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An exotic analysis technique adds another piece to the mystery surrounding dark matter



  Illustration of a dark matter puzzle piece

PRISMA + and HIM scientists report the latest results of the CASPEr research program in Science Advances.

A team led by Prof. Dmitry Budker has completed his search for dark matter under the "Cosmic Axion Spin Precession Experiment" (or "CASPEr" for short). The CASPEr Group carries out its experiments in the Cluster of Excellence PRISMA + of the Johannes Gutenberg University Mainz (JGU) and of the Helmholtz Institute Mainz (HIM). CASPEr is an international research program that uses nuclear magnetic resonance techniques to identify and analyze dark matter.

Little is known about the exact nature of dark matter. At present, some of the most promising candidates for dark matter are extremely bright boson particles such as axions, axon-like particles, or even dark photons. "These can also be considered as a classical field that vibrates at a certain frequency. We can not yet quantify this frequency and thus the mass of the particles, "explains Dmitry Budker. "That's why in the CASPEr research program we systematically investigate different frequency ranges for evidence of dark matter."

For this purpose, the CASPEr team develops various special nuclear magnetic resonance (NMR) techniques, each aimed at a specific target frequency range and thus in a certain range of particle masses the dark matter. NMR is generally based on the fact that nuclear spins react to magnetic fields that vibrate at a certain "resonant frequency". The resonance frequency is tuned by a second, normally static magnetic field. The basic idea of ​​the CASPE research program is that a dark matter field can affect the nuclear spins in the same way. As the earth moves through this field, nuclear spins behave as if they are experiencing an oscillating magnetic field, producing a dark matter-induced NMR spectrum.

In the current work, lead author Antoine Garcon and his colleagues used a more exotic technique: ZULF NMR (zero to ultra-low field). "ZULF NMR provides a regime in which nuclear spins interact more strongly with each other than with an external magnetic field," says the author. John W. Blanchard. "In order to make the spins sensitive to dark matter, we only need to apply a very small external magnetic field that is much easier to stabilize." In addition, the researchers first investigated ZULF NMR spectra of 1

3C-formic acid acid for dark matter-induced sidebands using a new analysis scheme for coherently averaging sidebands of arbitrary frequency over several measurements.

This particular form of sideband analysis allowed scientists to search for dark matter in a new frequency range. As the CASPEr team reported in the latest issue of Science Advances no dark matter signal was detected, so the authors were able to exclude ultra-light dark matter with couplings above a certain threshold. At the same time, these results provide another piece of the dark matter puzzle and complement previous CASPEr program results published in June, when scientists studied even lower frequencies using another specialized NMR method called "comagnetometry".

"Like As a puzzle, we combine different parts within the CASPEr program to further narrow the scope of the dark matter search," assures Dmitry Budker. John Blanchard adds, "This is just the first step. We are currently making several promising modifications to increase the sensitivity of our experiment. "

Reference:" Ultra Low Field Nuclear Magnetic Resonance Limitations of Bosonian Dark Matter "by Antoine Garcon, John W. Blanchard and Gary P. Centers, Nataniel L. Figueroa, Peter W. Graham, Derek F. Jackson Kimball, Surjeet Rajendran Alexander O. Sushkov, Yevgeny V. Stadnik, Arne Wickenbrock, Teng Wu and Dmitry Budker, October 25, 2019, Science Advances .
DOI: 10.1126 / sciadv.aax4539


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