Antimatter questions

glass · Post by **glass** » 2007-01-31 09:45am

We all know that matter and antimatter annihilate each other on contact, right, but a question occurred to me the other day: Do particles have to annihilate with their own antiparticle? And if so, how do non-matching particle interact (if at all)?

IOW: What happens if you fire a beam of antineutrons into a cloud of (non-heavy) hydrogen gas?

glass.

Velthuijsen · Post by **Velthuijsen** » 2007-01-31 11:28am

They annihilate each other. The reaction is on quark level, recombining the remaining quarks into other particles

An anti-neutron consists of one anti-up quark and two anti-down quarks.
A proton consists of two up quarks and one down quark.
The anti-down quark and up quark recombine into a pion.

Kuroneko · Post by **Kuroneko** » 2007-01-31 11:50am

Antineutrons should be unstable, decaying into antiprotons and positrons (neutrons have a half-life on the order of minutes), so it would be rather difficult for there to be any appreciable amount of them without having them decay into anti-hydrogen plasma.

If you look at the quark composition, the only mismatch is up with anti-down, which yields a pi+ meson, which likely decay into a positron (eventually; other particles first); the rest will probably follow pi0 -> 2gamma. The positrons and the hydrogen's electrons may annihilate, but overall the process will probably be very 'dirty'. Other decay modes are possible.

glass · Post by **glass** » 2007-02-05 06:28am

Thanks guys, for taking the time to educate the scientifically semi-literate amongst us. Sorry it's taken me days to come back to this thread: I haven't been well. I did think about quarks after I posted the question, but I didn't have a chance to come back to it until now. Anyway, looks like I wasn't totally off base; there is hope for me yet.

Kuroneko wrote:Antineutrons should be unstable, decaying into antiprotons and positrons (neutrons have a half-life on the order of minutes), so it would be rather difficult for there to be any appreciable amount of them without having them decay into anti-hydrogen plasma.

I didn't know that. They really should have taught me some of this stuff in A-level Physics, rather than bloody logic gates for the seventh time!

glass.

Gil Hamilton · Post by **Gil Hamilton** » 2007-02-05 08:49am

Not to poo-poo anti-matter physics, but logic gates are alot more useful.

glass · Post by **glass** » 2007-02-05 10:19am

Gil Hamilton wrote:Not to poo-poo anti-matter physics, but logic gates are alot more useful.

Possibly true, but having studied them in the second year or secondary school, and the third, and again (twice) for GCSE, and then again (twice) for A-level, with no new information until I studied them yet again at University, it all got a bit much.

glass.

Fingolfin_Noldor · Post by **Fingolfin_Noldor** » 2007-02-05 05:37pm

Gil Hamilton wrote:Not to poo-poo anti-matter physics, but logic gates are alot more useful.

A Quantum logic gate is a infinitely more useful

The only thing is to get it working first and let the EECS guys go drool over it.

Spin Echo · Post by **Spin Echo** » 2007-02-05 06:10pm

Fingolfin_Noldor wrote:
Gil Hamilton wrote:Not to poo-poo anti-matter physics, but logic gates are alot more useful.
A Quantum logic gate is a infinitely more useful The only thing is to get it working first and let the EECS guys go drool over it.

Well, you do get working quantum logic gates. It's getting enough of them working together that's the tricky bit. Last I heard they only had about 7 qubits, though that was in the liquid state. As for antimatter, I've never heard of it being used for quantum computing, but my knowledge in the area is limited.

drachefly · Post by **drachefly** » 2007-02-06 01:38pm

Also, it may be important to note that antimatter does not need to annihilate immediately with its matter counterpart. It happens pretty quickly, though.

Kuroneko: it's not so bad if you're making the antineutrons right before shooting them, e.g. by decay of a heavy anti-atom or some cleverly tuned process not needing antimatter feedstock. If the relativistically dilated time of flight is small compared to decay time, decay should be insignificant. If this hydrogen gas target is really big - a nebula, say, it's going to be significant.

Master of Cards · Post by **Master of Cards** » 2007-02-06 07:17pm

Spin Echo wrote:
Fingolfin_Noldor wrote:
Gil Hamilton wrote:Not to poo-poo anti-matter physics, but logic gates are alot more useful.
A Quantum logic gate is a infinitely more useful The only thing is to get it working first and let the EECS guys go drool over it.
Well, you do get working quantum logic gates. It's getting enough of them working together that's the tricky bit. Last I heard they only had about 7 qubits, though that was in the liquid state. As for antimatter, I've never heard of it being used for quantum computing, but my knowledge in the area is limited.

Link requires login

Spin Echo · Post by **Spin Echo** » 2007-02-06 10:53pm

Master of Cards wrote:Link requires login

Hmm yes. This one should work better. If we want to discuss quantum logic gates further though, we should start a new topic.