CERN Experiment Hunts For Axions And Chameleons — Hypothetical Dark Matter And Dark Energy Particles

On Sunday, when the sun made its annual alignment with the black hole at the center of our galaxy, scientists at the European Organization for Nuclear Research (CERN) trained their sights on the celestial event. Their aim in doing so? To detect and study hypothetical entities called axions and chameleons — particles that may constitute dark matter and dark energy, respectively.

The scientists used the CERN Axion Solar Telescope (CAST) — a device originally designed to detect axions and chameleons that our sun may be emitting — to focus on the black hole at the center of the Milky Way. The hope was that the sun’s gravitational force would act as a lens that would warp the fabric of space-time behind it, thereby focusing slow-speed exotic particles that the supermassive black hole may be emitting.

“We’ve always looked for exotic particles from the Sun, we have been doing this for years, but for one specific day we can look beyond the sun, to see if something more happens,” CAST experiment spokesman Konstantin Zioutas said in a statement released Monday. “The galactic centre might send out exotics that we can detect now, which might tell us far more about the dark universe than we could know before, since the Sun can amplify a faint exotic stream by about one billion, provided it is aligned with the Sun-Earth system.”

The existence of axions is predicted by an extension of quantum chromodynamics, which is a theory that lies within the ambit of the Standard Model of particle physics and explains how the strong nuclear force — one of the four known fundamental forces — works. Some estimates suggest that if axions do make up the bulk of dark matter, they would have a mass of between 50 and 1,500 microelectronvolts, making them up to 10 billion times lighter than electrons.

Chameleons, meanwhile, have been theorized to exist to explain what dark energy — the mysterious force that makes up over 68 percent of the universe — is made of. As its name suggests, it is a hypothetical particle capable of changing its properties based on its surroundings — gaining and losing mass as required.

“If matter were music, then ordinary matter would be like the keys on a piano,” Amol Upadhye, a theoretical physicist at the University of Wisconsin, explained in an interview with Symmetry magazine. “Each particle has a discrete mass, just like each piano key plays a single note. But chameleon particles would be like the slide on a trombone and able to change their pitches based on the amount of background noise.”

However, even if these particles do exist, it has hitherto been impossible to detect their interactions with normal matter as they are invisible to most detectors.

“Until now, it’s been impossible to detect particles through their specific direct interaction with matter because the equipment didn’t exist. We had to build a special detector, called KWISP (Kinetic Weakly Interacting Slim Particle detector),” Giovanni Cantatore, deputy spokesman for CAST, said in the statement. “KWISP uses a special membrane force sensor — like the skin of a drum. When it’s hit by the chameleons, it vibrates at a frequency we can fix using the ‘chameleon chopper’, a device we invented for this purpose.”

Researchers at CERN are now analyzing data gathered during Sunday’s experiment, although preliminary results indicate that no new particles were detected emanating from the black hole.