CERN


First anions trapped in Penning trap

The trapping of anions in a Penning trap and their pre-cooling with electrons is an important milestone towards the demonstration of laser cooling of La-. Now the trapping of gold anions in our Penning trap has been achieved for the first time. The image shows the ions captured in the Penning trap, then ejected downstream onto a micro-channel plate detector with a phosphor screen. The cross indicates the center of the screen, the circle (radius in mm) provides a scale.

Trapped ions
MCP image of Au anions captured in a Penning trap


Successful completion of doctoral exam for Elena Jordan

Elena Jordan today passed her Ph.D. exam with straight "1.0" marks. Congratulations! From December on she will remain part of the group as a post-doc.

Doctoral exam Elena
Elena in front of the black board notes of her doctoral exam

Reference to thesis: E. Jordan, “High-resolution Doppler laser spectroscopy of the laser cooling candidate La-,” Ph.D. thesis, University of Heidelberg (2015).

Article on La- spectroscopy published

An article in which we describe recent spectroscopic results on La- has just been published. The measurements show that the potential laser cooling transition in this anion, which had been theoretically predicted and experimentally observed in a rough survey, does indeed exist. We were able to partially resolve the hyperfine structure, which is due to the non-vanishing nuclear spin of the only stable isotope of lanthanum. The observed spectra reveal that La- can be laser-cooled with only three laser frequencies slightly detuned with respect to each other. In the medium term, the technique will be used to create colder antihydrogen for precision antimatter experiments at CERN.

Hyperfine spectrum of La<sup>-</sup>
Absorption spectrum of the potential laser cooling transition in La- with resolved hyperfine structure

Reference: E. Jordan et al., “High-resolution spectroscopy on the laser-cooling candidate La-,” Phys. Rev. Lett. 115 (2015) 113001.

Review article on antimatter physics

A review article by Alban Kellerbauer on antimatter physics has appeared in European Review. The paper is based on a plenary lecture given at the 25th Annual Conference of the Academia Europaea in Wroclaw, Poland. Among the other distinguished speakers were Sir Martin Rees, Astronomer Royal and Sir Tom Kibble, co-discoverer of the Higgs mechanism. Their papers were published in the same issue of European Review.

Reference: A. Kellerbauer, “Why antimatter matters,” European Review 23 (2015) 45.

Article on measurement of the Zeeman effect in Os-

Our measurements of the Zeeman effect in Os- have been published. These experimental results are a prerequisite for the planned laser cooling of atomic anions. This is the first time the Zeeman effect has been observed in the bound-bound transition of an atomic anion. The measured Landé g factors agree very well with the calculated values. In the article, the prospects for laser cooling Os- are summarized.

Zeeman absorption spectra
Measured absorption spectra of Os- in an external magnetic field (sigma transitions)

Reference: A. Kellerbauer et al., “Measurement of the Zeeman effect in an atomic anion: Prospects for laser cooling of Os-,” Phys. Rev. A 89 (2014) 043430.

Review article on antimatter physics appeared (in German)

A review article by Alban Kellerbauer on the history of antimatter in the laboratory has appeared in Physik-Journal, the official journal of the German Physical Society. The article rehashes the history of antimatter, from its discovery in 1933 to the most recent experiments at CERN.

Reconstructed antihydrogen annihilation event
Artist's conception of an antihydrogen annihilation event, as reconstructed with the ATHENA detector

Reference: A. Kellerbauer, “Antimaterie im Labor,” Physik-Journal 13-7 (2014) 27.

Anke Heilmann completes La- source project

Today Anke handed in her B.Sc. thesis. Her thesis project dealt with the production of a beam of lanthanum anions for the UNIC project. Previous work had shown that it is difficult to produce a stable beam of negative ions of the lanthanide elements with a cesium sputter ion source because the ionizer tends to be poisened by some of the produced anions. Anke managed to obtain an La- beam of many nA for as long as a week thanks to a clever target design and carefully chosen source operating conditions.

Reference: A. Heilmann, “Production and characterization of a mass-separated lanthanum anion beam,” B.Sc. thesis, University of Heidelberg (2012).

