# Neutral Current - Neutrons and Neutrinos

1. Jul 19, 2007

### Ahmes

Hi,
We were told in a very-elementary elementary particles course, that a neutral current event was first observed in the following process:
$$\bar{\nu}_\mu + n \longrightarrow \bar{\nu}_\mu + X$$
were X is "something other than muon" (n was a neutron).

I thought about it, and I don't know how X can be something other than a n, a neutron. The interaction between the neutrino and one of the neutron's quark is second order and flavor conserving, so only the momentum changes and not the particle identity.

Yet, I've searched the internet and found that it can also be:
[tex]X=n + \pi^0[/itex]
Where did the pion come from? there should be a photon or a gluon involved if it is to appear from the vacuum. How will the correct diagram look like? And what other things could X be?

And maybe even a more important question - the experiment was said to be done inside of a bubble chamber - BUT WE CAN ONLY SEE CHARGED PARTICLES THERE, NOT NEUTRONS, NEUTRINOS & NEUTRAL PIONS...

Can someone help?
Thanks!

Last edited: Jul 19, 2007
2. Jul 19, 2007

### Norman

Re Bubble Chamber:
There must be energy put into the system for the pion to be there.

A really elementary introduction to the neutral current is given here at hyperphysics:
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neucur.html

3. Jul 19, 2007

### Meir Achuz

Pions interact strongly with nucleons, so often if you hit a nucleon, a pion will be produced. The struck neutron could have produced a proton and a pi-, each of which would be seen in a bubble chamber.

4. Jul 19, 2007

### Ahmes

OK, the process is detectable if the resultant particles are charged. Let's say they really are a pi- and a proton.

u ----->---- u
d ----->---- d
000000000-->-- u
gluon? ---<
000000000--<-- ubar
d ----->---- d
00000|
00000|Z
00000|
ν ----->---- ν

(Don't notice the white zeros - they are just for alignment)

If that is the diagram - then there's still the gluon or photon that comes from nowhere...

5. Jul 20, 2007

### marlon

Hey,

I refer you to a post from our Elementary Particles Presented thread in which you will find ALL the necessary information you are looking for. Click on the links in the end of the page !

regards
marlon

6. Jul 20, 2007

### Meir Achuz

The first step is nu+n-->nu_+n.
Then n-->p+ pi. Anytime you hit a nucleon it can shake off pions.