34 08 June 2012 11:43PM

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Comment author: 17 June 2012 08:18:59AM 3 points [-]

What happens when an antineutron interacts with a proton?

Comment author: 17 June 2012 11:17:25AM *  4 points [-]

There are various possibilities depending on the energy of the particles.

An antineutron has valence quarks $\bar{u}$, $\bar{d}$, $\bar{d}$. A proton has valence quarks u, u, d. There are two quark-antiquark pairs here: u + $\bar{u}$ and d + $\bar{d}$. In the simplest case, these annihilate electromagnetically: each pair produces two photons. The leftover u + $\bar{d}$ becomes a positively-charged pion.

The pi+ will most often decay to an antimuon + muon neutrino, and the antimuon will most often decay to a positron + electron neutrino + muon antineutrino. (It should be noted that muons have a relatively long lifetime, so the antimuon is likely to travel a long distance before decaying, depending on its energy. The pi+ decays much more quickly.)

There are many other paths the interaction can take, though. The quark-antiquark pairs can interact through the strong force, producing more hadrons. They can also interact through the weak force, producing other hadrons or leptons. And, of course, there are different alternative decay paths for the annihilation products that will occur in some fraction of events. As the energy of the initial particles increases, more final states become available. Energy can be converted to mass, so more energy means heavier products are allowed.

Edit: thanks to wedrifid for the reminder of LaTeX image embedding.

Comment author: 17 June 2012 01:57:32PM *  3 points [-]

An antineutron has valence quarks u¯, d¯, d¯. (The bar should really be directly above the letter to indicate antiparticles, but Markdown does not have an overline syntax as far as I know.)

Piece of cake:

$\bar{u}, \bar{d}, \bar{d}$

![](http://www.codecogs.com/png.latex?\\bar\{u\},%20\\bar\{d\},%20\\bar\{d\})

Comment author: 17 June 2012 11:10:11PM *  3 points [-]

Another approach is to use actual combining overlines U+0305: u̅, d̅, d̅. This requires no markup or external server support; however, these Unicode characters are not universally supported and some readers may see a letter followed by an overline or a no-symbol-available mark.

If you wish to type this and other Unicode symbols on a Mac, you may be interested in my mathematical keyboard layout.

Comment author: 17 June 2012 04:16:39PM 2 points [-]

Very complicated things.

Both the antineutron and the proton are soups of gluons and virtual quarks of all kinds surrounding the three valence quarks Dreaded_Anomaly mentions; all of which interact by the strong force. The result is exceedingly intractable. Almost anything that doesn't actually violate a conservation law can come out of this collision. The most common case, nonetheless, is pions - lots of pions.

This is also the most common outcome from neutron-proton and neutron-antiproton collisions; the underlying quark interactions aren't all that different.

Comment author: 17 June 2012 09:19:48AM *  0 points [-]

What happens when an antineutron interacts with a proton?

Good question.

I'm going to tender the guess that you get a kaboom (energy release equivalent to the mass of two protons) and a left over positron and neutrino spat out kind of fast.