Why neutrinos?
Particle physics has been very successful in creating the Standard Model, a theoretical framework that describes many particle physics phenomena. However, major discoveries such as the evidence for dark matter and the observation of neutrino mass have shown that the Standard Model is incomplete. These findings strongly suggest that new physics discoveries beyond the Standard Model await us.
Neutrinos could provide the path to unveiling these hidden physics phenomena. In particular, physicists hope that neutrinos will shed light on these questions:
- Why is the universe as we know it made of matter, with no antimatter present?
- What is the origin of this matter-antimatter asymmetry, also known as CP violation?
- Are neutrinos connected to the matter-antimatter asymmetry, and if so, how?
- If neutrinos exhibit CP violation, is it related to the CP violation observed in quark interactions?
- Are neutrinos their own antiparticles?
- What role did neutrinos play in the evolution of the universe?
Physicists have discovered three types of neutrinos so far: electron neutrinos, muon neutrinos and tau neutrinos. Although neutrinos are among the most abundant particles in the universe, they rarely interact with other matter. Hence, they are often referred to as ghost particles.
"For every electron, for every proton, for every neutron, there are about a billion neutrinos... every second there are 100 trillion neutrinos from the sun passing through each person," says Fermilab theorist Boris Kayser. "It's the neutrinos and photons, particles that make up light beams, that are by far the most abundant particles in the universe."
Kayser further explains that a recent theory has developed, which is that the neutrinos may have something very important to do with how the universe came to be dominated by matter and have no antimatter. "Life is possible only because there is no antimatter around. When matter and antimatter meet, they annihilate each other."
By generating huge numbers of neutrinos using high-intensity accelerators and by building large detectors that increase the chance of neutrino observation, physicists can study these mysterious particles and learn more about their role in the universe. The proposed Long-Baseline Neutrino Experiment will give physicists the chance to push the door wide open to search for physics beyond the Standard Model and allow them to make exciting discoveries at the Intensity Frontier.
Credit: Hitoshi Murayama
Further reading:
For an excellent introduction to the neutrino physics opportunities presented by the proposed Deep Underground Science and Engineering Laboratory (DUSEL, no longer a funded entity), read this chapter in the report Deep Science, published by the National Science Foundation.
Details on the scientific questions surrounding neutrinos and their properties and interactions are given in this summary by Boris Kayser and Stephen Parke, members of the Fermilab theory group.