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Giant detector will be used in the next generation of neutrino experiments
By Eran Moore Rea
Across the Atlantic, through the St. Lawrence and four Great Lakes, over the highway from a port in Indiana, finally settling at Fermilab outside of Chicago — ICARUS has finished its journey.
The detector, which holds 600 tons of liquid argon, was transported from outside Gran Sasso in Italy to Fermilab in Batavia, IL. In 2018, ICARUS will begin taking data, ramping up to become one of three detectors for Fermilab’s Short Baseline Neutrino (SBN) program. SBN will be the first of its kind to use two liquid argon detectors to study neutrino oscillations — one at the source and one at a distance.
The hardware and setup of SBN are very similar to Fermilab’s planned Deep Underground Neutrino Experiment (DUNE). Now in the planning stages, the DUNE experiment will shoot neutrinos through Earth from Fermilab to a detector in Lead, South Dakota.
DUNE will also use two liquid argon detectors. For a large enough volume of liquid argon, it becomes statistically likely that even for a beam of famously non-reactive neutrinos, some of them will directly collide with individual argon nuclei. When this collision occurs, physicists can study the particles that are produced from the collision to determine which type of neutrino was involved.
There are already neutrino experiments using liquid argon detectors — MicroBooNE at Fermilab is one — but until now, no experiment has used such detectors in both “near” and “far” locations. These experiments look at the details of neutrino oscillations, in which a neutrino of one type transforms into another type as it travels. Comparing the differences in the neutrino signature between the two detectors allows scientists to study how the particles change.
Specifically, scientists hope they can address an anomaly that’s been debated since it was first seen in the early 2000s. When an earlier experiment called MiniBooNE saw an anomaly in its electron neutrino results that might signal the existence of a fourth type of neutrino, the scientific community responded by setting up new experiments; SBN is one of them. SBN’s detector separation is less than a kilometer, while DUNE’s baseline is nearly 1300 kilometers.
There are already experiments with a near and far detector studying neutrino oscillations; the NOvA experiment based at Fermilab and the T2K experiment in Japan are examples. The advantage of the new experiments, said Sam Zeller, co-spokesperson of MicroBooNE and Fermilab’s Deputy Neutrino Division Head, is that “You can see a lot more of what’s going on in the neutrino interactions” using a liquid argon detector.
“Another technology we might compare this to are Cherenkov detectors, but those detectors operate best at low energy. In order to do the type of physics we want to do, we need to study neutrino oscillation patterns over a much larger range of energies, so you can see the oscillatory structure in the neutrino data,” Zeller said.
ICARUS is the largest particle detector to ever be transported in its complete form. And size matters for neutrinos; as the neutrino beam naturally spreads out over longer and longer distances, researchers need a larger and larger volume of liquid argon to detect them.
During the 2017 APS Division of Particles and Fields meeting, I toured the new home of ICARUS, where personnel from a Spanish shipping company were finishing the installation. Inside the new facility there was what looked like a huge tub waiting for the two truck-sized aluminum-encased ICARUS argon chambers parked outside of the facility.
Currently there are over 200 scientists participating in the SBN program that will include three detectors which are currently at different stages: MicroBooNE is already operating, ICARUS is being installed, and the SBN near detector is in the design stages.
The story of ICARUS is a human story as well as a scientific one, as Peter Wilson, SBN program coordinator, and Cat James, deputy SBN program coordinator, explained to me as we wander around the ICARUS building.
The installation of ICARUS at Fermilab marks the first time that CERN has sent its own personnel — that is, physicists, engineers and technicians that work for CERN, not users employed at other academic institutions — to work on a research collaboration at Fermilab. It’s only in the past few years that CERN has started contributing as a member institution to collaborations centered on instruments not located at CERN. So, while Fermilab has been a member institution of a scientific collaboration at CERN for many years, CERN has only just joined as a member institution of the SBN program at Fermilab.
“Originally there was a proposal to move ICARUS to CERN,” Wilson said, “on a new neutrino beam there. CERN made a strategic decision not to build a new neutrino beam, but to do neutrino physics elsewhere. So what’s happening now is that the neutrino physics community is coming together here at Fermilab.”
The author is a freelance writer based in Minneapolis, Minnesota.
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