Dragnet for Dark Matter – Worldwide network of optical magnetometers searches for “dark” field patterns – scinexx.de

The search continues: A worldwide network of optical magnetometers has started the search for dark matter and its still undiscovered particles. If this exotic form of matter consists of axions or other light bosons, then they could influence the spins of atoms in a concentrated form – and therefore make themselves felt in the optical magnetometers. In the first month of measurements, however, the GNOME network did not find anything.

Dark matter makes up more than 80 percent of all matter in the cosmos, but what it is made of is still a mystery. Attempts to detect dark matter particles using a wide variety of detectors have so far been largely in vain. As a result, some candidates such as Weakly Interacting Massive Particles (WIMPs) or sterile neutrinos are now considered unlikely, while axions or other “dark” bosons are the focus of the search.

Distribution of magnetometers in the GNOME network. © Hector Masia Roig

“Dark” fields disrupt atomic spins

A new way to detect axions and similar potential dark matter particles is the GNOME network (Global Network of Optical Magnetometers for Exotic Physics Searches). This is based on a potential property of the axion-like particles that is also typical of other bosons: “They can also be viewed as a classical field that oscillates at a certain frequency,” explains co-author Arne Wickenbrock from the University of Mainz.

The decisive factor, however: “A peculiarity of such bosonic fields is that they can – according to a possible theoretical scenario – form patterns and structures,” Wickenbrock continues. “For example, discrete domain walls could form that are smaller than a galaxy but much larger than Earth.” If the Earth flies through such a “wall” of dark matter, the axion-like particles with the directed spins would have to of atoms interacting in a magnetic field.

Worldwide measuring network

The GNOME network uses exactly this effect. In the magnetometers distributed in 14 countries worldwide, a laser excites the spins of the measuring atoms so that they all point in the same direction. Now, if a potential dark matter field comes within range of these magnetometers, it should deflect the atomic spins. “Dark matter particles can unbalance the dancing atoms. We can measure this disturbance very precisely,” says Wickenbrock’s colleague Hector Masia-Roig.

The signal from a bosonic field of axions should therefore be detectable as a perturbation that sequentially captures the globally distributed magnetometers at a certain rate. “Only when we compare the signals from all stations can we assess what caused the disruption,” says Masia-Roig.

No hits so far

However: Preliminary measurements with nine of the 14 magnetometer stations have so far not been able to detect any effects from axion-like particles. In the four search runs between 2017 and 2020, the GNOME team primarily scanned the energy ranges up to 400.0e0 gigaelectronvolts and found no statistically significant signals. This further narrows the range in which such particles could exist, the researchers said.

For the further manhunt, the magnetometers of the GNOME network and the data analysis are to be improved so that longer continuous measurements are possible. This is important to reliably look for signals lasting longer than an hour. In addition, the existing alkali atoms in the magnetometers are to be replaced by noble gases, as the team explains. Overall, this will give the measurement network greater sensitivity. (Nature Physics, 2021; doi: 10.1038/s41567-021-01393-y)

Source: Johannes Gutenberg University Mainz


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