Ten years into the making, Fermilab’s NOvA experiment has finally yielded results by detecting neutrinos fired from 500 miles away assuring that the experiment works and it will be able to deliver the intended.
The experiment is basically a quest to learn about the abundant yet ghostly particles dubbed neutrinos which flit through ordinary matter as though it weren’t there. Presented at the American Physical Society’s Division of Particles and Fields conference in Ann Arbor, Michigan, US the first results of the experiment prove that the experiment’s massive particle detector actually works.
“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.”
Researchers have been busy collecting data since February 2014 by recording neutrino interactions in the 50 feet tall, 50 feet wide and 200 feet long 14,000-ton far detector in Ash River, Minnesota, while construction was still under way. This allowed the collaboration to gather data while testing systems before starting operations with the complete detector in November 2014, shortly after the experiment was completed on time and under budget. NOvA construction and operations are supported by the DOE Office of Science.
For the uninitiated, neutrinos are said to be the most abundant massive particle in the universe but are still one of the most poorly understood ones. Scientists have been able to find that neutrinos come in three types; however, they don’t know which one is the heaviest and which one is the lightest. This is what researchers intend to do with the NOvA experiment – a litmus test for theories about how the neutrino gets its mass. Researchers will also be trying to see if the neutrino is its own antiparticle.
As for the experiment, the neutrino beam generated at Fermilab passes through an underground near detector where its composition is measured. The beam then travels more than 500 miles straight through the Earth oscillating (or changing types) along the way. About once per second, Fermilab’s accelerator sends trillions of neutrinos to Minnesota, but the elusive neutrinos interact so rarely that only a few will register at the far detector.
When a neutrino bumps into an atom in the NOvA detector, it releases a signature trail of particles and light depending on which type it is: an electron, muon or tau neutrino. The beam originating at Fermilab is made almost entirely of one type — muon neutrinos — and scientists can measure how many of those muon neutrinos disappear over their journey and reappear as electron neutrinos.
For the experiment, results of which were presented at the conference, researchers hypothesized that if oscillations did not occur, they would see 201 muon neutrinos arrive at the NOvA far detector in the data collected; instead, they saw a mere 33, proof that the muon neutrinos were disappearing as they transformed into the two other flavours.
Similarly, if oscillations did not occur, scientists expected to see only one electron neutrino appearance (due to background interactions). But the collaboration saw six such events, evidence that some of the missing muon neutrinos had turned into electron neutrinos.
“One of the reasons we’ve made such excellent progress is the impressive Fermilab neutrino beam and accelerator team,” said NOvA co-spokesperson Mark Messier of Indiana University. “Having a beam of that power running so efficiently gives us a real competitive edge and allows us to gather data quickly.”
NOvA can also run in antineutrino mode, opening a window to see whether neutrinos and antineutrinos are fundamentally different. An asymmetry early in the universe’s history could have tipped the cosmic balance in favor of matter, making the world we see today possible.
“The rapid success of the NOvA team demonstrates a commitment and talent for taking on complex projects to answer the biggest questions in particle physics,” said Fermilab Director Nigel Lockyer. “We’re glad that the detectors are functioning beautifully and providing quality data that will expand our understanding of the subatomic realm.”