News Archive 2023

Quantum electrodynamics (QED) is part of the Standard Model of particle physics, which has the ambitious goal of describing all physical effects with the exception of gravity. Tests of the Standard Model are of interest to find clues as to why some predictions do not match experimental observations.
The strength of the magnetic moment of a single electron bound to the nucleus of an atom is determined by the so-called g-factor. The comparison of the experimental g-factor and the g-factor calculated from QED models allows to test current QED models with very high accuracy.

In a recent article published in "Physical Review Letters" members of our division report on the measurements of individual bound electron g-factors of ²⁰Ne⁹⁺ and ²²Ne⁹⁺. The g-factor experiments were performed using the cryogenic Penning-trap setups ALPHATRAP and PENTATRAP at MPIK Heidelberg. In order to determine the g-factor, the nuclear mass of neon and the Larmor frequency (precession frequency of the spin of the stored neon ion in the magnetic field) are required. The Larmor frequency was determined in the ALPHATRAP experiment. The nuclear mass of ²⁰Ne was determined by the PENTATRAP experiment with a precision of 5·10^–12. This is a world record for mass measurements in atomic mass units. Using the nuclear mass and the Larmor frequency, the g-factor of the bound electron in ²⁰Ne⁹⁺ and ²²Ne⁹⁺ was determined with a relative precision of 10^–10.
The comparison of the experimental g-factor and the g-factor calculated from QED models shows an agreement to ten decimal places and provides the most precise test of the theory of self-interaction of the bound electron.

Please read more in the article ... >

Further information also in the press release of the MPIK 

Modern atomic clocks are among the most accurate measurement tools. They are the basis of advanced technology like the GPS system. The invention of the frequency comb opened the path to atomic clocks using optical transitions in trapped, single, highly charged ions (HCI).
In a recent article published in "Physical Review Letters" members of our division report on the identification of a metastable electronic state in highly charged lead ions (Nb-like ²⁰⁸Pb⁴¹⁺) which could be used as a clock state. The Penning-trap mass spectrometer PENTATRAP was used to directly determine the excitation energy of the metastable state in Pb⁴¹⁺ ions to be 31.2(8) eV. With a fractional mass uncertainty of 4·10^–12 this is one of the most precise mass measurements to date.
The experimental work was combined with a theoretical work from the division of Christoph Keitel at MPIK and Paul Indelicato from the Sorbonne University, in which the transition energy was theoretically determined with two extensive, partially different ab initio multi-configuration Dirac-Hartree-Fock calculations.

Please read more in the article ... >

Further information also in the press release of the MPIK 

The Cabibbo-Kobayashi-Maskawa (CKM) matrix is a central cornerstone in the formulation of the Standard Model of particle physics. For the Standard Model to be complete, the CKM matrix must be unitary. The first element in the top row of the matrix, V_ud, can be extracted from measurements of beta-decay rates, considering theoretical corrections such as the nuclear charge distribution (nuclear charge radius).
In ^26mAl, those corrections are very small and it has one of the most precisely measured beta-decay rates that constrains the V_ud value. Thus, ^26mAl is of particular importance for the determination of V_ud.

In a recent article published in "Physical Review Letters", P. Plattner et al. report on the first experimental determination of the nuclear charge radius of ^26mAl by collinear laser spectroscopy. For this purpose, two independent experiments were performed. One at the COLLAPS beamline at ISOLDE-CERN and the other at the IGISOL CLS beamline in Jyväskylä, Finland. The new precise charge radius value R_c=3.130(15) fm of ^26mAl directly affects the determination of V_ud and thus the testing of CKM-matrix unitarity.

Please read more in the article ... >

Further information also in the press release of CERN 

The article has been selected for a Viewpoint in Physics. Please read also the viewpoint on the article  by T. E. Cocolios (KU Leuven).

The article has also been selected as "Editor's Suggestion". This is an award "based on the potential interest in the results presented and, importantly, on the success of the paper in communicating its message, in particular to readers from other fields" (see also here )

The neutron-deficient exotic nuclei of mercury and bismuth alternate from spherical (football/soccer) to deformed (rugby ball) shapes as single neutrons are removed from the nucleus. This phenomenon is called shape shifting. It was first discovered a little more than 50 years ago in the light mercury nuclei at the ISOLDE facility (CERN), Geneva.

In a recent article published in "Physical Review Letters", J. G. Cubiss et al. report on the changes in mean-squared charge radii of neutron-deficient gold nuclei that have been determined using the in-source, resonance-ionization laser spectroscopy technique at ISOLDE. The new experimental data reveal that neutron-deficient gold nuclei also display shape shifting.

Please read more in the article ... >

Further information also in the press release of CERN 

Scientists from our division and other institutions have obtained a significantly higher ionization rate in dilute molecular clouds than previously inferred. For their observations, the scientists verified the chemical destruction pathways of the OH⁺ molecule in the worldwide unique cryogenic ion storage ring CSR at the MPIK in Heidelberg, Germany.

