Building big experiments to study very little things

When I think of an experiment, I think of some flasks, a pipette, maybe an incubator. But to a particle physicist, an experiment can be a machine bigger than a house, designed to study subatomic particles.

There’s a certain charm to the fact that such vast equipment has to be constructed to study the smallest known bits of matter. The tunnel of the Large Hadron Collider has a circumference of almost 27 kilometers. And KATRIN, an experiment in Karlsruhe, Germany, described by physics writer Emily Conover in this issue, requires a blimplike metal tank that’s wider than some of the neighborhood streets.

Conover knows firsthand the exacting work of building a physics experiment. While a graduate student at the University of Chicago, Conover toiled away on Double Chooz. The experiment was designed to detect antineutrino oscillations, which occur when antineutrinos change from one type into another.

That endeavor required a source of antineutrinos. They’re produced during certain nuclear reactions, so the experiment was located in a tunnel near a nuclear power plant in Chooz, France. It also required detectors to spot heavy relatives of electrons called muons, which constantly rain down on Earth and can cause reactions that mimic antineutrinos. The detectors, which included scintillators that would light up when a muon zipped through, made sure muons didn’t get counted as antineutrinos by mistake. 

Conover and her colleagues used an extruder to form hundreds of thin, 3-meter-long strips of plastic, then assembled them to make the detectors.  “They were kind of floppy and covered with aluminum,” Conover says of the detectors. “We were always terrified that we would break one.”

The project involved taking several trips to France to install and test the detectors in the subterranean tunnel. All told, Conover worked on Double Chooz for six years. In the end, the experiment was a success: It was one of the first to measure a particular type of neutrino oscillation.

Scientists come in many flavors, and we’re delighted to provide a behind-the-scenes look at their work across the disciplines.