Tests Of Fundamental Physics With Atomic Parity Violation in Ytterbium

Project Information

YbFUN

Grant agreement ID: 947696

DOI

10.3030/947696

EC signature date 8 October 2020

Start date 1 December 2020

End date 30 November 2026

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 455 244,00

EU contribution

€ 1 455 244,00

Coordinated by

PANEPISTIMIO KRITIS
Greece

Periodic Reporting for period 3 - YbFUN (Tests Of Fundamental Physics With Atomic Parity Violation in Ytterbium)

Reporting period: 2023-04-01 to 2024-09-30

Summary of the context and overall objectives of the project

The project aims to establish a platform for fundamental tests in nuclear and particle physics via precision measurements of parity violation in the atom of ytterbium (Yb). The violation of parity, (i.e. the symmetry with respect to spatial invariance that is of importance in quantum mechanics), arises in an atom primarily due to the effects of the weak force between the atomic nucleus and an orbiting electron.

The project goals are set in order to help address several important questions in fundamental physics. For instance, one important objective is to compare the effects of the weak force in a chain of isotopes of Yb. A precision comparison will allow us to check for the existence of particles beyond those within the Standard Model of particles physics. In addition, this precision isotopic comparison can help address an important question in nuclear physics: what is the size of a neutron-rich (i.e. a heavy) atomic nucleus? This question has proved challenging to tackle since very few methods can probe how the (electrically neutral) neutrons are distributed in the nucleus. Our project will help answer this question by providing information about how the neutron-distribution radius varies among the Yb isotopes. As the neutron-distribution radius in a nucleus is closely connected to the radius of neutron stars (a topic which is currently poorly understood), our work will also provide information to help address this astrophysics problem.

Another objective of the project is to check how the effects of the weak force in an isotope of Yb that has nuclear spin, vary according to the relative orientation of the electron and nuclear spins. Such variations arise due to intranuclear weak forces. How these forces are exerted among nucleons is a field of nuclear physics that is relatively poorly understood. A measurement of the variations would help characterize the underlying intranuclear weak interactions and thus advance the understanding of how these interactions manifest themselves among nucleons.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In the period spanning the first scientific period we focused on implementing necessary upgrades in an apparatus which was previously developed and employed for preliminary parity violation (PV) measurements. The key goal of this set of activities was to obtain enough experimental sensitivity, so that the planned highly precise PV measurements can be undertaken. As a result of the work, we achieved a nearly two-orders-of magnitude improvement, relative to the original apparatus sensitivity. That is, the same accuracy in the measurements of the PV effect in our preliminary experiments, can be now obtained with nearly two-orders-of-magnitude smaller measurement time.

Another major activity we undertook involved detailed studies of systematic effects that are expected to affect our forthcoming PV measurements. These studies are separate for Yb isotopes with zero nuclear spin, and spinful isotopes. For the former case, systematic effects are now well understood, and this opens the way to proceed with our planned isotopic comparison measurements. (At the same time, systematics in the spinful isotopes are still being investigated.)

Early in the project we used part of the setup for a project related to our main ERC project goal: a check for new particles, beyond those included in the Standard Model of particle physics. A previous work had hinted at new particles, and that motivated us to do a complementary check using our Yb apparatus for laser spectroscopy, to validate this possibility. Our results largely diminished the scenario for new particles.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have achieved the largest (by far) experimental sensitivity in any apparatus dedicated to the study of weak interactions in atoms. To within this high degree of experimental sensitivity, we have set systematic effects in our planned measurements under control. This will allow us to proceed with the planned PV experiments with unprecedented sensitivity.

Specifically, we expect by the end of the project to have measured PV effects in a chain of Yb isotopes to approximately 0.05% in each isotope. This will allow for a sensitive check for beyond-Standard model particles as well as to probe the neutron-distribution variation among isotopes. Moreover, such a level of sensitivity will enable us to probe intranuclear weak forces in the isotopes of Yb with nuclear spin.

In addition, by making precision measurements of isotope shifts in an optical transition of Yb, we have evaluated a previously claimed hint for new physics and have shown that the previous observations are highly likely not due to new physics, but instead due to known nuclear-physics effects.