The team led by prof. Dmitry Budker continued his search for dark matter as part of the "Space Axis Spin Precession Experiment" (abbreviated as "CASPEr"). The CASPEr Group conducts experiments in the PRISMA + Cluster of Excellence at the Johannes Gutenberg University in Mainz (JGU) and the Helmholtz Institute Mainz (HIM). CASPEr is an international research program that uses nuclear magnetic resonance techniques to identify and analyze dark matter.
Very little is known about the exact nature of dark matter. Currently, one of the most promising candidates for dark matter are extremely light boson particles, such as axons, axion-like particles, and even dark photons. "They can also be considered a classic field oscillating at a certain frequency. But we can't yet determine this frequency – and therefore the mass of the particles, "explains Dmitry Budker. "Therefore, in the CASPEr research program, we systematically examine different frequency ranges, looking for traces of dark matter."
To this end, the CASPEr team is developing various special nuclear magnetic resonance (NMR) techniques, each of which is targeted at a specific frequency range, and therefore a specific mass range of dark matter particles. NMR generally means that nuclear spins react to magnetic fields oscillating at a certain "resonant frequency."
The resonance frequency is tuned by a second, usually static magnetic field. The basic idea of the CASPEr research program is that the field of dark matter can affect nuclear spins in the same way. When the Earth moves through this field, nuclear spins behave as if they have experienced a vibrating magnetic field, thus generating a dark matter-induced NMR spectrum.
In the current work, the first author Antoine Garcon and his colleagues used a more exotic technique: ZULF (from zero to ultrasonic field) NMR. "ZULF NMR provides a regime in which nuclear spins interact more strongly with each other than with an external magnetic field," says correspondent author Dr. John W. Blanchard. "To sensitize spins to dark matter, all we have to do is apply a very small external magnetic field that is much easier to stabilize."
In addition, for the first time, researchers examined 13C-formic acid ZULF NMR spectra for dark matter-induced sidebands, using a new analysis scheme to consistently averaged sidebands at any frequency in multiple measurements.
This particular form of sideband analysis has enabled scientists to search for dark matter in a new frequency range. No dark matter signal was detected, according to the CASPEr team in the latest issue of Science Advances, allowing authors to exclude ultra-light dark matter with couplings above a certain threshold.
At the same time, these results are another element of the dark matter puzzle and complement the previous results of the CASPEr program reported in June, when scientists studied even lower frequencies using another specialized NMR method called 'comagnetometry'.
"Like puzzles, we combine different elements in the CASPEr program to further narrow the search for dark matter," says Dmitry Budker. John Blanchard adds: "This is just the first step. We are currently implementing some very promising modifications to increase the sensitivity of our experiment. "
Johannes Gutenberg Universitaet Mainz
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Physicists have found a way to "hear" dark matter
Stockholm, Sweden (SPX) October 10, 2019
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