Atomare paritätsverletzung in myonischer Röntgenstrahlung

• Antragsteller: Frederik Wauters, Ph.D.
• Fachliche Zuordnung: Kern- und Elementarteilchenphysik, Quantenmechanik, Relativitätstheorie, Felder
• Förderung: Förderung von 2018 bis 2023
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 392566020

• Erstellungsjahr: 2023

Zusammenfassung der Projektergebnisse

Due to the large mass of the muon relative to the electron, muonic atoms show excellent sensitivity for nuclear finite size effects and short range interactions between the muon and the nucleus. More specifically, the large overlap between the muon wave function and atomic nucleus leads to an enhanced mixing between the opposite parity 2s and 2p atomic states. Therefore, the otherwise pure M1 2s1s transition has a parity non-conserving E1 component, which allow to study parity-odd neutral currents in this system. The goal of this project was to investigate the feasibility of such a measurement. We have measured the single-photon 2s1s transition for the first time in muonic atoms. Previous efforts failed because of the overwhelming Compton background of the circular muonic X-ray transitions. One approach we adopted was to utilize muonic hydrogen to muonic krypton transfer reactions to boost the 2s population. A clear signal was observed with a branching ratio > 10^−4 . The relevant backgrounds were quantified and suppressed where possible. As a second strategy we implemented event tagging techniques in the analysis, selecting events where the muonic X-ray cascade populates the 2s level. A background suppression factor of ten or more was achieved, this however at the cost of a large loss in detection efficiency. With the signal and background yields observed, we can set a limit on the reach of a muonic atomic parity violation experiment with germanium detectors of ca. 10^−4 on the parity odd amplitude. For Z≃30 nuclei this would equate to an order one Standard Model test. These measurements were performed at the Paul Scherrer Institute in Switzerland in the scope of the muX project, which operates a high-purity germanium detector array at a secondary muon beam line. Further measurements in the scope of this project focus on precision charge radii measurements, extending the technique of muonic atom spectroscopy to long-lived radioisotopes. For this purpose we developed a novel technique utilizing a series of transfer reaction in a hydrogen gas cell to stop muons in a microgram target. First successful measurements with curium were performed, we will in the near future continue with radium and potassium isotopes. Since the start of this project, a rich muonic X-ray program has been established at the Paul Scherrer Institute.

Projektbezogene Publikationen (Auswahl)

• “Towards nuclear structure with radioactive muonic atoms.” In: Nuovo Cim. C 42.2-3-3 (2019), p. 125.
  A. Skawran, A. Adamczak, A. Antognini, N. Berger, T. E. Cocolios , R. Dressler, C. Düllmann, R. Eichler, P. Indelicato, K. Jungmann, K. Kirch, A. Knecht, J. J. Krauth, J. Nuber, A. Papa, R. Pohl, M. Pospelov, E. Rapisarda, D. Renisch ... & L. Willman
  
• Measurement of the quadrupole moment of 185Re and 187Re from the hyperfine structure of muonic X rays. Physical Review C, 101(5).
  Antognini, A.; Berger, N.; Cocolios, T. E.; Dressler, R.; Eichler, R.; Eggenberger, A.; Indelicato, P.; Jungmann, K.; Keitel, C. H.; Kirch, K.; Knecht, A.; Michel, N.; Nuber, J.; Oreshkina, N. S.; Ouf, A.; Papa, A.; Pohl, R.; Pospelov, M.; Rapisarda, E. ... & Willmann, L.
  
• The muX project. SciPost Physics Proceedings(5).
  Wauters, Frederik & Knecht, Andreas
  
• “Science Case for the new High-Intensity Muon Beams HIMB at PSI.” In: (Nov. 2021)
  M. Aiba et al
  
• Characterization of a Continuous Muon Source for the Non-Destructive and Depth-Selective Elemental Composition Analysis by Muon Induced X-and Gamma-rays. Applied Sciences, 12(5), 2541.
  Biswas, Sayani; Gerchow, Lars; Luetkens, Hubertus; Prokscha, Thomas; Antognini, Aldo; Berger, Niklaus; Cocolios, Thomas Elias; Dressler, Rugard; Indelicato, Paul; Jungmann, Klaus; Kirch, Klaus; Knecht, Andreas; Papa, Angela; Pohl, Randolf; Pospelov, Maxim; Rapisarda, Elisa; Reiter, Peter; Ritjoho, Narongrit; Roccia, Stephanie ... & Amato, Alex
  
• Muonic X-ray measurmements at PSI with medium and high-Z nuclei. Proceedings of The 22nd International Workshop on Neutrinos from Accelerators — PoS(NuFact2021), 183. Sissa Medialab.
  Wauters, Frederik
  
• Muonic atom spectroscopy with microgram target material. The European Physical Journal A, 59(2).
  Adamczak, A.; Antognini, A.; Berger, N.; Cocolios, T. E.; Deokar, N.; Düllmann, Ch. E.; Eggenberger, A.; Eichler, R.; Heines, M.; Hess, H.; Indelicato, P.; Kirch, K.; Knecht, A.; Krauth, J. J.; Nuber, J.; Ouf, A.; Papa, A.; Pohl, R.; Rapisarda, E. ... & Wauters, F.
  
• “Muonic atoms for fundamental and applied nuclear science.” In: NuPECC LRP2024 Community input (2023).
  Thomas Cocolios & Frederik Wauters, reas Knecht.