Context: The study of neutrinos is an area of immense current interest among particle physicists and astrophysicists. NOvA is an experiment designed to determine the role of neutrinos in the evolution of the cosmos.
Neutrinos
- Neutrinos belong to a group of fundamental particles called leptons in the Standard Model. They have no electric charge and very little mass (nearly massless).
- They are the second-most abundant particles after photons (particles of light) and the most abundant among particles that make up matter.
- They very rarely interact with matter and that is why they are called “ghost particles”. This means they can travel through vast distances, including entire planets, almost undetected.
- There are three main types of neutrinos: Electron neutrino, Muon neutrino and Tau neutrino. These particles are produced when particles called leptons interact with matter.
- For example, when a type of lepton called a muon interacts with matter, the interaction produces a muon-neutrino.
- The same goes for electrons (electron-neutrino) and tauons (tau-neutrino).
- Source of Neutrinos: Stars, Supernovae, Galaxies, Nuclear reactions.
NOvA experiment:
- The NOvA (NuMI Off-axis νe Appearance) experiment is a prominent neutrino experiment designed to study neutrino oscillations and properties.
- NOvA is specifically designed to observe the transformation of muon neutrinos into electron neutrinos as they travel over a long distance. To achieve this, the experiment utilises two detectors located in the US:
- Near Detector: Located at Fermilab, Illinois, this detector studies the neutrino beam before it undergoes significant oscillation.
- Far Detector: Situated in northern Minnesota, approximately 810 kilometres from the near detector, this detector observes the neutrino beam after it has travelled a long distance and potentially oscillated.
By comparing the neutrino composition at both detectors, scientists can measure the oscillation rate and gather valuable information about neutrino properties.
- Timeline: The NOvA experiment began data collection in 2014 and is currently ongoing.
Quest for three important questions:
The NOvA experiment is designed to answer three fundamental questions in neutrino physics:
Can we observe the oscillation of muon neutrinos to electron neutrinos?
- Neutrinos come in three varieties: muon neutrinos, electron neutrinos and tau neutrinos. Neutrinos can oscillate or change from one type to another, for example, oscillations of muon neutrinos to tau neutrinos. But scientists have not seen muon neutrinos oscillating into electron neutrinos.
- So, the aim is to understand the unknown factors that govern neutrino oscillations that would significantly improve our understanding of how the universe is constituted.
What is the ordering of the neutrino masses?
- Masses of neutrinos are about a million times lighter than the masses of other particles in the Standard Model of physics.
- However, the masses of the different neutrino types and their mass hierarchy (which kind of neutrino is the lightest and which is the heaviest) is not yet known, as of now. Presently, it is believed that neutrinos get their masses through a different process than the other particles.
- Knowledge of the mass hierarchy also will help answer the question of whether neutrinos are their own antiparticles. Particles and antiparticles have opposite charges. Because neutrinos have no electric charge, it is possible that neutrinos and antineutrinos are fundamentally the same.
What is the symmetry between matter and antimatter?
- Physicists theorise that the big bang created equal amounts of matter and antimatter. When corresponding particles of matter and antimatter meet, they annihilate one another. But presently we observe a matter-dominated universe (this is called Charge-Parity violation). So, it appears that at some point, matter and antimatter behaved differently from one another.
- In order to advance the theory that neutrinos tipped the balance between matter and antimatter, neutrino physicists need to observe Charge-Parity violation in action.
- If the NOvA collaboration discovers that muon antineutrinos oscillate at a different rate than muon neutrinos, they will know the symmetry between the neutrinos and antineutrinos is broken. This could be a clue to why the universe has more matter than antimatter – the reason we exist.