Measuring the α-particle charge radius with muonic helium-4 ions

Julian J. Krauth*, Karsten Schuhmann, Marwan Abdou Ahmed, Fernando D. Amaro, Pedro Amaro, François Biraben, Tzu Ling Chen, Daniel S. Covita, Andreas J. Dax, Marc Diepold, Luis M.P. Fernandes, Beatrice Franke, Sandrine Galtier, Andrea L. Gouvea, Johannes Götzfried, Thomas Graf, Theodor W. Hänsch, Jens Hartmann, Malte Hildebrandt, Paul IndelicatoLucile Julien, Klaus Kirch, Andreas Knecht, Yi Wei Liu, Jorge Machado, Cristina M.B. Monteiro, Françoise Mulhauser, Boris Naar, Tobias Nebel, François Nez, Joaquim M.F. dos Santos, José Paulo Santos, Csilla I. Szabo, David Taqqu, João F.C.A. Veloso, Jan Vogelsang, Andreas Voss, Birgit Weichelt, Randolf Pohl, Aldo Antognini, Franz Kottmann

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

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.

Original languageEnglish
Pages (from-to)527-531
Number of pages5
JournalNature
Volume589
Issue number7843
Early online date27 Jan 2021
DOIs
Publication statusPublished - 28 Jan 2021

Bibliographical note

Funding Information:
Acknowledgements This work was performed at HIPA at PSI. We thank the accelerator and beamline support groups for excellent conditions. We also thank L. Simons, U. Röser, M. Nüssli, H. v. Gunten, B. Zehr, W. Lustermann, A. Gendotti, A. Müller, F. Barchetti, B. van den Brandt, P. Schurter, M. Horisberger, A. Weber, S. Spielmann-Jäggi, U. Greuter, P.-R. Kettle, S. Ritt, W. Simons, K. Linner, H. Brückner, K. S. E. Eikema and the PSI, ETH and MPQ workshops and support groups for their help. We acknowledge the support of the following grants: European Research Council (ERC) through StG. 279765 and CoG. 725039, Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Initiative EXC 1098 PRISMA (194673446) and Excellence Strategy EXC PRISMA+ (390831469), EU Horizon 2020 innovation programme STRONG-2020 (grant agreement number 824093), DFG_GR_3172/9–1, MOST of Taiwan under contract number 106-2112-M-007 -021 -MY3, Fundação para a Ciência e a Tecnologia (FCT), Portugal, and FEDER through COMPETE in the framework of project numbers PTDC/FIS-NUC/0843/2012, PTDC/FIS-NUC/1534/2014, PTDC/ FIS-AQM/29611/2017, PEstOE/FIS/UI0303/2011, PTDC/FIS/117606/2010 and UID/04559/2020 (LIBPhys), contract numbers SFRH/BPD/92329/2013, SFRH/BD/52332/2013, SFRH/ BD/66731/2009 and SFRH/BPD/76842/2011, and by SNF 200021L_138175, SNF 200020_159755 and SNF 200021_165854, as well as the ETH-FAST initiative as part of the NCCR MUST programme.

Publisher Copyright:
© 2021, Springer Nature Limited part of Springer Nature.

Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

Funding

Acknowledgements This work was performed at HIPA at PSI. We thank the accelerator and beamline support groups for excellent conditions. We also thank L. Simons, U. Röser, M. Nüssli, H. v. Gunten, B. Zehr, W. Lustermann, A. Gendotti, A. Müller, F. Barchetti, B. van den Brandt, P. Schurter, M. Horisberger, A. Weber, S. Spielmann-Jäggi, U. Greuter, P.-R. Kettle, S. Ritt, W. Simons, K. Linner, H. Brückner, K. S. E. Eikema and the PSI, ETH and MPQ workshops and support groups for their help. We acknowledge the support of the following grants: European Research Council (ERC) through StG. 279765 and CoG. 725039, Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Initiative EXC 1098 PRISMA (194673446) and Excellence Strategy EXC PRISMA+ (390831469), EU Horizon 2020 innovation programme STRONG-2020 (grant agreement number 824093), DFG_GR_3172/9–1, MOST of Taiwan under contract number 106-2112-M-007 -021 -MY3, Fundação para a Ciência e a Tecnologia (FCT), Portugal, and FEDER through COMPETE in the framework of project numbers PTDC/FIS-NUC/0843/2012, PTDC/FIS-NUC/1534/2014, PTDC/ FIS-AQM/29611/2017, PEstOE/FIS/UI0303/2011, PTDC/FIS/117606/2010 and UID/04559/2020 (LIBPhys), contract numbers SFRH/BPD/92329/2013, SFRH/BD/52332/2013, SFRH/ BD/66731/2009 and SFRH/BPD/76842/2011, and by SNF 200021L_138175, SNF 200020_159755 and SNF 200021_165854, as well as the ETH-FAST initiative as part of the NCCR MUST programme.

FundersFunder number
MOST of Taiwan106-2112-M-007 -021 -MY3
NCCR MUST
Horizon 2020 Framework Programme279765, DFG_GR_3172/9–1, 824093, 725039
Seventh Framework Programme
European Research Council
Deutsche Forschungsgemeinschaft194673446, 390831469
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung200020_159755, 200021_165854, 200021L_138175
Fundação para a Ciência e a Tecnologia
Instituto Nacional de Ciência e Tecnologia para Excitotoxicidade e Neuroproteção
European Regional Development Fund
Programa Operacional Temático Factores de CompetitividadePTDC/ FIS-AQM/29611/2017, UID/04559/2020, SFRH/BD/52332/2013, SFRH/BPD/76842/2011, PTDC/FIS/117606/2010, PEstOE/FIS/UI0303/2011, SFRH/ BD/66731/2009, PTDC/FIS-NUC/0843/2012, SFRH/BPD/92329/2013, PTDC/FIS-NUC/1534/2014

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