NOvA experiment sees strong evidence for antineutrino oscillation

June 4, 2018, Fermi National Accelerator Laboratory
This display shows, from two perspectives, an electron antineutrino appearance candidate in the NOvA far detector. Credit: Evan Niner/NOvA collaboration

For more than three years, scientists on the NOvA collaboration have been observing particles called neutrinos as they oscillate from one type to another over a distance of 500 miles. Now, in a new result unveiled today at the Neutrino 2018 conference in Heidelberg, Germany, the collaboration has announced its first results using antineutrinos, and has seen strong evidence of muon antineutrinos oscillating into electron antineutrinos over long distances, a phenomenon that has never been unambiguously observed.

NOvA, based at the U.S. Department of Energy's Fermi National Accelerator Laboratory, is the world's longest-baseline neutrino experiment. Its purpose is to discover more about , ghostly yet abundant particles that travel through matter mostly without leaving a trace. The experiment's long-term goal is to look for similarities and differences in how neutrinos and antineutrinos change from one type—in this case, muon—into one of the other two types, electron or tau. Precisely measuring this change in both neutrinos and antineutrinos, and then comparing them, will help scientists unlock the secrets that these particles hold about how the universe operates.

NOvA uses two large particle detectors—a smaller one at Fermilab in Illinois and a much larger one 500 miles away in northern Minnesota—to study a beam of particles generated by Fermilab's accelerator complex and sent through Earth, with no tunnel required.

The new result is drawn from NOvA's first run with antineutrinos, the antimatter counterpart to neutrinos. NOvA began studying antineutrinos in February 2017. Fermilab's accelerators create a beam of (or muon antineutrinos), and NOvA's far detector is specifically designed to see those particles changing into electron neutrinos (or electron antineutrinos) on their journey.

If antineutrinos did not oscillate from muon type to electron type, scientists would have expected to record just five electron antineutrino candidates in the NOvA far detector during this first run. But when they analyzed the data, they found 18, providing strong evidence that antineutrinos undergo this oscillation.

"Antineutrinos are more difficult to make than neutrinos, and they are less likely to interact in our detector," said Fermilab's Peter Shanahan, co-spokesperson of the NOvA collaboration. "This first data set is a fraction of our goal, but the number of oscillation events we see is far greater than we would expect if antineutrinos didn't oscillate from muon type to electron. It demonstrates the impact that Fermilab's high-power particle beam has on our ability to study neutrinos and antineutrinos."

Although antineutrinos are known to oscillate, the change into electron antineutrinos over has not yet been definitively observed. The T2K experiment, located in Japan, announced that it had observed hints of this phenomenon in 2017. The NOvA and T2K collaborations are working toward a combined analysis of their data in the coming years.

"With this first result using antineutrinos, NOvA has moved into the next phase of its scientific program," said Associate Director for High Energy Physics at the Department of Energy Office of Science Jim Siegrist. "I'm pleased to see this important experiment continuing to tell us more about these fascinating particles."

NOvA's new result accompanies an improvement to its methods of analysis, leading to a more precise measurement of its neutrino data. From 2014 to 2017, NOvA saw 58 candidates for interactions from muon neutrinos changing into electron neutrinos, and scientists are using this data to move closer to unraveling some of the knottiest mysteries of these elusive .

The key to NOvA's science program is comparing the rate at which electron neutrinos appear in the far detector with the rate that electron antineutrinos appear. A precise measurement of those differences will allow NOvA to achieve one of its main science goals: to determine which of the three types of neutrinos is the heaviest and which the lightest.

Neutrinos have been shown to have mass, but scientists have not been able to directly measure that mass. However, with enough data, they can determine the relative masses of the three, a puzzle called the mass ordering. NOvA is working toward a definitive answer to this question. Scientists on the experiment will continue studying antineutrinos through 2019 and, over the following years, will eventually collect equal amounts of data from neutrinos and antineutrinos.

"This first data set from antineutrinos is a just a start to what promises to be an exciting run," said NOvA co-spokesperson Tricia Vahle of William & Mary. "It's early days, but NOvA is already giving us new insights into the many mysteries of neutrinos and antineutrinos."

Explore further: NOvA shines new light on how neutrinos behave

More information: For more information on neutrinos and neutrino research, please visit neutrinos.fnal.gov

Related Stories

The secret to measuring an antineutrino's energy

May 17, 2018

The MINERvA collaboration analyzed data from the interactions of an antineutrino—the antimatter partner of a neutrino—with a nucleus. They were surprised to find evidence that antineutrinos interacted with pairs of particles ...

