Physicists have narrowed the search space for dark matter. But the axion has not yet been caught

(ORDO NEWS) — CERN scientists are looking for a particle of dark matter – the axion. So far no success. And all experiments end in failure.

But at the CAST facility, which is supposed to register photons interacting with axions, some progress has been made.

If hypothetical particles called axions were found, they could solve two mysteries at once: explain what dark matter is made of (made of axions) and explain the symmetry properties of the strong force that keeps protons and neutrons in atomic nuclei.

Scientists are trying to look not for the axions themselves (this is impossible at the current level), but for traces of their interaction with other particles, in particular with photons.

In their article , a team of researchers working on the CAST experiment at CERN, Geneva, reports how they refocused part of the experiment on a previously unexplored axion search area.

CAST was originally designed to search for axions coming from the Sun. But in the new study, the CAST team has set up an axion detector that is now looking for axions from the Milky Way’s dark matter halo. The detector was named CAST-CAPP.

Hunting for dark matter

Physicists have narrowed the search space for dark matter But the axion has not yet been caught 2
The CAST-CAPP resonator was placed inside the CAST magnet (blue)

In the strong magnetic field generated by the CAST magnet, axions should turn into photons (at least in theory).

The detector is actually a radio receiver that researchers can tune to determine the frequency of these axion-generated photons.

But the frequency of the “radio station” transmitting axions is unknown, so the researchers slowly scanned the entire frequency band where an axion signal is theoretically possible.

CAST-CAPP can be configured to receive axion signals in the range of 4.774 to 5.434 GHz, which corresponds to axion masses from 19.74 to 22.47 microelectronvolts (this is very small – about a million million times less than the mass of an electron).

The researchers scanned the entire band at 200 kHz steps for 4124 hours from September 12, 2019 to June 21, 2021, and did pick up some background signals.

For example, they noticed local WiFi at 5 GHz, but no signals were received from the axions. But physicists believe that not everything is hopeless.

The CAST-CAPP data impose new restrictions on the maximum force of interaction between axions and photons for axion masses from 19.74 to 22.47 microelectronvolts, narrowing the space in which one can search for axion dark matter.

The hunt for dark matter continues. The Large Hadron Collider may also join it in the distant future.

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