Why are Neutrinos Right-Handed ?

So if a Neutrino "spun" in the opposite direction, would we all be living in an "Anti" world? How do we know we aren't ?

Originally posted by woadman
So if a Neutrino "spun" in the opposite direction, would we all be living in an "Anti" world? How do we know we aren't ?

What world is anti and what world is normal is a matter of definition.
Our world is normal by definition, the other is anti.

Originally posted by woadman
So if a Neutrino "spun" in the opposite direction, would we all be living in an "Anti" world? How do we know we aren't ?

If neutrinos were massless then since only the left handed chiral component couples to the weak force right handed neutrinos wouldn't interact in the Standard Model and so were left out. The discovery of neutrino oscillation was explained by neutrinos having a small mass. Mass connects the chiral components of massive particles so there are right handed neutrinos.

Momentarily veering away from the topic of angular momentum to look at linear momentum, is it necessary for an individual neutrino to change speeds (as measured in some inertial frame) as it oscillates through a variety of flavors and hence a variety of masses, in order for linear momentum to be conserved?

Originally posted by Paul Dirac II
Momentarily veering away from the topic of angular momentum to look at linear momentum, is it necessary for an individual neutrino to change speeds (as measured in some inertial frame) as it oscillates through a variety of flavors and hence a variety of masses, in order for linear momentum to be conserved?

Velocity isn't the simple concept in quantum theory that it is in classical physics. These things have masses less than electron volts but energies of the order of MeV's so they travel at close to the speed of light anyway. I think that the difference in time between emission of an electron type neutrino from the Sun and its detection on Earth is longer as a result of oscillation than it would be if there were no oscillation but it did have mass. So in that sense yes I think its speed would drop (although if it was a tau type neutrino on emission then it would arrive sooner). I'm wary of my answer though as the three components of the wavefunction (electron, muon and tau type neutrino) could propagate at different speeds so the type of neutrino at detection could be the determinant of the flight time. I'll sleep on it and post again tomorrow.

Originally posted by DeepThought
Velocity isn't the simple concept in quantum theory that it is in classical physics. These things have masses less than electron volts but energies of the order of MeV's so they travel at close to the speed of light anyway. I think that the difference in time between emission of an electron type neutrino from the Sun and its detection on Earth is longe ...[text shortened]... etection could be the determinant of the flight time. I'll sleep on it and post again tomorrow.

uhh I'm not sure but I seem to remember that a pion is the same as muon if it is neutral ( that is to say, not negative or positive?

Originally posted by woadman
uhh I'm not sure but I seem to remember that a pion is the same as muon if it is neutral ( that is to say, not negative or positive?

Different things. There are three generations of particles. The lowest mass generation has the electron, a corresponding neutrino, and the up and down quarks. The next generation has a muon, like the electron but heavier, and the strange and charmed quarks. The most massive generation and as far as we know there are no others, has a tau (an even heavier electron, about 70% heavier than a proton) and a tau type neutrino, to go along with the top and bottom (aka truth and beauty) quarks.

A pion is a quark anti-quark pair. The pion has one of three charges (+1, 0, -1) depending on which quarks are there. A negatively charged pion will decay into a muon and an anti-neutrino as the most likely decay product (next is an electron and a neutrino). The pion is not the same as a muon but can decay into one. Neutral pions decay into a couple of photons with the highest probability and an electron positron pair with the next highest. They can't decay into a muon anti-muon pair as the mass of a neutral pion is 139MeV/c² and the mass of a muon is 105MeV/c² so there isn't enough energy.

http://en.wikipedia.org/wiki/Pion

Originally posted by DeepThought
Velocity isn't the simple concept in quantum theory that it is in classical physics. These things have masses less than electron volts but energies of the order of MeV's so they travel at close to the speed of light anyway. I think that the difference in time between emission of an electron type neutrino from the Sun and its detection on Earth is longe ...[text shortened]... etection could be the determinant of the flight time. I'll sleep on it and post again tomorrow.

I think it's the latter. If a neutrino starts off as an electron type neutrino and is detected as an electron type neutrino then it will have the same flight time as if neutrino oscillation didn't happen. If it's detected as a muon-type neutrino it will have the flight time that a muon type neutrino of that energy would have if it had been a muon type neutrino all along, and if it's detected as a tau neutrino then its flight time will be the one for a tau. I don't know the emprical status - although since they weren't sure if the things didn't go faster than light for a while it's doubtful to me that they have enough precision to measure this.

That's where Gamma Rays come from....the decayed muons....