Review article on current status of CERN antimatter experiments published (in German)

A review article by Alban Kellerbauer was published in the July 2012 issue of German popular-science magazine "Physik in unserer Zeit." The article rehashes the development of antimatter physics from the 1930s until today and details the present status of the four antihydrogen experiments currently taking data or being set up at CERN's Antiproton Decelerator.

Alpha magnetic spectrometer
Alpha magnetic spectrometer (Photo credit: NASA)

Reference: A. Kellerbauer, “Das Antimaterie-Rätsel,” Phys. Unserer Zeit 43 (2012) 174.

Radio program on antimatter with statements by Alban Kellerbauer (in German)

A radio program by Armin Stadler on antimatter science and fiction was broadcast today on Austrian radio channel ORF Ö1. It includes material from an interview with Alban Kellerbauer recorded in April. Other participating scientists were Eberhard Widmann (Stefan Meyer Institute, Vienna), Christoph Schwanda (Institute for High-Energy Physics, Vienna) and Piergiorgio Picozza (University of Rome "Tor Vergata").

MP3 stream 24:38 min (Copyright ORF 2012)

Reference: A. Stadler, “Im Spiegelkabinett der Antimaterie. Rundgang durch eine verkehrte Welt,” ORF Ö1, 2012-05-15 09:05.
Link to program website

ERC Starting Grant for Alban Kellerbauer

Alban Kellerbauer has won a Starting Grant of the European Research Council in the fourth round of calls (StG 2010). The grant with a funding volume of more than 1.1 million euros over five years was awarded for the work on laser cooling of negative ions.
The European Research Council (ERC) was set up in 2006 to support investigator-driven frontier research. Its main aim is to "stimulate scientific excellence by supporting and encouraging the very best, truly creative scientists, scholars and engineers to be adventurous and take risks in their research." The scientists are encouraged to go beyond established frontiers of knowledge and the boundaries of disciplines. The ERC complements other funding activities in Europe such as those of the national research funding agencies, and is a flagship component of the 'Ideas Programme' of the European Union's Seventh Research Framework Programme (FP7).

ERC Logo

Article on Os hyperfine structure spectroscopy published

The laser cooling of negative osmium will require the confinement of a cloud of Os ions in a Penning trap. In the strong magnetic field of the trap, the cooling transition line will split due to the Zeeman effect. The knowledge of the exact Zeeman structure is crucial, because it guides the choice of the sublevel used for cooling and determines whether the transition is closed or whether the excited state may decay to intermediate states, requiring a repumping laser. Since the Zeeman splitting depends on the angular momentum quantum numbers, we have measured the hyperfine structure of the bound–bound transition in two Os isotopes with a non-zero nuclear spin. This has allowed us to determine the previously unknown total angular momentum of the excited state and calculate the Zeeman structure of 192Os.

Calculated energy level diagram of <sup>192</sup>Os<sup>−</sup> in an external magnetic field
Calculated energy level diagram of 192Os in an external magnetic field

Reference: A. Fischer et al., “First optical hyperfine structure measurement in an atomic anion,” Phys. Rev. Lett. 104 (2010) 073004.

Arne Fischer's graduate thesis submitted

With only one more exam to go, Arne Fischer is fast approaching the end of his graduate studies and the award of his Diplom degree. He today submitted his graduate thesis on the spectroscopy of the osmium anion, a major contribution to the first experimental results and the paper in which they are presented (see the previous News item). In his thesis, Arne details the design and construction of the collinear spectroscopy setup and his development of an electric-field detacher, with which the sensitivity of the apparatus was increased by about two orders of magnitude.

Reference: A. Fischer, “Laser spectroscopy on the negative osmium ion,” Diplom thesis, University of Heidelberg (2009).

Article on Os spectroscopy published

With the long-term goal of laser cooling a negative ion for the first time, we have thoroughly investigated the only known electric-dipole transition in an atomic anion by collinear laser spectroscopy. A publication on the first results, concerning the transition frequency and resonant cross-section, has just appeared in Physical Review Letters. Using a unique combination of laser excitation and electric-field neutralization, we have improved the previous transition frequency measurement by more than a factor 100. Our value for the Einstein A coefficient is lower than previously found, suggesting that pre-cooling of Os to liquid-helium temperature may be required in order to achieve reasonable laser cooling times of a few minutes.

