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Researchers Harness Antimatter in the Quest for Dark Matter

The BASE Collaboration at CERN joined hands with a research team from the PRISMA+ Cluster of Excellence at Johannes Gutenberg University Mainz (JGU) to perform research that takes an innovative approach toward the search for dark matter.

The scientists are investigating for the first time how dark matter has an impact on antimatter rather than standard matter. The study outcomes were recently reported in the most recent edition of the leading scientific journal Nature.

Those are the findings of a study performed by researchers at Japan’s RIKEN research center, the Max Planck Institute of Nuclear Physics in Heidelberg (MPIK), and the National Metrology Institute Braunschweig (PTB), in collaboration with the Max Planck-RIKEN-PTB Center for Time, Constants and Fundamental Symmetries.

Also part of the study were researchers from CERN, the Johannes Gutenberg University Mainz (JGU), the Helmholtz Institute Mainz (HIM), the University of Tokyo, the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, and the Leibniz University Hannover.

To date, scientists have always conducted high-precision experiments at low energies using matter-based samples in the hope of finding a link to dark matter. Now we’ve decided to search explicitly for interactions between dark matter and antimatter. It is generally assumed that interactions of dark matter will be symmetric for particles and antiparticles. Our study seeks to determine whether this is really the case.

Dr Christian Smorra, Study Lead Author, RIKEN Research Institute

Dr Smorra plans to use an ERC Starting Grant to form a research group at JGU’s Institute of Physics.

In fact, contributors to the project observe a double benefit in this method: Not much is known at this stage about the microscopic properties of dark matter. Currently, a highly debated probable component of dark matter is what is called axion-like particles (ALPs). Furthermore, the standard model of particle physics does not offer any explanation of why there is considerably more matter than antimatter in the universe.

Through our experiments, we hope to find clues that could provide a link between these two aspects,” states Dr Yevgeny Stadnik, who took part in the study as part of a Humboldt Fellowship at HIM. “Possible asymmetrical interactions of this kind have not yet been explored, neither at the theoretical nor at the experimental level. Our current research work is taking a first real step in that direction.”

Captured Antiprotons Could Deliver Insights into Dark Matter

The researchers have focused their attention on a single antiproton that has been trapped in a unique device called a Penning trap. The particle was synthesized by researchers with the help of the Antiproton Decelerator (AD) at CERN, which is the only research institution in the world capable of producing low-energy antiprotons.

Then, the researchers used the BASE Collaboration’s trap system to store and experiment with the antiprotons synthesized at CERN.

An antiproton possesses both charge and spin. Under the influence of a magnetic field, the spin precesses around the magnetic field lines at a highly specific, constant rate—called the Larmor or spin precession frequency.

This means we can detect the presence of dark matter as it influences this frequency. For this purpose, we assume that potential dark matter particles act in the same way as a classical field with a specific wavelength. The waves produced by dark matter pass continuously through our experiment and thus have a periodic effect on the spin precession frequency of the antiproton that would otherwise be expected to remain constant.

Dr Christian Smorra, Study Lead Author, RIKEN Research Institute

The researchers have already investigated a particular frequency range by using their experimental configuration, but were not successful since there was no evidence for the apparent impact of dark matter thus far.

We’ve not yet been able to identify any significant and periodic changes to the antiproton’s spin precession frequency using our current measurement concept,” explains Stefan Ulmer, spokesperson of the BASE Collaboration at CERN.

But we have managed to achieve levels of sensitivity as much as five orders of magnitude greater than those employed for observations related to astrophysics. As a result, we can now redefine the upper limit for the strength of any potential interactions between dark matter and antimatter based on the levels of sensitivity we’ve managed to accomplish.

Stefan Ulmer, Spokesperson, BASE Collaboration at CERN

Merging of Two Research Groups

In effect, the present study combined the efforts of two research teams. The BASE Collaboration at CERN has been successfully performing studies into the fundamental properties of antiprotons for a long time. The team headed by Prof. Dmitry Budker, a researcher at the PRISMA+ Cluster of Excellence at JGU and HIM, is actively involved in the quest for dark matter and offered vital interpretive input to the research.

We determined that there is a great deal of overlap in our research and this resulted in the idea for this new approach in the search for dark matter,” pointed out Dmitry Budker.

In the future, the researchers plan to further improve the precision of measurement of antiproton spin precession frequency—a vital prerequisite for the antimatter-based quest for dark matter to be successful.

In this context, a group led by Prof. Jochen Walz from the Institute of Physics at JGU, working jointly with RIKEN and MPIK, has been devising innovative techniques for cooling protons and antiprotons. At the same time, a team of researchers from PTB Braunschweig, the Leibniz University Hannover, and RIKEN has been executing techniques for quantum logic-based antiproton-spin-state readout.

A wide range of other potential and similar antiparticle-related research works also call for the use of, for instance, antimuons and positrons.


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