The not-so-Elusive Neutrinos

What we know about neutrinos, what do we want to find out, and why do we care?

Super-K data. Image from the t2k site.

Neutrinos are the smallest, neutral particles scientists have observed other than photons. Their name is well chosen. Neutrino means the small, neutral one in Italian. They come in three flavors: the electron, muon and tau neutrino. We know mass differences between flavors and that neutrinos can oscillate between the three available flavors as they travel through space. The probability of measuring a particular flavor for a neutrino varies periodically as the particle propagates.

What we do not know is the actual masses of the neutrinos or if the neutrinos can be their own anti-particle. Some experiments such as the T2K will measure neutrino oscillations more accurately and others such as the Majorana experiment constrain the neutrino mass. The cool thing about neutrinos is that they interact very weakly with other particles and fields.  This is why they come out early from very dense and hot places.  They can carry information from supernovae remnants, the core of the sun or the Galactic center. They provide unique information about objects produced in messy environments such as young neutron stars that we could not study otherwise.

Why have I written this post?
I have attended two seminars on neutrino experiments. We had a speaker from the T2K (Tokai to Kamioka) collaboration and one from the Majorana demonstrator. The message of the talks was largely that while there has been significant progress made, we have the technology to build better experiments and we are building them. Both talks were good, but I wish they had spent a few slides talking about the broader impacts of their research vs. just the details of their results. However, these talks stimulated me to brush up my knowledge of neutrinos and write this post.