Neutral Current - Neutrons and Neutrinos

[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]<br /> 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?<br /> <br /> 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...<br /> <br /> Can someone help?<br /> Thanks![/tex]

 

[Norman]

Re Bubble Chamber:

Gargamelle was a giant particle detector at CERN, designed mostly for the detection of neutrinos. Gargamelle was a bubble chamber that held nearly 12 cubic meters of freon (CF3Br). It operated for many years at the CERN PS and SPS.

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

 

[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.

 

[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...

 

[marlon]

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).

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

 

[Meir Achuz]

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