The NOvA neutrino experiment has produced stunning results — detecting oscillations of the elusive subatomic particles 500 miles from the location where they were produced. Cosmic rays, generated in outer space, have effects similar to neutrinos. Investigators have sorted through millions of cosmic ray detection events to identify the ultra-rare echoes of neutrinos.
The purpose of the NOvA experiment – which stands for NuMI Off-Axis Electron Neutrino Appearance – is to learn more about the mysterious particles, which physicists have strove to understand for more than 80 years. The detector in the experiment is massive — measuring 50 feet high, 50 feet wide, and 200 feet in length.
Investigators hope their study will also assist physicists in gaining insight into the behavior of the ghostly particle. Little is known about these uncharged particles, which only rarely interact with matter — making them difficult to measure.
"People are ecstatic to see our first observation of neutrino oscillations," said NOvA spokesperson Peter Shanahan from the 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."
Neutrinos are known to exist in three different states, known as "flavors." These are electron, tau and muon. As neutrinos travel, they oscillate between the three different states.
In this experiment, trillions of neutrinos were generated every second at Fermilab and recorded at the source prior to embarking on their trip. They traveled 500 miles underground between the source and detector, changing their flavors during the journey.
"We make a beam of muon-type neutrinos at Fermilab, and then we detect those at Ash River, Minnesota," said Patricia Vahle, associate professor of physics at William & Mary.
"We are looking for muon-type neutrinos to change into electron-type neutrinos," she continued. "We also look for those muon neutrinos to just disappear, or really change into any type of neutrino."
The existence of neutrinos was first proposed in 1930 by physicist Wolfgang Pauli, to explain details of beta decay — in which neutrons decay into protons and electrons. Of the four known forces in nature, they are not affected by either electromagnetism or the strong force, which binds protons and neutrons together in the nucleus of atoms. Gravitation is extremely weak on subatomic particles, and the weak force – responsible for beta radiation – only works at extremely small scales.
This lack of interaction makes the particles exceptionally difficult to detect and measure.
On the rare occasion when a neutrino alters an atom in the detector, the act gives off distinctive light and produces certain particles, cluing investigators in to the flavor of neutrino they detected.