Energy level diagram for Os<sup>−</sup>
Energy level diagram for Os

Reference: U. Warring et al., “High-resolution laser spectroscopy on the negative osmium ion,” Phys. Rev. Lett. 102 (2007) 043001.

Alban Kellerbauer completes habilitation

Based on his habilitation thesis submitted in October 2008 and on his graduate-level teaching at the University of Heidelberg, the Faculty of Physics and Astronomy today awarded Alban Kellerbauer the degree of Privatdozent. The habilitation is the highest academic qualification awarded in Germany and attests the bearer's suitability for a senior faculty position at a university. The cumulative thesis is centered around 8 research papers concerned with the results of the antimatter experiment ATHENA and the spectroscopy of osmium anions whose aim is the production of ultracold antihydrogen for future precision experiments. An article on the subject of the public lecture has since appeared in the January 2010 issue of German popular-science magazine "Physik in unserer Zeit."

Alban Kellerbauer during his public lecture on Lippmann photography
Alban Kellerbauer during his public lecture on Lippmann photography

A. Kellerbauer, “Dynamics of antihydrogen production in Penning traps and indirect laser cooling of antiprotons,” Habilitation thesis, University of Heidelberg (2008).
A. Kellerbauer, “Interferentielle Fotografie – Farbbilder aus gefrorenem Licht,” Phys. Unserer Zeit 41 (2010) 16.

AEGIS experiment approved

The CERN Research Board has approved our proposal for the AEGIS experiment (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) and committed itself to an extension of the operation of the Antiproton Decelerator (AD) facility until 2016. AEGIS will test the gravitational interaction of antimatter using an antihydrogen beam. The AEGIS proposal had already been positively evaluated by the scientific committee in January 2008, but the final go-ahead depended on CERN's continued support for the AD, where AEGIS will be installed. Construction of the AEGIS apparatus will begin in late 2009 or early 2010.

Overview sketch of the AEGIS experiment
Overview sketch of the AEGIS experiment

Reference: A. Kellerbauer et al., “Proposed antimatter gravity measurement with an antihydrogen beam,” Nucl. Intrum. Methods B 266 (2008) 351.

Raoul Heyne graduates

Fulfilling the final requirement for the completion of his Diplom degree at the University of Heidelberg, Raoul Heyne today handed in his graduate thesis. The subject of his thesis work was the creation, diagnostics and manipulation of an electron plasma. Cold electrons will in the future be used to pre-cool osmium anions prior to in-trap spectroscopy. In close collaboration with post-doc Carlo Canali, Raoul managed to confine several million electrons in the Penning trap and monitor their properties with a sophisticated plasma diagnostics device originally developed at the INFN Genoa. The thesis (in English) is available for download in PDF format.

Reference: R. Heyne, “Creation, diagnostics and manipulation of a non-neutral one-component plasma”. Diplom thesis, University of Heidelberg (2008).

Hyperfine structure in Os

Following our first laser spectroscopy studies on the negative ion of the most abundant osmium isotope 192Os, we have repeated the same measurements on all naturally occurring isotopes, including 184Os with a natural abundance of only 0.02%. The isotopes with A = 187 and A = 189 have a non-vanishing nuclear spin, which leads to a hyperfine splitting of the transition line. This is the first time a hyperfine splitting in a negative ion has ever been recorded by optical spectroscopy.

Observed hyperfine structure in the negative <sup>187</sup>Os<sup>–</sup> ion
Observed hyperfine structure in the negative 187Os ion.

Time-controlled production of antihydrogen

An article describing a technique for rapidly turning antihydrogen production ON and OFF has just appeared. Under normal operating conditions in the ATHENA mixing trap, antihydrogen is created some 20–30 ms after antiprotons and positrons are brought into overlap. We have now shown that the process can be interrupted quickly by heating the positron plasma with a radiofrequency signal. Once the heating is turned off, antihydrogen production resumes with a rise time of about 1 s. In addition to providing a pulsed source of antihydrogen, this technique also allowed a more detailed determination of the temperature dependence of antihydrogen production than had previously been achieved.