PROSPECTing for antineutrinos

May 21, 2018

The Precision Reactor Oscillation and Spectrum Experiment (PROSPECT) has completed the installation of a novel antineutrino detector that will probe the possible existence of a new form of matter.

Recommended for you

Quantum computers tackle big data with machine learning

October 15, 2018

Every two seconds, sensors measuring the United States' electrical grid collect 3 petabytes of data – the equivalent of 3 million gigabytes. Data analysis on that scale is a challenge when crucial information is stored ...

Researchers report innovative optical tissue imaging method

October 15, 2018

A UK-wide research team, led by the University of St Andrews, has developed an innovative new way to optically image through tissue, which could allow for a more detailed understanding and diagnosis of the early stages of ...

8 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

billpress11
not rated yet Jun 04, 2018
Quote from article: "NOvA uses two large particle detectors—a smaller one at Fermilab in Illinois and a much larger one 500 miles away in northern Minnesota—to study a beam of particles generated by Fermilab's accelerator complex and sent through Earth, with no tunnel required.:

It would be interesting to see if the result would be the same over 500 miles of space.
jonesdave
3.2 / 5 (9) Jun 04, 2018
It would be interesting to see if the result would be the same over 500 miles of space.


Why wouldn't it be?
antialias_physorg
4.5 / 5 (8) Jun 04, 2018
It would be interesting to see if the result would be the same over 500 miles of space.

Neutrino oscillation probability is a function of distance and the neutrino's energy. The amount of detections is very low (since neutrinos pass through most anything - which includes a detector). So you want to build the detector far away from the source in order to maximize the chance that an oscillation occurred.

You could build the detector very close but that would mean you'd need a lot more detection events in order to reach statistical significance (or you'd need a lot larger detector).

To boot these detectors are built way underground to shield them from any kind of cosmic radiation in order to minimize false positives (i.e. down mountains and mines) which are not the usual locations where you build the emitters.

(Cue theme for mad scientist volcano lab)
granville583762
4 / 5 (4) Jun 09, 2018
Neutrino's change flavour and chirality in flight

It has been known for some time neutrino's change flavour in flight at the speed of light, a constant source of consternation on physics-world due to a particle having to drop below light speed to change flavour which it evidently remains at light speed and simply changes flavour as an energy level.
The anti-flavour neutrino's distinguishing features as having no electric field are their chirality, anti-flavour have right handed spin.

It comes as no surprise the neutrinos ability to to change flavour in flight extends to their chirality.
Chirality; the other main consternation point concerning an anti-particles distinguishing feature on physics-world as what constituents the difference between a particle anti-particle which now comes down to chirality.
ZoeBell
Jun 09, 2018
This comment has been removed by a moderator.
ZoeBell
Jun 09, 2018
This comment has been removed by a moderator.
RealityCheck
1 / 5 (5) Jun 09, 2018
The ambient 'cosmic Neutrino background' may play a part in the so-called Neutrino 'flavor' oscillations. That is, because of the 'wave-particle duality' of such 'objects' as Neutrinos/Anti-Neutrinos, it means that they too are subject to Constructive/Destructive Interference (just as Photonic wave-particles are).

But even more than that aspect, is the apparent fact that the Neutrino 'structure' is more 'complex' than the Photonic 'plane wave' type structure; then Neutrinos' in-flight orientational 'rotations' and mass 'increases/decreases' my be due to interaction between 'locally sourced' and 'ambient cosmic background Neutrinos?

Hence in-flight constructive/destructive interferences and re-orientations may account for the 'oscillation' observations?

Just a thought. :)

Has anyone ever considered and/or tested for this aspect/possibility before?

If anyone has any info on such being done before, can you please link to same if you have the time. Thanks. :)
torbjorn_b_g_larsson
3.7 / 5 (3) Jun 12, 2018
It has been known for some time neutrino's change flavour in flight at the speed of light, a constant source of consternation on physics-world due to a particle having to drop below light speed to change flavour which it evidently remains at light speed and simply changes flavour as an energy level.


There was no consternation here. The flavor changes are due to oscillations between flavor superpositions (in turn allowed by neutrino mass); no energy is changed obviously (conserved momentum) or you could extract energy (differences) out of the vacuum.

It was unexpected though.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.