# Neutrinos questions!

1. Sep 30, 2011

### AlfreCabo

I have some questions regarding the recent neutrino´s theories:

1. Neutrinos have or dont have mass? I have heard both postures.
2. I have read that reason for neutrinos go through matter (like in the OPERA experiment from CERN to Grand Sasso) is because they dont have mass. Photons also dont have mass, so why light is stopped by mass such as a wall?
3. << overly speculative topic question deleted by Mentor >>

Thanks!

Alfredo

Last edited by a moderator: Sep 30, 2011
2. Sep 30, 2011

### iRaid

Wondering same questions!

3. Sep 30, 2011

### Staff: Mentor

Your 3rd question involved an overly-speculative topic, so it was deleted. We don't engage in overly speculative discussions at the PF. (Please see the Rules link at the top of the page).

http://www.ps.uci.edu/~superk/neutrino.html

.

4. Oct 1, 2011

### Parlyne

At least two of the three neutrino states must have mass. Otherwise, the neutrino mixings we observe would be impossible.

The reason that neutrinos interact so weakly is simply because they are unaffected by either the electromagnetic force or the strong force (which holds together the quarks in protons and neutrons). All of their interactions are through the weak force which, as it's name suggests, is really quite weak. In fact, it's so weak that particles typically need to get within about $10^{-17}$ meters to feel it. For comparison, the radius of a proton is almost $10^{-15}$ meters.

5. Oct 1, 2011

### Staff: Mentor

You've heard (or read) both postures because the existence of neutrino mass was established only fairly recently, during the last 10-15 years. Before that, physicists generally assumed that neutrinos had zero mass, in the lack of evidence to the contrary, while of course continuing to search for definitive evidence one one way or the other. Old books, articles, Web sites, etc. contain outdated information.

6. Oct 3, 2011

### twofish-quant

They have mass. Books that say otherwise have outdated information since this was only established in 1998.

That's incorrect. The reason neutrinos go through everything is that they don't interact via the strong nuclear force or electromagnetism. They only thing that affects neutrinos is the weak force, and the weak force is weak.....