NOvA experiment is observing neutrino transformations

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Scientists on the NOvA experiment published their first evidence of oscillating neutrinos, confirming that the extraordinary detector built for the project not only functions as planned but is also making great progress toward its goal of a major leap in our understanding of these ghostly particles. This announcement was made at the American Physics Society conference held in Ann Arbor, USA.

Neutrinos – the omnipresent and yet enigmatic particles – travel through common mass as easily as if the mass did not exist. It was exactly owing to their reluctance to interact with any matter which made scientists build a huge detector with a cross-section of 16 x 16 m, the length of 65 m and the weight of 14 000 tons and placed it in the way of a neutrino beam generated at the Fermilab. The detector is located in the distance of 810 km from the source of the neutrino beam. At this source, there is another smaller, 300 ton detector which measures the quality of the beam and the representation of individual neutrino types. From there the beam is passed under the Earth‘s surface to reach a distant detector in Ash River in Minnesota, USA.

Researchers have collected data since Feb 2014 while the construction was still under way. This allowed the testing of all detector systems during the construction and the experiment was fully launched shortly after the construction was complete in November 2014.

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A view across the top of the NOvA far detector in Minnesota.

The NOvA collaboration comprises 210 scientist and engineers from 39 institutions in the United States, Brazil, the Czech Republic, Greece, India, Russia and the United Kingdom. The Czech Republic is represented by research teams from the Czech Technical University (ČVUT), the Institute of Physics of the CAS and Charles University, with the backing of the Ministry of Education of the CR.

Neutrinos are the most abundant massive particles in the universe but are still poorly understood. Today we distinguish three types of neutrinos – electron, muon and tau. They have a non-zero mass, we roughly know the absolute values of the differences in their mass but we do not know which is the heaviest and the lightest. The determination of this hierarchy is one of the goals of the NOvA experiment and, at the same time, an important test for theories about how the neutrino gets its mass. While the famed Higgs boson helps explain how some particles obtain their masses, scientists don‘t know yet if this mechanism is also applicable to neutrinos.

Each second trillions of mainly muon neutrinos are sent from Fermilab to the detector in Minnesota. If the neutrinos did not change during the transit, i.e. did not oscillate, researchers should see signals from 201 muon neutrinos in the collected data. They saw mere 33 however; which is a proof that the muon neutrinos were disappearing – as they transformed into the two other flavours. This is also shown by the fact that 6 interactions of electron neutrinos were observed, although only one interaction had been expected.

Such oscillations were also observed in other experiments with a long oscillating base, such as T2K in Japan or MINOS in Fermilab. NOvA which will be take data for at least six years is seeing nearly equivalent results in a significantly shorter time frame, something that bodes well for the experiment‘s ambitious goal of measuring neutrino properties that have eluded other experiments so far.

One of the reasons for the fast progress is the perfect work of the team who take care of the main accelerator system in Fermilab. This allowed to set a world record by reaching high-energy neutrino of 521 kW, and the laboratory is working on improving the neutrino beam even further for projects such as NOvA and the upcoming Deep Underground Neutrino Experiment (DUNE). Researchers expect to reach 700 kW early next calendar year, tripling the amount of data recorded until summer next year.

At NOvA the measurement of neutrino mass hierarchy is also crucial information for neutrino experiments trying to determine if the neutrino is its own antiparticle.

Like T2K, 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. Soon, scientists will be able to combine the neutrino results obtained by T2K, MINOS and NOvA, yielding more precise answers about scientists’ most pressing neutrino questions


The original of the press release and any related pictures may be found at the following websites:


http://www.fnal.gov/pub/presspass/press_releases/2015/NOvA-Neutrinos-Change-20150807.html,
http://www.fnal.gov/pub/presspass/press_releases/2015/NOvA-Neutrinos-Change-20150806-images.html.
Additional information about the NOvA experiment are available at http://www-nova.fnal.gov.
Interactions recorded by the NOvA experiment may be viewed live at the following website: http://nusoft.fnal.gov/nova/public.

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