NOvA sheds new light on how neutrinos behave

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August 8, 2016 – a respected ICHEP international conference was held in Chicago, USA, where scientists from the NovA international experiment published new, very interesting results which may help us better understand the behaviour of neutrinos. The analysis of new measurements has suggested that the correlation between flavour and neutrino mass states might be more complex than we previously assumed.

Neutrinos have been detected in three variants, called "flavours" – as muon neutrinos, tau neutrinos and electron neutrinos. They also exist in three so-called mass states, which, however, may not correspond directly to the flavours. The relationship between these states is governed by a complex process of the so-called neutrino mixing. We have not fully deciphered this process yet but the more we understand the relationships between the states of flavour and the mass states, the better we understand these mysterious particles.

At the ICHEP Particle Physics International Conference held in Chicago, the scientists from the NovA experiment presented a proof of the so-called non-maximal mixing, where one of three mass states does not contain the same admixture of muon and tau flavour as we assumed. This preliminary result of the NovA experiment has been the first sign of this phenomenon at the third mass state.

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An illustration of the three neutrino mass states and the three flavours that make them up (electron, muon and tau), as they were previously thought to mix. NOvA’s new result shows that the third mass state may not have equal amounts of muon (yellow jellybeans) and tau (blue jellybeans) flavours. Image: Fermilab/Sandbox Studios.

The NOvA experiment, managed by Fermilab near Chicago, has measured neutrino data since February 2014. NOvA has used the world's most intense muon neutrino beam that travels 810 km throughout the Earth's crust between Fermilab and a giant remote detector situated at the northern state border of Minnesota. NOvA was designed to investigate neutrino oscillations, the phenomenon by which these particles „flip“ flavors while in transit.

Using oscillations, NOvA has studied the basic properties of neutrinos for two years now. NOvA detectors can detect both muon and electron neutrinos. The detectors are also able to analyze the exact number of muon neutrinos that have travelled throughout the Earth's crust, and the number of electron neutrinos that have appeared in the beam during the transit.

The measured data have also shown that the so-called third mass state has either more muon flavor than that of tau, or vice versa. The NOvA experiment has not collected enough measurements yet to be able to declare this result as a full-fledged discovery of non-maximal mixing but if the measured trend persists, the scientists expect to have enough data to definitively unravel this mystery in the upcoming years.

"NOvA is just getting started," says Gregory Pawloski from the University of Minnesota, one of the scientists who worked on this result. "The sample of the measured data is only one-sixth of the planned total data amount, and it will be exciting to see if this intriguing hint develops into a discovery."

NOvA will be recording further data with neutrino and antineutrino beam for a few more years. With both tuned detectors and the neutrino beam from Fermilab at its full power, the NOvA experiment is well positioned to also unravel other mysteries in the world of neutrinos.

NOvA experiment has also involved Czech scientists from the FJFI ČVUT, FZÚ AV ČR and MFF UK.

Fermilab is America’s premier national laboratory for particle physics research. Fermilab is located near Chicago, Illinois, and operates, among other things, one of the biggest particle accelerators. Additional information is available at https://www-nova.fnal.gov(link is external). The Fermilab website features the presentation of the aforementioned result (link is external) and the English version of the press release (link is external).

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