NOvA

Neutrinos are fundamental particles of the Standard Model. They come in three flavours: electron, muon, and tau. Since the 1990s, it has been known that neutrinos change flavour as they travel from one place to another. The discovery of this groundbreaking phenomenon earned the Nobel Prize in Physics in 2015. Although we have known about this for some time, studying it in detail is no easy task. This is because neutrinos interact extremely rarely, which is why they are often called the “ghost” particles. They have an exceptionally small mass (as far as we know, their mass is at most 1 million times smaller than that of an electron), and they lack electric charge or colour, a property related to the binding of protons and neutrons in the nucleus. Neutrinos mainly interact via the weak force. This allows them to travel very long distances undisturbed, and to study them, we need to use intense sources of neutrinos or very large detectors.

NOvA is a world-leading neutrino oscillation experiment based in the US. An intense beam of muon neutrinos is produced at the iconic Fermilab, near Chicago, Illinois. A near detector accurately measures the neutrinos produced, and a far detector, located 810 km away in Ash River, Minnesota, detects the neutrino flavours that arrive there. In this way, NOvA studies neutrino oscillations. NOvA is capable of running these types of measurements with both neutrinos and their antimatter counterparts, antineutrinos.

Studying the differences between neutrinos and antineutrinos, and between matter and antimatter, can offer clues about why the universe developed as it did. As far as we know, the Big Bang produced equal amounts of matter and antimatter. However, when we look at the universe today, we see it is overwhelmingly dominated by matter, which raises a major question: where did all the antimatter go? We believe that neutrinos and antineutrinos may hold the key to solving this mystery, and the NOvA experiment is working to find out.

NOvA at Imperial

Imperial plays a central role in NOvA, with one of our academics serving as the overall Analysis Coordinator of the experiment, overseeing the development of all physics analyses. The focus of the Imperial NOvA group is on both neutrino interaction and neutrino oscillation measurements. As neutrinos cannot be directly observed, measurements of neutrino oscillations depend on our understanding of neutrino interactions. The NOvA near detector observes millions of neutrinos and antineutrinos, providing an ideal environment for studying neutrino interactions, which our group leads. On the neutrino oscillation side, the Imperial group is heavily involved in developing the extrapolation technique, which exploits the similar technologies of the near and far detectors to accurately predict the neutrino spectra at the far detector and measure neutrino oscillation parameters. Finally, Imperial leads the development of both traditional and machine learning algorithms for reconstructing neutrino events, with a particular focus on the attention mechanism and the interpretability of machine learning methods. 

People involved

Group Members: Alex Booth, Linda Cremonesi