# How the experimental mass of neutrino is caluclated as it wont intereact with any type of matter?

Jan 26, 2018

I don’t think it is that the neutrinos ‘won’t interact’ but rather that the interaction is unlikely, however in quantum physics anything not forbidden is essential.

#### Explanation:

This is a (bit of a misquote of Richard Feynman and) quite hard to get your head around, but there are several interactions involving the neutrino that might allow some idea of it’s mass, all involving the weak force.

As the boson (force carrying particle) for these interactions is so massive (all three types are around 80 times the mass of a proton, or millions of times the mass, i.e. energy of the lightest neutrino) it is extremely unlikely to occur. In effect the neutrino has to “borrow” the energy.

The problem is that the higher the amount of energy “borrowed”, the less time it can be “borrowed” for. (This is another formulation of Heisenburg’s famous uncertainty principle, that $\Delta E \times \Delta t > \frac{h}{2 \pi}$ see here for the principles)

In effect the neutrino interacts with another particle in all our experiments and from conservation laws (momentum, energy etc.) the incoming mass can be determined (or at least bounds placed on the upper and lower limits.) The situation is further complicated by neutrino mixing ... but I’ll leave that for another question.

The current best attempts at neutrino observations involve either:

1. (very) large tanks of “heavy” water i.e. enriched with deuterium - see here

2. (very, very) large volumes of ice in Antarctica - see here

3. Or even (large) vats of chlorine rich fluid - see here

In all 3 cases the large volumes involved increase the chances of successful detection, explaining why the ice cube experimental facility (option 2 above) has been so successful.