WA105 1x1x3 records first particle tracks

Excerpted and adapted from the Symmetry article World’s biggest neutrino experiment moves one step closer, 23 June 2017.

In a lab at CERN sits a very important box. It covers about three parking spaces and is more than a story tall. Sitting inside is a metal device that tracks energetic cosmic particles: the prototype detector WA105 3x1x1, which holds an active volume of five metric tons (3,000 liters) of liquid argon. On June 21, WA105 recorded its first particle tracks.

One of the first tracks in the prototype detector, caused by a cosmic ray.

While ultimately the full-scale DUNE detectors will sit in the most intense neutrino beam in the world, scientists are testing the WA105 3x1x1 components using muons from cosmic rays, high-energy particles arriving from space.

Previous liquid argon neutrino detectors, such as ICARUS and MicroBooNE, detected signals from neutrinos using wires in the liquid argon. But crucially, this new test detector also holds a small amount of gaseous argon, earning it the special status of a two-phase detector. (How it works)

“This is the first time anyone will demonstrate this technology at this scale,” says Sebastien Murphy, who led the construction of the detector at CERN. “The main goal  is to demonstrate that we can amplify charges in liquid argon detectors on the same large scale as we do in standard gaseous TPCs.”

Making sure a dual-phase detector and its electronics work at cryogenic temperatures of minus 184 degrees Celsius (minus 300 degrees Fahrenheit) on a large scale is the primary duty of the prototype detector—but certainly not its only one. The membrane that surrounds the liquid argon and keeps it from spilling out will also undergo a rigorous test. Special cryogenic cameras look for any hot spots where the liquid argon is predisposed to boiling away and might cause voltage breakdowns near electronics.

“The prospect of starting DUNE is very exciting, and we have to deliver the best possible detector,” says André Rubbia, the spokesperson for the WA105 3x1x1 experiment and former co-spokesperson for DUNE. “One step at a time, we’re climbing a large mountain. We’re not at the top of Everest yet, but we’re reaching the first chalet.”

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