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.

This is a prototype detector, a stepping-stone on the way to the future Deep Underground Neutrino Experiment (DUNE). On June 21, it recorded its first particle tracks.

So begins the largest ever test of an extremely precise method for measuring elusive particles called neutrinos, which may hold the key to why our universe looks the way it does and how it came into being.

A two-phase detector

The prototype detector is named WA105 3x1x1 (its dimensions in meters) and holds five active tons—3000 liters—of liquid argon. Argon is well suited to interacting with neutrinos then transmitting the subsequent light and electrons for collection. 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.

As particles pass through the detector, they interact with the argon atoms inside. Electrons are stripped off of atoms and drift through the liquid toward an “extraction grid,” which kicks them into the gas. There, large electron multipliers create a cascade of electrons, leading to a stronger signal that scientists can use to reconstruct the particle track in 3D. Previous tests of this method were conducted in small detectors using about 250 active liters of liquid argon.

“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 3x1x1 test detector represents a big jump in size compared to previous experiments, but it’s small compared to the end goal of DUNE, which will hold 40,000 active tons of liquid argon. Scientists say they will take what they learn and apply it (and some of the actual electronic components) to next-generation single- and dual-phase prototypes, called ProtoDUNE.

The technology used for both types of detectors is a time projection chamber, or TPC. DUNE will stack many large modules snugly together like LEGO blocks to create enormous DUNE detectors, which will catch neutrinos a mile underground at Sanford Underground Research Facility in South Dakota. Overall development for liquid argon TPCs has been going on for close to 40 years, and research and development for the dual-phase for more than a decade. The idea for this particular dual-phase test detector came in 2013.

“The main goal [with WA105 3x1x1] is to demonstrate that we can amplify charges in liquid argon detectors on the same large scale as we do in standard gaseous TPCs,” Murphy says.

By studying neutrinos and antineutrinos that travel 800 miles through the Earth from the US Department of Energy’s Fermi National Accelerator Laboratory to the DUNE detectors, scientists aim to discover differences in the behavior of matter and antimatter. This could point the way toward explaining the abundance of matter over antimatter in the universe. The supersensitive detectors will also be able to capture neutrinos from exploding stars (supernovae), unveiling the formation of neutron stars and black holes. In addition, they allow scientists to hunt for a rare phenomenon called proton decay.

“All the R&D we did for so many years and now want to do with ProtoDUNE is the homework we have to do,” says André Rubbia, the spokesperson for the WA105 3x1x1 experiment and former co-spokesperson for DUNE. “Ultimately, we are all extremely excited by the discovery potential of DUNE itself.”

Testing, testing, 3-1-1, check, check

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.

After many months of hard work, the cryogenic team and those working on the CERN neutrino platform have already successfully corrected issues with the cryostat, resulting in a stable level of incredibly pure liquid argon. The liquid argon has to be pristine and its level just below the large electron multipliers so that the electrons from the liquid will make it into the gaseous argon.

“Adding components to a detector is never trivial, because you’re adding impurities such as water molecules and even dust,” says Laura Manenti, a research associate at the University College London in the UK. “That is why the liquid argon in the 311—and soon to come ProtoDUNEs—has to be recirculated and purified constantly.”

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. These efforts are supported by many groups, including the Department of Energy’s Office of Science.

The plan is now to run the experiment, gather as much data as possible, and then move on to even bigger territory.

“The prospect of starting DUNE is very exciting, and we have to deliver the best possible detector,” Rubbia says. “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.”

Singer-songwriter Howie Day was sitting in a coffee shop in Denver one morning while on tour when he saw the Twitter notifications: CERN had shared a parody video of his hit song “Collide,” sung from the perspective of a proton in the Large Hadron Collider.

Sarah Charley, US communications manager for the LHC experiments, had come up with the idea for the video. She created it with the help of graduate students Jesse Heilman of the University of California, Riverside and Tom Perry and Laser Seymour Kaplan of the University of Wisconsin, Madison.

They spent lunches and coffee breaks workshopping their new version of the lyrics, which were originally about two people falling in love despite their differences. They spent a combined 20 hours in CERN’s editing studio recording the vocals and instrumentation of the track. Then they wandered around the laboratory for a full Saturday, filming at various sites. Charley edited the footage together.

“I was flattered, and it was quite funny, too,” Day says of seeing the video for the first time. “I immediately retweeted it and then sent a direct message inquiring about a visit. I figured it was a long shot, but why not?”

That started a conversation that led to Day planning a visit to CERN and booking time in his studio to re-record the song from the ground up with the new lyrics. “It was about the most fun I've ever had in the studio,” Day says. “We literally laughed all day long. I sent the track off to CERN with the note, ‘Should we make another music video?’”

The answer was yes.

While at CERN, Day spent two days visiting the ATLAS and CMS experiments, the CERN Data Centre and the SM18 magnet-testing facility. He also was given the rare opportunity to travel down into the LHC tunnel. CERN’s video crew tagged along to film him at the various sites.

“Going down into the LHC tunnel was a once in a lifetime opportunity, and it felt that way. It was like seeing the northern lights, or playing the Tonight Show, or bringing a new puppy home.”

Day, who says he has always been fascinated by the “why” of things, had been aware of CERN before this project, but he had only a rough idea of what went on there. He says that it wasn’t until he got there that things started to make sense.

“Obviously nothing can prepare you for the sheer scale of the place, but also the people who worked there were amazing,” Day says. “I felt completely overwhelmed and humbled the entire time. It was truly great to be working at the site where humans may make the most important scientific discoveries of our lifetime.”

Heilman, now a postdoctoral researcher at Carleton University, says that he saw the song as a way to reach out to people outside the culture of academia.

“All of us have been steeped in the science for so long that we sort of forget how to speak a language,” he says. “It's always important for academics and researchers to learn different ways to communicate what we’re doing because we’re doing it for people and for society.”

There’s a point in the original song where there’s an emotional build, he says, and Day sings, “I’ve found I’m scared to know, I’m always on your mind.”

The parody uses that part of the song to express the hopes and fears of experimentalists looking for evidence that might not ever appear.

“We're all experimentalists, so we will all spend our careers searching for something,” Heilman says. “The feeling is that [the theory of] supersymmetry, while it's this thing that everybody's been so excited about for a long time, really doesn’t seem that likely to a lot of us anymore because we’re eliminating a lot of the phase space. It's sort of like this white whale hunt. And so our lyrics, ‘Can SUSY still be found?’ is this emotional cry to the physics.”

Charley says she hopes that, through the video, they’re able to “reach and touch people with the science who we normally can't talk to.”

“I think you can appreciate something without fully understanding it,” she says. “As someone who is a professional science communicator, that's always the line I'm walking: trying to find ways that people can appreciate and understand and value something without needing to get a PhD. You can't devote your life to everything, but you can still have an appreciation for things in the world outside your own specific field.”