The dark matter experiment reveals no trace of axions

Axions are particularly unusual in that they are supposed to change the rules of electricity and magnetism to a tiny level. In an article published today in Letters of physical examination, the MIT-led team reports that during the first month of observation, the experiment did not detect any signs of axion between 0.31 and 8.3 nanoelectronvolts. This means that the axions included in this mass range, which equates to about one-fifteenth of the mass of a proton, do not exist or that they have an even lower effect on the 39, electricity and magnetism than previously thought.

"This is the first time we have looked directly at this axion space," says Lindley Winslow, Senior Researcher Experienced and Assistant Professor of Physics for Professional Development, Jerrold R. Zacharias at MIT. "We are excited to be able to say now:" We have a way to look here and we know how to do better! "

WIT co-authors include lead authors Jonathan Ouellet, Chiara Salemi, Zachary Bogorad, Janet Conrad, Joseph Formaggio, Joseph Minervini, Alexey Radovinsky, Jesse Thaler and Daniel Winklehner, as well as researchers from eight other institutions.

Magnetars and Munchkins

Although they are supposed to be everywhere, axions should be virtually like ghosts, having only tiny interactions with everything in the universe.

"As dark matter, they should not affect your everyday life," says Winslow. "But we think that they affect things on a cosmological level, like the expansion of the universe and the formation of galaxies that we see in the night sky."

Due to their interaction with electromagnetism, it is assumed that axions have surprising behavior around magnetars, a type of neutron star producing an extremely powerful magnetic field. If axions are present, they can exploit the magnetic field of the magnetar to become radio waves that can be detected with specialized telescopes on Earth.

In 2016, a trio of theorists from MIT developed a thought experiment for axion detection, inspired by magnetar. The experiment, called ABRACADABRA, was designed by Thaler, an associate professor of physics and a researcher at the Nuclear Science Laboratory, for the purpose of the broadband / resonant resonance approach to the detection of the cosmic axion. Center for Theoretical Physics, with Benjamin Safdi, then member of MIT Pappalardo, and former graduate student Yonatan Kahn.

The team proposed to design a small donut-shaped magnet kept in the refrigerator at a temperature just above absolute zero. Without axions, there should be no magnetic field in the center of the donut or, as Winslow says, "where the munchkin should be". However, if axions exist, a detector must "see" a magnetic field in the middle of the donut

Once the group published its theoretical project, Winslow, an experimentalist, set out to find ways to actually build the experiment.

"We wanted to look for the signal of an axion where, if we see it, it's really axion," says Winslow. "This is what was elegant in this experiment.Technically, if you see this magnetic field, it can only act axion, because of the particular geometry to which they thought . "

In the sweet spot

This is a difficult experience because the expected signal is less than 20 atto-Tesla. For reference, the Earth's magnetic field is 30 micro-Tesla and the human brain waves are 1 pico-Tesla. During the construction of the experiment, Winslow and his colleagues had to face two major design challenges, the first of which was to use the refrigerator to maintain all the experience at ultra-cold temperatures . The refrigerator included a mechanical pump system whose activity could generate very slight vibrations which, according to Winslow, could mask an axion signal.

The second challenge involved noise in the environment, such as that generated by nearby radio stations, the activation and deactivation of electronics throughout the building and even the LED lights of computers and electronics, likely to generate competing magnetic fields.

The team solved the first problem by suspending the entire device, using a wire as thin as the floss. The second problem was solved by a combination of superconducting cold shielding and hot shielding around the experiment.

"We could finally take data, and there was a soft region in which we were above the vibrations of the refrigerator and below the environmental noise probably coming from our neighbors, in which we could experience. "

The researchers first performed a series of tests to confirm that the experiment was working and presenting the magnetic fields accurately. The most important test was to inject a magnetic field to simulate a false axion and see if the detector of the experiment was producing the expected signal, which would indicate that if a real axion interacted with the experiment, it would be detected. At this point, the experiment was ready to go.

"If you take the data and use it in an audio program, you can hear the sounds from the refrigerator," says Winslow. "We also see other noises coming and going from the neighbor who does something, then that noise disappears, and when we look at that privileged place, everything is held together, we understand how the detector works and becomes silent enough to hear the axions. "

Seeing the swarm

In 2018, the team conducted the first trial of ABRACADABRA, sampling continuously between July and August. After analyzing the data for this period, they found no axions in the mass range between 0.31 and 8.3 nanoelectronvolts that change the electricity and magnetism of more than one part in 10 billion.

The experiment is designed to detect axions of even smaller masses, up to about 1 femtoelectronvolts, as well as axions up to 1 microelectronvolts.

The team will continue the current experiment, which is about the size of a basketball, to look for even smaller and weaker axions. At the same time, Winslow is finding a way to expand the size of a compact car, with dimensions that could detect even weaker axions.

"There is a real possibility of a great discovery in the next steps of the experiment," explains Winslow. "What motivates us is the ability to see something that would change the field.This is a high-risk and highly profitable physics."

Explore further:
The team simulates a magnetar to search for a dark matter particle

More information:
Design and implementation of dark matter research ABRACADABRA-10 cm axion, journals.aps.org/prd/accepted/… a284b0eb5cd5d60ea137