UCI Professor Henry Sobel- Ghostly Particle Could Solve Cosmic Mystery

The two famously annihilate when they come into contact, suggesting a kind of conflagration in the early universe. But why, exactly, did matter win?

The transformation of a ghostly particle called the neutrino could help solve a mystery that has haunted physics for decades: Why so much matter in the universe, and so little antimatter?

The two famously annihilate when they come into contact, suggesting a kind of conflagration in the early universe. But why, exactly, did matter win?

Scientists, including UC Irvine’s Hank Sobel, announced this week that a massive detector in Japan had picked up signs of neutrinos of one “flavor” changing into another as they traveled underground.

Such events are very difficult to detect; neutrinos, streaming through us by the billions, rarely interact with matter at all as they sail through the cosmos.

But the detection could be the first step toward solving the antimatter riddle.

If scientists can measure one type of neutrino transforming into another, they also should be able to see antineutrinos turning into another antineutrino flavor, Sobel said.

The key question: Is the probability of such a transformation different for neutrinos and antineutrinos?

That would be a “violation” of sorts — a “charge-parity” violation in physics speak. It would reveal a fundamental difference in the way matter and antimatter interact.

And that difference could explain how matter came to dominate the universe, trouncing its opposite number.

“Since the Universe today is rich in matter, but has very little anti-matter, one possibility is that some difference in how matter and anti-matter behaved in the early Universe generated this result,” Sobel, working in Japan this week, said via email.

Sobel is a UC Irvine physics and astronomy professor who is co-spokesperson for Japan’s Super-Kamiokande detector and whose research group handles part of the detector’s operation and analysis.

To make their observations, scientists fired a beam of neutrinos over a distance of some 185 miles, from the Proton Accelerator Research Complex on the Japanese east coast to the giant Super-Kamiokande detector near the country’s west coast.

Super-Kamiokande is a huge stainless steel tank filled with 50,000 tons of ultrapure water built in a mine more than 3,200 feet underground.

So the neutrino beam makes its journey through the Earth itself, hitting nothing on the way down.

The big tank is also filled with 13,000 “photo multipliers,” which can pick up a telltale flashes of light from the occasional strike neutrinos make as they pass through the water.

The impression of the light on the photomultipliers reveals the kind of particle that passed through.

Out of 88 neutrino events picked up by the detector between January 2010 and Mar. 11—when the massive Japanese earthquake and tsunami interrupted the experiment — six were identified as “electron” neutrinos.

Since they started their trip from the Proton Accelerator as “muon” neutrinos, scientists concluded that they had transformed themselves along the way.  More experiments are planned by the end of this year.