New perspectives in the charge radii determination for light nuclei

Aula Renzo Leonardi - Villa Tambosi

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Muonic atoms and ions are excellent systems for studying the atomic nucleus due to the mass of the muon (~ 106 MeV) being about 200 times the mass of the electron. This implies that a muon substituting an electron in an atom is about 200 times closer to the nucleus, which makes such systems to be particularly well suited for accurately determining the root-mean-squared (RMS) nuclear charge radius. Historically the best measurements of absolute radii have been obtained via muonic atom X-ray spectroscopy, mostly studying transitions in the 2p-1s manifold.
Fifteen years ago, one of us (RP) helped establish laser spectroscopy of the lightest muonic atoms which produced ten-fold more precise values of the nuclear charge radii (proton, deuteron, helium-3 and 4), when combined with state-of-the-art nucleon and nuclear structure calculations of the nuclear polarizabilities. The polarizability has for a long time been the limiting uncertainty in the determination of charge radii from muonic atoms, and one of us (FH) has contributed to modern precision calculations in this field. Much of this work in both experiment and theory was motivated by two ECT* Workshops on the "Proton Radius Puzzle", which one of us Co-organized in 2012 and 2014.
While laser spectroscopy of Li, Be, … is currently not feasible, novel X-ray detectors developed by one of us (LG) have demonstrated vastly superior energy resolution for the low-energy X-rays emitted when muons are deexciting inside a muonic atom. These metallic magnetic calorimeters (MMCs) have been used last year at PSI to measure X-ray from muonic Li, Be, B with unprecedented accuracy. When combined with novel theory calculations, such measurements will provide the lightest charge radii with up to an order of magnitude higher precision than the current best values.
Ab initio nuclear structure calculations are now available with nucleon-nucleon and three-nucleon interactions derived from chiral effective field theory. The most advanced calculations also include coupling to the continuum and the ability to treat extremely loosely bound nuclei. This treatment of the continuum is crucial for correctly reproducing the structure of both light and exotic nuclei, especially their spatial extension. Measurements of absolute radii may even be used to obtain also other observables, e.g. electric quadrupole strengths and moments. Another key application of absolute radii are Standard Model tests at the precision frontier.

Organizers

  • Franziska Hagelstein (JGU Mainz & PSI Villigen)
  • Loredana Gastaldo (Kirchhoff Institut für Physik, Heidelberg)
  • Nancy Paul (Laboratoire Kastler Brossel, Paris)
  • Randolph Pohl (JGU Mainz)
See complete details and information

Registration

Registration available from 26/05/2025 until 04/07/2025.

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