Neutron Anti-Neutron Anihilation

ScienceNerd36

Do Neutrons and anti-Neutrons annihilate? I can't imagine any reason why they would, I just thought I'd check.

Vanadium 50

Yes.

jtbell

Why do you think they wouldn't annihilate?

ScienceNerd36

My logic was: a neurton is it's own anti-particle, and seeing as atomic nuclei can exist the neutrons in the atomic nucleus aren't anihilating each other, hence neutrons shouldn't anihilate anti-neutrons. This logic worked for me because I figured particles only anihilated anti-particles becuase the electric attraction caused them to collide, and seeing as they have equal mass ever single part of the particle collided with another anti-part, which is they there is no mass left, only energy.

Bob_for_short

Neutron is not its own anti-particle. In atomic nuclei there are only neutrons and protons.

ScienceNerd36

Fair enough, thanks for all the help :)

jtbell

The molecules in a gas are electrically neutral, and therefore have no electrical attraction to each other (except for the small van der Waals force when they get really close to each other), but they still collide with each other a lot.

ScienceNerd36

So, what is the force that acts on particles and anti-particles which causes them to annihilate? In other words, what is the force that attracts them to one another?

Bob_for_short

If the particle and its antiparticle are charged, there is an electrostatic interaction (attraction). Normally they annihilate when they are close enough to each other, like an electron and positron in positronium atom. If they are neutral like neutrons, there is still a short-range strong (nuclear) interaction that makes it possible to annihilate and transform into another neutral system.

ScienceNerd36

So it's still a fundamental force acting on the particles, drawing them close together which then allows them to annihlate.

Now I'm off to find out how annihilation works. Any help from you fellas would be much appreciated.

Bob S

If a thermalized anti-neutron were in a tank of liquid hydrogen, would it annihilate with a proton? Protons can exist in a virtual state of a neutron, a positron, and an antineutrino for short times (hbar ~ 6 x 10^-22 sec). Anti-neutrons can also exist in both real and virtual states of an antiproton, a positron, and an antineutrino.
Bob S

Bob_for_short

I do not think so. These virtual transitions are due to the weak interaction. I think some strong-interaction transformations will dominate - the reaction products will be different (mesons?).

Bob S

I agree. As soon as the anti-neutron annihilates, there will be "pionization", with an average of ~ 7 pions (as I recall) in the pion cloud for antiproton annihilation. There will not be two back-to-back 939 MeV gammas (maybe rarely), like in positron annihilation.
Bob S

Bob_for_short

Three pions for sure - the number of quarks is six. The rest depends on excess of energy.

clem

An anti-neutron and a proton would annihilate to pions via the strong interaction. You don't need a neutron.