Physics

Antimatter Cosmic Rays Shine a Gentle on Mysteries of the Universe

Nobel Laureate Samuel Ting laughed after I requested the place the entire excessive vitality electrons that hit his particle detector have been coming from. “The info has simply been printed three days in the past,” he informed me, hinting on the depth of the thriller and the advantage of persistence. “A very powerful factor is that none of our outcomes might be defined by present fashions.”

NASA Picture: ISS028E016133 – Exterior view of the Worldwide House Station (ISS) taken throughout a session of Extravehicular Exercise (EVA) with a fisheye digital camera. The shuttle Atlantis is partially seen docked to the Node 2/Unity and the Alpha Magnetic Spectrometer – 02 (AMS-02) is seen within the foreground.
That unexplained knowledge is the vitality distribution of 28 million electrons that have been intercepted by AMS, the Alpha Magnetic Spectrometer, as they tore by the universe at practically the pace of sunshine. It’s the topic of analysis just lately printed within the American Bodily Society’s journal Bodily Assessment Letters by the AMS collaboration.

Ting has led the AMS experiment because it was nothing greater than a wild thought 25 years in the past, however he hasn’t seen the detector since 2011. No less than not in particular person. That’s as a result of it’s mounted to the surface of the Worldwide House Station (ISS).

Why house? Though it might appear largely empty, particles known as cosmic rays are always zooming by house in all instructions. Some are ejected by the solar and different stars. Many—the upper vitality ones—are produced by supernovas and different cosmic engines. Some are the product of particle decays or collisions between particles. All of them comprise details about the universe that’s tough to entry in different methods.

Detecting particles in house is like viewing a room with the lights on for the primary time, explains Ting. A room that might reveal the character of darkish matter, antimatter, and cosmic rays.

AMS isn’t the primary space-based particle detector, however it’s the largest and longest enduring. It’s additionally the one space-based detector that may distinguish between the electrons and their antiparticles, positrons, in cosmic rays. That is key: at a basic degree, we nonetheless don’t know why there’s extra matter within the universe than antimatter. However among the finest locations to seek out clues are within the distribution and origin of particles and their antiparticles.

AMS measures the cost, velocity, path, and vitality of cosmic rays. Cosmic rays are infamous for colliding with atoms within the Earth’s higher environment, so AMS was designed to intercept them earlier than that occurs. It might distinguish between electrons and positrons by how they react to a magnetic area, on this case produced by a cylindrically formed magnet with a area three,000 instances extra intense than that of the Earth. The detector weighs 7.5 tons. (Placing a powerful magnet on the ISS is harmful enterprise and took 17 years of cautious planning. That’s an enchanting story for one more day.)

For the final eight years, knowledge has been streaming from the ISS to AMS management room at CERN in Switzerland. Ting ponders the information from there or his workplace on the Massachusetts Institute of Expertise. A whole lot of collaborators from 16 completely different nations do the identical of their respective places of work.

In January, the collaboration printed the vitality distribution of cosmic ray positrons detected over a 6.5-year interval. They discovered that almost all low-energy positrons have been produced by cosmic ray collisions and that top ones have been produced by an unknown supply up till a cutoff vitality, above which no positrons have been detected. This newest result’s primarily based on the cosmic ray electrons detected over the identical time span. “What we discovered is that electrons have completely completely different spectra than positrons,” says Ting. Particularly, the AMS collaboration discovered a lot smaller fraction of the lower-energy electrons have been produced by cosmic ray collisions than positrons. And there was one other huge distinction—no proof of an vitality cutoff for electrons. Collectively, these outcomes recommend that the positrons and electrons have completely different origins.

Earlier than AMS, cosmic ray experiments evaluating positrons to electrons had large errors—round 30% or extra. “When you might have massive errors, you may accommodate many theories,” Ting informed me. With the precision of AMS, that area of workable theories is vanishingly small. That presents an infinite alternative to be taught and discover.

The place do the surplus positrons come from? Darkish matter collisions? A close-by pulsar? Above the cutoff, are there are actually no positrons, or simply only a few? What concerning the excessive vitality electrons? Are they produced in supernovas and/or another cosmic occasion? Why are the 2 spectra so completely different?

As AMS continues to gather this distinctive knowledge, new fashions shall be proposed. New questions will come up. And perhaps, if we’re affected person, new solutions shall be discovered.

—Kendra Redmond


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