Particles on Ice

By Ashley Yeager

Protons, neutrinos and photons take different paths toward Earth. Physicists have to figure out their paths to determine where the particles came from. Credit: Deutsches Elektronen-Synchrotron.

Imagine nabbing the cover of the journal Science. Now, imagine doing it without making a single discovery. For University of Wisconsin physicist Francis Halzen, those dreams came true in 2007.

“We hadn’t done anything by then,” he said during a Nov. 9 physics colloquium as he described the experiment called IceCube.

IceCube is a neutrino detector buried deep in the ice of Antarctica. It did not begin full scientific operations until May 2011. So why did it claim prime Science real estate four years earlier?

Because Halzen and his team were the clear winners in a race, which began in the 1970s, to build a kilometer-wide bucket to capture particles called neutrinos.

To cover just over a half mile of Antarctica with such a detector, Halzen’s team engineered 5,000 neutrino buckets to sit on 86 electronic wires, a bit like strings of Christmas lights. The team then fed each string a mile and a half into the ice near the South Pole.

The idea was that the instrument would detect blue light coming from the reaction of a single neutrino crashing into an ice atom. From that reaction, the physicists could start to tease apart where neutrinos and other high-energy showers of particles, called cosmic rays, come from. Now, the team has also begun adding to the instrument so it can probe what dark matter and dark energy are.

This diagram, superimposed on an aerial photo of the South Pole Station, shows where the 86 detector strands sit. Courtesy of: Tom Gaisser, Univ. of Delaware.

Halzen said studying neutrinos is a lot like taking an X-ray, rather than a normal photo, of the galaxy and the universe. He added that even though there are some promising data points in IceCube’s preliminary scans, no one should get too excited. The neutrino buckets haven’t really seen anything, yet.


It’s a bit like the Large Hadron Collider not seeing the Higgs boson, he said. If scientists don’t see what they are looking for, it will be really interesting and may call for a re-write of the physics textbooks.

But, Halzen said, “I can tell you, we want to see something,” and, doing it before next year, when the discovery of cosmic rays turns a century old, would fulfill another of his physics dreams.

This entry was posted on Thursday, November 10th, 2011 at 4:53 pm and is filed under Field Research, Lecture, Physics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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