Space and time evolution of antiproton annihilations following antihydrogen production
The technique allows a fine control over antihydrogen production, as illustrated by the space and time evolution of antiproton annihilations.

Reference: M. Fujiwara et al., “Temporally controlled modulation of antihydrogen production and the temperature scaling of antiproton-positron recombination,” Phys. Rev. Lett. 101 (2007) 053401.

First successful spectroscopy on negative osmium ions

Roughly two years after the start of the Os- spectroscopy project, we have observed the first resonance of the bound excited state in the negative osmium ion. This frequency measurement is an essential milestone on the way to laser cooling of negative ions. The spectra are acquired by collinear laser spectroscopy using a mass-separated beam of 192Os- at beam energies ranging from roughly 3.75 to 6.5 kV. The width of the resonance is dominated by the energy spread of the beam and varies between 40 and 75 MHz. Data analysis is still in progress, but we expect a final uncertainty of the transition frequency of about 40 MHz, roughly two orders of magnitude more precise than the previous measurement.

Resonance of negative Os ion
One of the first resonances of the bound excited state in the negative osmium ion observed with our apparatus.

Penning trap completed and installed

The construction of the cylindrical Penning trap for the project “High-resolution spectroscopy on the osmium anion” has been completed. The trap consists of 11 trap electrodes as well as two high-voltage electrodes for the capture of the 5-keV negative osmium ions. Each electrode is connected to the electrical feedthroughs by two independent wires to ensure fail-safe operation. After a thorough check of all electrical connections, the trap was inserted into the bore of our superconducting magnet and the chambers were evacuated. The barium oxide electron source, which will supply the electrons for the pre-cooling of the negative ions, was also installed. After some days of pumping, the magnet will be cooled down and turned on for the first tests with electron plasmas.

Jan Meier displaying his diploma
Post-doc Carlo Canali puts the finishing touches on the Penning trap prior to installation.

Jan Meier graduates

After his last oral exam last week, graduate student Jan Meier today officially graduated from the University of Heidelberg with a Diplom degree. His thesis project consisted of the design and construction of a negative-ion source based on the time-honored MISS sources employed at the MPI-K accelerator lab. He also designed and built the mass separation stage and the beam line to the Penning trap, including the ion-optical elements required for efficient beam transport. The thesis (in English) is available for download in PDF format.

Jan Meier displaying his diploma
Jan Meier proudly displays his diploma after the graduation ceremony.

Reference: J. Meier, “Matching of the beam from a negative-ion source for capture in a Penning trap”. Diplom thesis, University of Heidelberg (2007).

Superconducting magnet commissioned

An engineer of the magnet manufacturer Cryogenic is visiting the institute this week in order to install and commission the superconducting magnet for the Os- spectroscopy project. The magnet system was successfully ramped to 6 T repeatedly, including also a reversal of the coil's polarity. These successful tests pave the way for the installation of the cylindrical Penning trap, whose construction at the MPI-K's mechanical workshop will begin in January 2008.

Reception of superconducting magnet
Cryogenic engineer David Gillingham discusses the magnet operation with graduate student Raoul Heyne.

Superconducting magnet for Os- spectroscopy project delivered

The superconducting magnet which constitutes the cornerstone of the project “High-resolution spectroscopy on the osmium anion” has been delivered to our lab. The 6-tesla magnet system, made by the British firm Cryogenic, is innovative in several ways: First, it contains no liquid-cryogen reservoirs. Instead, the superconducting coil is cooled by a cryocooler compressor, which operates with a closed cryogen circuit much like a refrigerator. Secondly, the superconducting coil is made from an alloy of nyobium and tin with a higher critical temperature than conventional systems. This will ensure fail-safe operation at the specified magnetic field and act as a contingency in case the nominal heat load to the cooler is exceeded.

Reception of superconducting magnet
Graduate student Ulrich Warring mounts the superconducting magnet on its support.

