Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: CPT ArkAngel on 16/05/2011 01:51:32

Title: Is there any experiment showing anti-neutron without a doubt?
Post by: CPT ArkAngel on 16/05/2011 01:51:32

I am searching a proof of the existence of the anti-neutron but i can't find anything really convincing.

A neutron seen upside down looks like an anti-neutron (looking at its magnetic moment).

Does the anti-neutron beta decay have been observed with its anti-proton and positron?

Title: Is there any experiment showing anti-neutron without a doubt?
Post by: JP on 16/05/2011 05:19:38

It's a tiny neutral particle, so the only practical way to observe it is to find the charged decay products when it collides with something else.  Apparently this has been observed:

http://en.wikipedia.org/wiki/Antineutron

"The antineutron was discovered in proton–proton collisions at the Bevatron (Lawrence Berkeley National Laboratory) by Bruce Cork in 1956, one year after the antiproton was discovered."

Title: Is there any experiment showing anti-neutron without a doubt?
Post by: CPT ArkAngel on 16/05/2011 21:59:33

I know about this, but how they are so sure it is an anti-neutron? Of what i read, it is almost impossible to differentiate anti-neutron from neutron, for now.

http://www.time.com/time/magazine/article/0,9171,810296,00.html

http://en.wikipedia.org/wiki/Neutron-antineutron_annihilation

Title: Is there any experiment showing anti-neutron without a doubt?
Post by: imatfaal on 16/05/2011 23:04:06

Really guessing here - but if the creation is via anti-protons interacting with hydrogen/proton (which is what I gather) then you can through strict book-keeping be certain.  what ever interactions you get - you will have baryon number conservation.  if you are losing anti-protons, and it's not through annihilation, then the resultant particles cannot be a pair of neutrons as that would mean that an anti-baryon and a baryon went in yet two baryons emerged.  This is known as a form of the charge exchange reaction if you want to search on it - an anti-proton and a proton go in - and an anti-neutron and a neutron come out. 

Once you have them - you can always just slam them into an iron wall and watch the sparks (well pions i guess) which of course is another sign that they are antiparticles - if they were only neutrons no noticeable reaction would occur.

Title: Is there any experiment showing anti-neutron without a doubt?
Post by: CPT ArkAngel on 16/05/2011 23:20:31

But if the neutron is its own anti-particle and it collides at relativistic speed? Did they succeed to find it at slow speed?

If you search "neutron anomaly or anomalies", you will find many experiments that concluded that the standard model of the neutron is wrong... It does not mean there is no anti-neutron though...

Title: Is there any experiment showing anti-neutron without a doubt?
Post by: imatfaal on 16/05/2011 23:50:14

CPT - not sure what the speeds have to do with the concept of baryons number conservation - or the fact that a large annihilation event is happening.

And can they get slower ones? - seems yes.  I cannot get behind paywall and I need to hit the sack, but have a read of this http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=258948

Title: Is there any experiment showing anti-neutron without a doubt?
Post by: CPT ArkAngel on 17/05/2011 02:08:20

Conservation of momentum is the key. Yes, there is anti-neutrons. 300 MeV/c is a relatively low speed compare to proton and neutron mass. Thx!