Reviewed by Lexie CornerJul 25 2024
In a recent study published in the journal Physical Review Letters, a team of researchers from the University of Bonn has challenged the accuracy of current theoretical models describing helium's transition from its ground to its first excited state. By studying this process through electron scattering, they uncovered a discrepancy between experimental and theoretical results. To address this, a multidisciplinary team has undertaken a fresh calculation of the observed transition.
A photon is absorbed by the ground state of helium-4. This excites the transition to the first excited state of helium-4, which sits just above the energy threshold for separation into a proton and a hydrogen-3 nucleus. Image Credit: Dean Lee
The Science
Examining the reasons behind discrepancies between theoretical calculations and experimental results is a crucial aspect of physics research. An alpha particle, or helium-4 nucleus, was the subject of a recent German experiment. Since helium-4 only has two protons and two neutrons, theoretical calculations can be used to describe it relatively easily. This makes it helpful for accurate nuclear physics testing. The experiment investigated the transition of helium-4 from its ground state to its first excited state using electron scattering. Their findings are in good agreement with those of the recent experiment.
The Impact
The first excited state of the helium-4 nucleus has an energy slightly above the threshold at which the nucleus splits into a proton and a hydrogen-3 nucleus. This state's characteristics highly depend on the narrow gap between its energy and the separation threshold. The new calculations reproduce this energy difference accurately, which may also account for their ability to reproduce the recently obtained experimental data from Germany. The results will aid future theoretical predictions of nuclear structure.
Summary
Utilizing an interaction that replicates the general characteristics of light and medium-mass nuclei, researchers from the University of Bonn (Germany), Forschungszentrum Jülich (Germany), Gaziantep Islam Science and Technology University (Turkey), and the Facility for Rare Isotope Beams at Michigan State University conducted ab initio lattice calculations. The transition from the ground state of 4He to its first excited state, as calculated, agrees well with recent Mainz experimental data.
The accurate reproduction of the difference between the excited state energy and the energy threshold for splitting into a proton and helium-3 nucleus is a fundamental characteristic of the new lattice calculations. Other recent theoretical work has discussed how important it is to reproduce this energy difference accurately. The new findings give confidence that the nuclear force is well understood; however, researchers must carefully consider sensitivities to nearby energy thresholds in future theoretical calculations.
Funding
The Department of Energy's SciDAC-5 NUCLEI Collaboration, the European Research Council, Deutsche Forschungsgemeinschaft, the Chinese Academy of Sciences, and Volkswagen Stiftung all provided financial support for this study. The Turkish Scientific and Technological Research Council provided partial funding for one researcher. Gauss Center for Supercomputing e.V. computational resources for Julich Supercomputing Center's GCS Supercomputer JUWELS computation time.
Journal Reference:
Meißner U.-G., et al. (2024) Ab Initio Calculation of the Alpha-Particle Monopole Transition Form Factor. Physical Review Letters. doi.org/10.1103/PhysRevLett.132.062501