Near Daya Bay in China, detectors record the faint flashes produced when antineutrinos hit. Photo­multiplier tubes (shown) pick up the signal. Credit: Roy Kaltschmidt/Lawrence Berkeley National Lab

Heart of the Matter

Neutrinos’ shifty behavior might help explain why the universe has so much stuff in it

By Charles Petit
Web edition: January 10, 2013
Print edition: January 26, 2013; Vol.183 #2 (p. 18)

A golden age for the neutrino is dawning.

A few decades ago, these shy phantoms that flit nearly unfelt through the interstices of the universe seemed mere leftovers in the world of physics.

They outnumber all other particles of matter, whizzing away everywhere — many of them arising in droves from nuclear reactors and nucleosynthesis in stars. Their characteristics made them, to be sure, vitally important building blocks in the 1970s and ’80s for theorists who put together the standard model of physics, describing how fundamental forces and particles fit together. Yet, for decades, neutrinos seemed nearly incapable of doing a lick of work. They were like clowns pouring from a circus car, entertainment for theorists but without important jobs in keeping the cosmos running smoothly.

It is about time for the neutrino to add gravitas. “When I first learned about it in the early 1950s, the neutrino had an odd role in nuclear physics, like that of a sort of crazy uncle who was not all there,” physicist and science writer Jeremy Bernstein wrote in an essay in the March-April 2012 issue of American Scientist.

When asked how the neutrino stacks up today, he says: “It is a wonderful particle. It played an important role in the early universe. I mean, everything about it is mysterious. But back in the 1950s, nobody even gave a goddamn. Maybe I learned about it, but nobody was studying it.”

While neutrinos have been rising in mystery and thus stature for some time, their most recent big break occurred last March. It stemmed from measurements made deep inside a granite mountain not far from Hong Kong. There, an international collaboration — led by an American contingent from the Lawrence Berkeley National Laboratory in California and scientists at the Institute of High Energy Physics in Beijing — has in the last six years built some of the world’s best underground detectors for neutrinos of the specific sort generated inside nuclear reactors.

Read more: Heart of the Matter | Physics | Science News.

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