Thursday, June 18, 2015
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From symmetry

A goldmine of scientific research

The underground home of the LUX dark matter experiment has a rich scientific history. Photo: Sandbox Studio with Ana Kova

There's more than gold in the Black Hills of South Dakota. For longer than five decades, the Homestake mine has hosted scientists searching for particles impossible to detect on Earth's surface.

It all began with the Davis Cavern.

In the early 1960s, Ray Davis, a nuclear chemist at Brookhaven National Laboratory, designed an experiment to detect particles produced in fusion reactions in the sun. The experiment would earn him a share of the Nobel Prize in physics in 2002.

Davis was searching for neutrinos, fundamental particles that had been discovered only a few years before. Neutrinos are very difficult to detect; they can pass through the entire Earth without bumping into another particle. But they are constantly streaming through us. So, with a big enough detector, Davis knew he could catch at least a few.

Davis' experiment had to be done deep underground; without the shielding of layers of rock and earth it would be flooded by the shower of cosmic rays also constantly raining from space.

Davis put his first small prototype detector in a limestone mine near Akron, Ohio. But it was only about half a mile underground, not deep enough.

"The only reason for mining deep into the earth was for something valuable like gold," says Kenneth Lande, professor of physics at the University of Pennsylvania, who worked on the experiment with Davis. "And so a gold mine became the obvious place to look."

But there was no precedent for hosting a particle physics experiment in such a place. "There was no case where a physics group would appear at a working mine and say, 'Can we move in please?'"

Davis approached the Homestake Mining Company anyway, and the company agreed to excavate a cavern for the experiment.

Read more

Amelia Willamson Smith

Video of the Day

Catching collisions in the LHC

Learn how the detectors at CMS capture and track particles as they are expelled from a collision. View the seven-minute video. Video: Fermilab
Photo of the Day

Feynman fountain

The fountain in front of Feynman Computing Center has been running again. It is a sure sign that summer is here. Photo: Mark Kaletka, CCD
In Brief

Canceled: third-Thursday volunteer cleanup

Today's scheduled third-Thursday volunteer cleanup is canceled due to the wet weather. It will resume next month.

In the News

Neutrino research focuses on Fermilab

From WTTW's Chicago Tonight, June 17, 2015

Editor's note: Neutrino Division Deputy Head Steve Brice talks with WTTW's Eddie Arruza about the Fermilab neutrino program.

Its Tevatron particle collider may have been superseded by the Large Hadron Collider in CERN, Switzerland, but Fermilab remains at the cutting edge of research into the origins of the cosmos. It is now home to research focusing on neutrinos, nearly massless particles that rarely interact with anything. But scientists believe they may have been fundamental to the formation of our universe.

Watch the 10-minute segment

Frontier Science Result: DZero

The directionless universe

The formation of a snowflake or indeed of any crystal spontaneously breaks directional symmetry through the formation of specific special directions. Photo: Wilson Bentley

Disponible en español

A body in uniform motion tends to stay in uniform motion unless acted upon by outside forces, right? Right. And does it matter which direction the motion is in? Nope. There is no special direction in the universe. A Boeing 747 accelerating at 1.5 meters per second per second will be moving fast enough to take off in about a minute, and this will not depend on whether the acceleration is to the east or to the west or in the direction of a Caribbean isle.

At least, not as far as we know. There are certain speculative scenarios arising in string theory in which motion in one direction is slightly different from motion in other directions. The assumption that every direction in space-time is the same is called Lorentz invariance, and it is a fundamental assumption in Einstein's theory of relativity. There is also a different possibility, that of something called spontaneous symmetry breaking in the nature of time and space. This could be an explanation for a previous peculiar DZero result, in which we found that the production of two positive muons differs from that for two negative muons.

Spontaneous symmetry breaking is common. Somewhere, right this minute, snowflakes are forming in some cloud. Every point in the cloud contains water and is pretty much the same as every other point. If the cloud cools to zero degrees Celsius or below, the water molecules will begin to stick together and start to form crystals. The snowflake in the above figure shows three special directions that have spontaneously appeared as a result of its formation. One such direction is left-to-right, and the other two are at 60-degree angles to that direction. Amusingly, the spontaneous breaking of the symmetry of the mist in the cloud is also the creation of a different six-fold symmetry in the shape of the snowflake.

But any difference in motion in one direction through space as compared to other directions has to be pretty small, or we would have noticed it by now. So we would need a very sensitive device to see it.

There is a widely used trick to measure an effect with great sensitivity called interferometry. We can use a certain category of mesons as interferometers. These mesons can decay into either positive or negatively charged muons. Detecting the difference between how often the two electrical charges appear is a sensitive way to look for the possibility of a special direction in the universe. If there is any special direction, the difference in the appearance of negative and positive muons will oscillate with a one-sidereal-day period as the Earth rotates relative to the fixed stars.

DZero has recently examined the asymmetry of the decays of the Bs for a variation with a period of a sidereal day. We do not see any such variation, indicating that there is not any special direction in (at least our part of) the universe. This is the first such search using the Bs meson and is about 10 times more sensitive than earlier indirect searches made about five years ago. Furthermore, the result is sensitive enough to rule out the idea that that unusual dimuon result is a result of Lorentz symmetry breaking.

Leo Bellantoni

Iain Bertram (Lancaster University, England) and Rick Van Kooten (Indiana University) are the primary analysts for this measurement.
The DZero collaboration relies upon many of its collaborators to carefully review analyses for scientific quality before they are released. This analysis was guided to completion by Editorial Board Chair Peter Garbincius (Fermilab) and the physics group conveners, Iain Bertram (not shown), Marj Corcoran (Fermilab), Peter Svoisky (U. Oklahoma) and Daria Zieminska (Indiana University).