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High precision tests of QED Measurement of the alpha-particle and helion rms charge radius and the transition energies in highly-charged ions
Publication . Machado, Jorge Felizardo Dias Cunha; Santos, José; Indelicato, Paul
This work aims to provide insight on Bound-State Quantum-Electrodynamics
(BSQED) by experimental fundamentals high-precision tests in exotic states of
matter. Although BSQED and the relativistic many-body problem have been undergoing
important progress, there are still some issues that require the increase
of the number and accuracy of experimental fundamental tests.
The first part of this work was done within the framework of the recent experiment
in muonic helium ions ( 4He+ and 3He+) by the CREMA collaboration.
This experiment, aims to provide new accurate values for the root-mean-square
(rms) charge radii of the helium isotopes nuclei that are extracted from the measurement of the Lamb Shift, i.e., the measurement of the energy difference between the 2S 2P states. With the goal of measuring the transition energies with an accuracy of at least 50 ppm, the rms charge radii of the helium isotopes will be determined with an uncertainty of 0.03%, a factor of ten more precise than previous
results obtained from electron scattering.
The second part of this work aims the high-precision measurement of x-ray
transitions in Highly-Charged Ions (HCI) using a Double-Crystal Spectrometer
(DCS). These ions were produced in the plasma of an Electron-Cyclotron Resonance
Ion Source (ECRIS). This kind of spectrometer is able not only to provide
high-precision measurements but also reference-free measurements, without reference
to any theoretical or experimental energy. Four transitions energies from
n = 2!n = 1 have been measured in an argon plasma in three different charge
states, He-, Be- and Li-like, with an accuracy of better than 3 ppm. Besides the energies, the natural width of each transition has also been experimentally obtained.
The obtained results are in excellent agreement with the most recent theoretical
calculations.
Measuring the α-particle charge radius with muonic helium-4 ions
Publication . Krauth, Julian J.; Schuhmann, Karsten; Ahmed, Marwan Abdou; Amaro, Fernando D.; Amaro, Pedro; Biraben, François; Chen, Tzu Ling; Covita, Daniel S.; Dax, Andreas J.; Diepold, Marc; Fernandes, Luis M. P.; Franke, Beatrice; Galtier, Sandrine; Gouvea, Andrea L.; Götzfried, Johannes; Graf, Thomas; Hänsch, Theodor W.; Hartmann, Jens; Hildebrandt, Malte; Indelicato, Paul; Julien, Lucile; Kirch, Klaus; Knecht, Andreas; Liu, Yi Wei; Machado, Jorge; Monteiro, Cristina M. B.; Mulhauser, Françoise; Naar, Boris; Nebel, Tobias; Nez, François; dos Santos, Joaquim M. F.; Santos, José Paulo; Szabo, Csilla I.; Taqqu, David; Veloso, João F. C. A.; Vogelsang, Jan; Voss, Andreas; Weichelt, Birgit; Pohl, Randolf; Antognini, Aldo; Kottmann, Franz; DF – Departamento de Física; LIBPhys-UNL; Nature Publishing Group
The energy levels of hydrogen-like atomic systems can be calculated with great precision. Starting from their quantum mechanical solution, they have been refined over the years to include the electron spin, the relativistic and quantum field effects, and tiny energy shifts related to the complex structure of the nucleus. These energy shifts caused by the nuclear structure are vastly magnified in hydrogen-like systems formed by a negative muon and a nucleus, so spectroscopy of these muonic ions can be used to investigate the nuclear structure with high precision. Here we present the measurement of two 2S–2P transitions in the muonic helium-4 ion that yields a precise determination of the root-mean-square charge radius of the α particle of 1.67824(83) femtometres. This determination from atomic spectroscopy is in excellent agreement with the value from electron scattering1, but a factor of 4.8 more precise, providing a benchmark for few-nucleon theories, lattice quantum chromodynamics and electron scattering. This agreement also constrains several beyond-standard-model theories proposed to explain the proton-radius puzzle2–5, in line with recent determinations of the proton charge radius6–9, and establishes spectroscopy of light muonic atoms and ions as a precise tool for studies of nuclear properties.
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Fundação para a Ciência e a Tecnologia
Programa de financiamento
3599-PPCDT
Número da atribuição
PTDC/FIS/117606/2010