LArIAT Upgrade Tests DUNE Design

Scientists from the LArIAT experiment at Fermi National Accelerator Laboratory (CSA CSM) have begun a proof-of-concept test for the planned Deep Underground Neutrino Experiment (DUNE). The researchers are studying what will happen if the space between detection wires inside the future DUNE detectors is increased from three millimeters to five, a design that could help reduce cost.

Like the future DUNE detectors, LArIAT is filled with liquid argon. When a particle strikes an argon nucleus inside the detector, the interaction creates electrons that float through the argon until they’re captured by a wire that registers a signal. Scientists then measure the signal to learn about the particle interaction.

Unlike the DUNE detectors, LArIAT does not detect neutrinos. Rather, it uses the interactions of other particle types to make inferences about neutrino interactions. And very unlike DUNE, LArIAT is the size of a mini-fridge, a mere speck compared to DUNE’s detectors, which will hold about 22 Olympic-size swimming pools’ worth of liquid argon.

For the test, LArIAT scientists use a beam of charged particles provided by the Fermilab Test Beam Facility that is fired into the liquid argon. These particles interact with matter far more than neutrinos do, so the beam results in many more interactions than a similar beam of neutrinos that would mostly pass through the argon. The higher level of interactions is what allows LArIAT to forgo the massive size of DUNE.

Results from LArIATmay help physicists better understand other liquid-argon neutrino detectors at the lab that use three-millimeter spacing, such as MicroBooNE and SBND. “The point of the LArIAT experiment is to measure how well we can identify the various types of particles that come out of neutrino interactions and how well we can reconstruct their energy,” says Jen Raaf, LArIAT spokeswoman.

Although LArIAT doesn’t detect neutrinos, the charged-particle interactions can give scientists clues about how neutrinos interact with argon nuclei. “Instead of sending a neutrino in and looking at what stuff comes out, you send the other stuff in and see what it does,” Raaf says.

Interactions in LArIAT are characterized primarily by a mesh of wires that detects the drift electrons. One key factor that affects the accuracy of drift-electron detection is the spacing between each wire. The closer together the wires, the better the spatial resolution, according to Raaf. But the more closely spaced the wires are, she says, the more wires that are needed. More wires mean more electronics to detect signals from the wires, which can become expensive in a giant detector such as DUNE.

LArIAT uses the Fermilab Test Beam Facility. Its test beam originates from the lab’s accelerators and passes through a set of particle detection instruments before arriving at the LArIAT detector. Scientists can then compare the results from the first set of instruments with the LArIAT results.

“If you know that it was truly a pion going into the detector, and then you run your algorithm on it and it says ‘Oh, no, that was an electron,’ you’re like ‘I know you’re wrong!’” Raaf says. “So you just compare how often you’re wrong with five millimeters versus three millimeters.” Simulations suggest that the increase to five-millimeter spacing should work, but it’s up to Raaf and her team to test whether or not 5-millimeter spacing will do the job. “It works in theory, but we always like to measure,” she says.