Review article on antimatter physics published (in German)

A review article by Alban Kellerbauer on antimatter physics has just appeared as the feature of the July 2007 issue of German popular-science magazine "Physik in unserer Zeit." The article explains the motivation for antimatter research as a means for understanding the prevalence of matter in the present Universe. The most important experimental results obtained at the Antimatter Factory at CERN are summarized and an outlook towards future experiments is given.

Graphics from journal titlepage
Are there anti-galaxies in the Universe?

Reference: A. Kellerbauer, Phys. Unserer Zeit 38 (2007) 168.

Laser for Os- spectroscopy project delivered

Employees of the company Xiton Photonics delivered the narrow-band continuous-wave laser which is a central component of the Os- spectroscopy project. The device consists of an optical parametric oscillator (OPO) pumped by a 5-W solid-state laser at 532 nm. It will output about 200 mW at 1162.7 nm and with a bandwidth of less than 5 MHz.

Inspection of cw OPO laser
Post-doc Marco Amoretti inspects the setup of the cw OPO laser.

Ramsey's method of separated oscillatory fields applied to mass measurements

The ISOLTRAP team has applied the Ramsey method of separated oscillatory fields to the excitation of radioactive ions in a Penning trap. This technique allows an improvement in the precision of mass measurements on short-lived nuclides. Alternatively, a mass result of comparable quality can be obtained in about one third the time needed with the traditional excitation envelope. The technique was applied to a mass measurement on 38Ca, a radionuclide with a half-life of only 440 ms, which was determined with a relative precision of about 10-8. 38Ca is a superallowed beta emitter whose mass is important for a test of the conserved-vector-current hypothesis, an important postulate of the Standard Model.

Reference: S. George et al. (ISOLTRAP Collaboration), Phys. Rev. Lett. 98 (2006) 162501.

New evidence for dominant antihydrogen recombination process

In order to shed light on the process responsible for antihydrogen production in a nested Penning trap, radiative recombination was stimulated by shining the light a continuous-wave CO2 laser into the interaction region of the ATHENA experiment. A negligible enhancement of antihydrogen production due to the laser stimulation was observed. This evidence strongly suggests that three-body recombination is the dominant production process.

Reference: M. Amoretti et al. (ATHENA Collaboration), Phys. Rev. Lett. 97 (2006) 213401

ATHENA observes cold protonium

In a reanalysis of 2002 and 2003 data taken at CERN's Antiproton Decelerator, evidence for the production of protonium has been found. Protonium, the quasistable exotic system consisting of a proton and an antiproton, was synthesized following the interaction of antiprotons with residual-gas molecules in the ATHENA Penning trap. A careful analysis of the spatial distribution of antiproton annihilation events allowed a determination of the kinetic energy, quantum states, and lifetime of the produced protonium. The slow protonium may be accessible to laser spectroscopy.

Reference: N. Zurlo et al. (ATHENA Collaboration), Phys. Rev. Lett. 97 (2006) 153401

ISOLTRAP measures the masses of neutron-rich krypton isotopes

The atomic masses of the neutron-rich krypton isotopes 84Kr, 86-95Kr have recently been measured with the tandem Penning trap mass spectrometer ISOLTRAP with unprecedented precision ranging from 2x10-7 to 2x10-8. The short-lived isotopes 94Kr (T1/2 = 210 ms) and 95Kr (T1/2 = 114 ms) were measured for the first time. A significant disagreement with the previous values tabulated in the Atomic-Mass Evaluation was found in the case of 89Kr and 91Kr.

Reference: P. Delahaye et al. (ISOLTRAP Collaboration), Phys. Rev. C 74 (2006) 034331

ATHENA develops new method for cooling and centering ions

Using antiprotons from CERN's Antiproton Decelerator, an extension of the buffer gas cooling technique was successfully demonstrated. Antiprotons were immersed in a dilute electron gas and their radial motions converted by cyclotron excitation. The method will allow a finer control over the collections of antimatter particle used in the production of antihydrogen.

Reference: A. Kellerbauer et al. (ATHENA Collaboration), Phys. Rev. A 73 (2006) 062508