Scientists lead a worldwide search for dark matter

A team of researchers have utilised worldwide network optical magnetometers to gather comprehensive data on the search for dark matter.

How did scientists recognise and gather this data?

The international team consisted of six countries worldwide, and included key participation from the PRISMA Cluster of Excellence at Johannes Gutenberg University Mainz (JGU), and the Helmholtz Institute Mainz (HIM). Researchers gathered widespread data on the search for dark matter using a worldwide network of optical magnetometers.

It is widely hypothesised in the scientific community that dark matter fields should produce a characteristic signal pattern in order to be detected by correlated measurements at multiple stations of the Global Network of Optical Magnetometers for Exotic Physics Searches (GNOME).

Analysis of data from a one-month continuous GNOME operation has not yet yielded a corresponding indication. However, researchers have noted that the measurement allows for the constraints on the characteristics of dark matter to be formulated.

What is GNOME and why is it being employed to further dark matter research?

GNOME consists of magnetometers that distributed worldwide including countries such as, Germany, Serbia, Poland, Israel, South Korea, China, Australia, and the United States.

The primary aim for GNOME is to advance the search for dark matter, which is one of the most exciting challenges of fundamental physics in the 21st century. This will offer explanations for many puzzling astronomical observations, such as the rotation speed of stars in galaxies or the spectrum of the cosmic background radiation, which can be best explained by dark matter.

Professor Dmitry Budker, teacher at PRISMA and HIM explained: “Extremely light bosonic particles are considered one of the most promising candidates for dark matter today. These include so-called axion-like particles – ALPs for short. They can also be considered as a classical field oscillating with a certain frequency.

“A peculiarity of such bosonic fields is that – according to a possible theoretical scenario – they can form patterns and structures. As a result, the density of dark matter could be concentrated in many different regions – discrete domain walls smaller than a galaxy but much larger than Earth could form, for example.”

Dr Arne Wickenbrock, co-author of the study, added: “If such a wall encounters the Earth, it is gradually detected by the GNOME network and can cause transient characteristic signal patterns in the magnetometers. Even more, the signals are correlated with each other in certain ways – depending on how fast the wall is moving and when it reaches each location.”

How do magnetometers tie into this research?

The GNOME network consists of 14 magnetometers that are distributed over eight countries worldwide, nine of which provided data for the current analysis. The measurement principle is based on an interaction of dark matter with the nuclear spins of the atoms in the magnetometer.

The atoms are excited with a laser at a specific frequency, orienting the nuclear spins in one direction. A potential dark matter field can disturb this direction, which is then measured by scientists.

“Figuratively speaking, one can imagine that the atoms in the magnetometer initially dance around in confusion. When they ‘hear’ the right frequency of laser light, they all spin together. Dark matter particles can throw the dancing atoms out of balance. We can measure this perturbation very precisely,” explained Doctoral student Hector Masia-Roig, current author of the study.

It is at this stage that the network of magnetometers becomes important. This is because when the Earth moves through a spatially limited wall of dark matter, the dancing atoms in all stations are gradually disturbed, and one of these stations is located in a laboratory at the HIM.

“Only when we match the signals from all the stations can we assess what triggered the disturbance,” said Masia-Roig. “Applied to the image of the dancing atoms, this means: If we compare the measurement results from all the stations, we can decide whether it was just one brave dancer dancing out of line or actually a global dark matter disturbance.”

What future intentions have been generated from this current study?

The research team analysed data from a one-month continuous operation of GNOME in this current study. This resulted in scientists nothing that the statistically significant signals did not appear in the investigated mass range from one femtoelectronvolt (feV) to 100,000 feV.

This means that the researchers can take this into account and narrow down the range in which such signals could theoretically be found even further than before; scientists noted that this is an important result for scenarios that rely on discrete dark matter walls.

Future collaborative work with GNOME will focus on improving both the magnetometers themselves as well as the data analysis; specifically, continuous operation should be even more stable. This is important when it comes to scientists being able to reliably search for signals that last longer than an hour.

Additionally, the previous alkali atoms in the magnetometers are intended to be replaced by noble gases. Under the title Advanced GNOME, researchers expect this to result in considerably better sensitivity for future measurements in the search for ALPs and dark matter.

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