Getting No Axion

Washed away

Last year, physicists reported seeing tantalizing experimental traces of the axion, a hypothetical subatomic particle that’s been mentioned as a possible constituent of cosmic dark matter. But the axion was showing up where theory said it shouldn’t be. It now looks as if it wasn’t there after all.

The particle sprang from an attempt to explain certain differences between the strong and weak nuclear forces. Cosmologists seized on the axion because its properties made it a plausible component of dark matter, the unseen material that far outweighs ordinary matter in the universe.
Read the rest of my article, freely available on the Science News Web site.

As I recounted in my end-of-year special last year, MIT physicist Frank Wilczek called the particle after a brand of detergent, because it was supposed to wash away all of the problems of the so-called standard model of particle physics. The brand is not longer sold in the U.S., but it apparently still is in France.

In the latest experiment, researchers attempted to demonstrate the axion’s existence by looking for an effect known as photon regeneration, or, in Zenlike fashion, as “light shining through a wall.” As I write in this week’s Science News:

Researchers shoot a laser beam through a magnetic field toward a metal plate. The metal wall blocks photons, but any axions created in the field would pass through. On the other side of the wall lies a second magnetic field that would convert some of the axions back into photons, making it appear that some photons had passed through.

They detected no axions at all. However, physicists say other types of experiment might have a better chance at discovering the particle. The most intriguing one would look for “light shining through the sun.” As the sun passes in front of a source of gamma rays located far away in the universe, some of the source’s photons could turn into axions. Those would easily zip through the sun, and then perhaps convert back into gamma ray photons, wihch astrophysicists could then pick up.

Wilczek told me that he has kept a box of the U.S.-brand detergent in his basement. Perhaps, if one day the axion is discovered, he could make loads of money by selling it on eBay.

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