NUTRAILS

On the trails of new neutrino properties

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 Obiettivo del progetto (Objective)

'Neutrino masses and mixing are the most tangible evidence for the shortcomings of the Standard Model and finding a more complete theory remains the most challenging task for elementary particle physics. Neutrinos can lead us on the trail to new physics, together with experiments at the LHC, flavor physics and cosmology. The best time for carrying out this project is now. Neutrino physics is more vibrant than ever as a renewed flow of key data has just begun. First evidence that the hitherto unknown value of the third neutrino mixing angle theta(13) is sizeable raises concrete hopes of observing CP-violation in the lepton sector, triggering new ideas for model building. Moreover, the entire neutrino community is intrigued by several experimental anomalies that hint at unexpected neutrino properties. This animated scenery provides an ideal stage for the 'NuTrails' project, having neutrinos as its main actors. Following the trails of these elusive particles to the smallest scales will serve as a formidable guide to new discoveries.

More specifically, this project will focus on two different classes of standard-model extensions. First, signs for new physics originating from heavy mediators at the TeV scale will be studied. Second, manifestations of a new low-energy scale will be sought, hunting for light 'sterile' neutrinos with mass in the eV range. Theoretical questions related to neutrino flavor conversion in the presence of such new properties will be addressed. Furthermore, observable consequences for present and future experiments will be quantified. These results will have far-reaching implications, extending from particle phenomenology to astrophysics and cosmology. Most importantly, the quantitative simulations will decisively influence the next round of experimental strategies.'

Introduzione (Teaser)

By learning more about neutrinos and their properties, physicists seek to complete the standard model picture of the subatomic world. In addition, neutrinos offer a new window to physics beyond the standard model

Descrizione progetto (Article)

Physicists have spent a lot of effort exploring the properties of these mysterious particles. By the end of the last century, they had discovered that neutrinos come in three types or 'flavours': electron, muon and tau. Moreover, neutrinos can switch flavour through a process called oscillation. This surprising fact indicated physics beyond the standard model.

Within the EU-funded project NUTRAILS (On the trails of new neutrino properties), physicists geared up for neutrino studies that will open a window on new physics hidden in the subatomic world. They concentrated their research on standard and non-standard neutrino properties, such as the charge-parity (CP) symmetry violation and the impact of sterile neutrinos.

According to current understanding of the Big Bang, matter and antimatter formed in equal amounts when our Universe was born. If that was the case, every smidgen of matter and antimatter should have annihilated each other as they were made. To explain the predominance of matter, physicists searched to find the right kind of CP symmetry violation.

Previous studies found a difference in the behaviour of quarks and their antiparticles. However, this CP symmetry violation does not explain the overall matter-antimatter imbalance. Exploiting a wealth of neutrino data from experiments around the world, the NUTRAILS project provided the first hint in favour of the CP symmetry violation for neutrinos, particles of the family of leptons.

Additionally, NUTRAILS scientists studied oscillations of neutrinos between the three flavours in search of sterile neutrinos. The existence of this type of neutrinos beyond the three known types, when proven, will have a profound impact on our understanding of the Universe. The new results set limits on the mixing of electrons with sterile neutrinos and on light sterile neutrinos with mass in the sub-eV scale.

The NUTRAILS project has provided ongoing experiments with valuable boundaries for the searched mass range for the fourth possible neutrino state. In addition, the project has pointed out, for the first time, that present and future long-baseline experiments are sensitive to CP symmetry violation induced by the sterile neutrinos.

Overall, the new findings on neutrinos make it clear that it is important to search for other neutral particles that contribute to the matter-antimatter balance of our Universe.