Please read more in the article ... >

Further information also in the press release of the MPIK 

Quantum electrodynamics is the best-tested theory in physics. It describes all electrical and magnetic interactions of light and matter. Scientists of our division have now used precision measurements on their ALPHATRAP experiment to investigate the magnetic properties of electrons bound to highly ionized tin atoms. Such tests provide insights into the behavior of particles under extreme field strengths. They also serve as a starting point for the search for new physics.

Please read more in the "Nature" article ... >

Further information also in the press release of the MPIK 

Experimental observables of simple atomic systems with a single or few electrons, such as atomic and molecular hydrogen, helium, and their ions, enable extremely precise tests of the standard model of physics. The properties of the fundamental particles, such as the mass of the electron and the mass and charge radius of the light nuclei, are thus of importance for fundamental physics.
The LIONTRAP (Light ION TRAP) experiment, situated at Johannes Gutenberg University (JGU) in Mainz, Germany, is a dedicated high-precision Penning-trap mass spectrometer aiming for most precise mass measurements on various light ions.

In a recent article published in "Physical Review Letters", S. Sasidharan et al. report on a 12 parts-per-trillion measurement of the mass of a ⁴He²⁺ ion using LIONTRAP. From the ion mass m(⁴He²⁺), the atomic mass of the neutral atom was determined without loss of precision: m(⁴He) = 4.002 603 254 653(48) u.
This result is slightly more precise than the current CODATA18 literature value but deviates by 6.6 standard deviations.
To further investigate the inconsistencies in the light ion mass regime, a re-measurement of the ³He/¹²C mass ratio using LIONTRAP is planned.

Please read more in the article ... >

Further information also in the press releases of the MPIK  and the GSI Helmholtz Centre for Heavy Ion Research Darmstadt 

In a recent article published in "Physical Review Letters", L. Nies et al. report on measurements of the isomeric excitation energies in neutron-deficient indium isotopes. The experiment was performed using the ISOLTRAP  multireflection time-of-flight mass spectrometer (MR-TOF MS) at ISOLDE /CERN, Geneva. The high precision measurements exploited a major improvement in the resolution of the ISOLTRAP MR-TOF MS. This allowed to measure the excitation energy (671(37) keV) of the 1/2⁻ isomer in ⁹⁹In at N=50 for the first time.
The systematics of the isomer excitation energy now reach the crucial N=50 shell closure, confirming its constancy, even when all neutrons are removed from the valence shell.

Advances in modern nuclear models are not only of interest for nuclear shell structure investigations but are also frequently used in metrology, atomic physics, and quantum chemistry.
The improved experimental results were compared to state-of-the-art large-scale shell model (LSSM) and density functional theory (DFT) calculations, as well as to ab initio calculations using the valence-space in-medium similarity renormalization group (VS-ISMRG) and the CCSM method. The models have difficulties describing both the isomer excitation energies and ground-state electromagnetic moments along the indium chain.

Please read more in the article ... >

Further information also in the press release of CERN .

In a recent article published in "Physical Review Letters", M. Wang et al. report on high-precision mass measurements of upper fp-shell N=Z−2 and N=Z−1 nuclei. The experiment was performed at the Heavy Ion Research Facility in Lanzhou (HIRFL)  (China). Using a novel method of isochronous mass spectrometry, the masses of ⁶²Ge, ⁶⁴As, ⁶⁶Se, and ⁷⁰Kr were measured for the first time, and the masses of ⁵⁸Zn, ⁶¹Ga, ⁶³Ge, ⁶⁵As, ⁶⁷Se, ⁷¹Kr, and ⁷⁵Sr were redetermined with improved accuracy.

The new masses allowed to derive residual proton-neutron interactions (δV_pn) in the N=Z nuclei, which are found to decrease (increase) with increasing mass A for even-even (odd-odd) nuclei beyond Z=28. This observed bifurcation of δV_pn could not be reproduced by available mass models.
Ab initio calculations using the chiral nuclear force with three-nucleon interaction included could reproduce the bifurcation. However, for odd-odd N=Z nuclei δV_pn is systematically overestimated. This implies that state-of-the-art ab initio approaches need further improvement, and accurate masses of nuclei along N=Z provide an important testing ground.

Please read more in the article ... >

New nuclear physics data provide a better understanding of the properties of neutron stars. High-precision measurements of nuclear masses reveal germanium-64 as a waiting-point nucleus in nucleosynthesis via fast proton capture and form the basis for modelling X-ray bursts on neutron stars as part of binary systems.

The experiments performed by the Storage Ring Nuclear Physics Group  at the Heavy Ion Research Facility in Lanzhou (HIRFL)  (China) as well as the interpretation of the data were supported by researchers from our "Stored and Cooled Ions" division at the MPIK in Heidelberg and the ASTRUm group  at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt within a cooperation successfully ongoing for more than 10 years.

Please read more in the "Nature Physics" article .

Further information also in the press release of the MPIK .