Neutrinos’ claim to fame is it’s the most abundant massive particle in the universe according to Fermilab. But, just because there are a lot of them doesn’t mean we fully understand them. Researchers know neutrinos come in three types, but differentiating them has proven difficult.
Which one is the heaviest? Which one is the lightest? Those are the questions Fermilab is trying to answer with the NuMI Off-Axis Electron Neutrino Appearance (NOvA) experiment.
On August 7th, scientists attached to the experiment announced they are one step closer to answering these questions. They reported the first evidence of oscillating neutrinos. Why is this important? It confirms the detector built for the project is functioning as expected.
“People are ecstatic to see our first observation of neutrino oscillations,” said NOvA co-spokesperson Peter Shanahan of the U.S. Department of Energy’s Fermi National Accelerator Laboratory. “For all the people who worked over the course of a decade on the designing, building, commissioning and operating this experiment, it’s beyond gratifying.”
The experiment’s particle detector is massive. It stands 50 feet tall, 50 feet wide and 200 feet long. Oh, and it’s detecting neutrinos fired from 500 miles away from where it sits in Ash River, Minnesota. Check out a time lapse of its construction below.
Here’s how the experiment works.
A neutrino beam is generated at the Fermilab near Chicago, Illinois. An underground near detector measures the beam’s composition right before it leaves Fermilab site. After that, it takes a 500-mile journey straight through the Earth to the massive detector in Minnesota. Along the way, the neutrinos are oscillating (or changing types).
How do the scientists know the neutrinos were oscillating? They figured if oscillations did not occur, 201 muon neutrinos would arrive at the detector in Minnesota. The detector saw 33. Fermilab scientists could also determine if oscillations were occurring by looking at the number of electron neutrinos. If there were no oscillations, just one electron neutrino was expected. Six electron neutrinos were detected.
NOvA co-spokesperson Mark Messier touched on what makes the NOvA experiment special compared to similar experiments around the world.
“One of the reasons we’ve made such excellent progress is the impressive Fermilab neutrino beam and accelerator team,” said Messier. “Having a beam of that power running so efficiently gives us a real competitive edge and allows us to gather data quickly.”
The NOvA experiment will gather data for at least six years. Armed with this data, scientists hope to better understand neutrinos’ hierarchy and determine if they are connected at all to the Higgs boson.
The data could even help scientists answer a fundamental question about our universe. I’ll let the official website explain:
If the NOvA collaboration discovers that muon antineutrinos oscillate at a different rate than muon neutrinos, they will know the symmetry between the neutrinos and antineutrinos is broken. This could be a clue to why the universe has more matter than antimatter – the reason we exist.
“We’re glad that the detectors are functioning beautifully and providing quality data that will expand our understanding of the subatomic realm,” says Fermilab Director Nigel Lockyer.