Neutrino collision with a proton,neutron or an electron?

[jayaramas]

what happens if a neutrino hits head on with a proton,neutron or an electron?

 

[grzz]

A neutrino is highly non interacting. But there are possibilities for interaction so long as no conservation law is broken.

 

[jetwaterluffy]

From what I remember, a neutrino does interact with the weak force. So if it hits a proton or neutron head on, then it will be affected. An electron is a point particle, so you can't get another point particle, such as a neutrino, to hit "head on" with it in some sense. The electron doesn't interact with the weak force anyway, from what I know, so there would be no effect, except perhaps gravitational forces.

 

[Bill_K]

Several possibilities. Among them:

ν_e + p → n + e⁺

ν_e + e → μ + ν_μ

 

[jayaramas]

so if u calculate number of protons in Earth and still considering that all solar neutrinos pass through it is not justifiable is it?

 

[phinds]

so if u calculate number of protons in Earth and still considering that all solar neutrinos pass through it is not justifiable is it?

I assume you mean it is unlikely, yes? Unlikely is not the same as impossible. It is a valid question.

 

[jayaramas]

what is the reverse process? any way neutrino came from a nuclear reaction, so a fast moving neutrino can hit and attains its position back. why is it not likely?

 

[kurros]

what is the reverse process? any way neutrino came from a nuclear reaction, so a fast moving neutrino can hit and attains its position back. why is it not likely?

Consider
$$n → p + e^{-} + \bar{\nu}_{e}$$
The chances of the products all colliding back together at the same time are negligibly tiny.

but ok fine you could have a slightly different process:
$$p + \bar{\nu}_{e} → n + e^{+}$$
In this case I think the problem is that neutrinos interact very weakly and the scattering has to exceed a minimum threshold energy to happen (since this reaction requires energy input), and this has a very low chance of occurring. i.e. you would need very fast neutrinos indeed to start with, and even then they will hardly interact anyway.

 

[DrDu]

Basically, these inverse decay processes are how neutrinos are detected in neutrino detectors.

 

[bbbeard]

The electron doesn't interact with the weak force anyway, from what I know, so there would be no effect, except perhaps gravitational forces.

Not true. Actually, beta decay is the paradigmatic weak force interaction.

 

[jetwaterluffy]

Not true. Actually, beta decay is the paradigmatic weak force interaction.

Yeah, I worked that out after I had already posted. However, I still can't see how they can "collide".

 

[AdrianTheRock]

Yeah, I worked that out after I had already posted. However, I still can't see how they can "collide".

Think of it as an interaction, rather than a collision.

A particular particle interaction has a measure of reactivity which is termed a cross-section. As the name suggests, this quantity is actually in units of area - it could be expressed in square metres, though the more commonly used unit is the http://en.wikipedia.org/wiki/Barn_(unit)" . But you can loosely think of this as the "target area" that the other particle has to "hit" for an interaction to occur.

An electron and an (anti-)neutrino can combine to form a W^- boson. In any practical scenario, this W^- will be virtual as its mass is far larger than those of the incoming particles, so it will almost immediately decay again, and can usually only decay back into another e and neutrino because any other decay route would produce particles of higher energy. So the end result in this case is simply an elastic collision.

But electrons and (non-anti-)neutrinos can also interact. In this case, the electron could give off a W^- and thereby transform itself into a neutrino, while the W^- is absorbed by the original neutrino and is thus transformed into an electron. Swap ya! (Alternatively, the neutrono could emit a W⁺ which the electron then absorbs, with the same end result.) Again, this is an elastic collision.

The second type of interaction can also take place but with a Z⁰ instead of a W. In this case the electron could interact with either a neutrino or an anti-neutrino. Interactions with Z⁰ do not change the identities of the incoming particles.

These interactions all have extremely small cross-sections - but they do happen. The W interactions are the basis of the http://en.wikipedia.org/wiki/MSW_effect" which has to be taken account of when looking at neutrino oscillations where the neutrinos have traveled through regions containing matter.