# B Matter/antimatter hybrid atomic structures?

#### atracious

Summary
I'm wondering if there is theoretically a combination of matter and antimatter elementary particles that could form something similar to atoms without annihilation occurring or being a likely risk.
I know that direct interaction of opposite chirality(?) particles results in annihilation(eg. proton and antiproton). And I have read that proximity of quark and antiquark, even if in separate subatomic particles, results in at least partial annihilation(eg. Antineutron and proton). But I am curious about obscure combinations of matter and antimatter, and whether they could be stable together to form atoms, or even entire environments.

I am trying to figure based on if all matter nearby was similar,(ie. Earth is almost exclusively matter). So, for example, would it be possible for everything to still form normally if instead of electrons there were only poistrons? Or for example if all down quarks were antiquarks, would they be stable? Or any other combination of elementary particles?

I would prefer to tend slightly more to layman's terms as I am mostly unfamiliar beyond the basic understanding of quarks, antimatter, and the other elementary particles. I would also like to know why certain pairings/groupings couldn't work and what would result, if possible. I am not looking for anything provable by experimentation, just something that under rough hypothetical conditions could work.

I greatly appreciate any and all answers to my queries.

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#### DrClaude

Mentor
The most studied system of this kind is positronium, an "atom" made up of an electron and a positron:

Researchers have also recently created anti-hydrogen, made up of an anti-proton and a positron:

For more example, you can look up the wWikipedia article on exotic atoms:

Since our world is made up of matter instead of anti-matter, no atom with an anti-matter component is long-lived.

Staff Emeritus
Look carefully at the positronium lifetimes.

#### phyzguy

As far as we know, atoms formed exclusively from antimatter would be stable. As @DrClaude pointed out, there are experiments underway building anti-hydrogen atoms to study their properties. Of course, if these "anti-atoms" come in contact with ordinary atoms, they will annihilate.

#### ZapperZ

Staff Emeritus
2018 Award
I know these are not "atom-like", but don't we already have mesons with quark-antiquark pairs?

Zz.

Staff Emeritus
I know these are not "atom-like", but don't we already have mesons with quark-antiquark pairs?
Sure. But not stable ones.

#### atracious

So, discovered possibilities are too unstable. Are they inherently unstable, or just unstable because they differ from the norm of earth matter? Would they be stable if all the world was the same?

Would a positron be able to replace an electron at all? Would it be at all stable if it could? How would this change things in an atom?

What would happen if you had a sub atomic particle that was 3 up quarks, or 3 down quarks? Or is this impossible?

Can up (anti) quarks ever change into down (anti) quarks? Or are they forever either up or down?

#### Dr.AbeNikIanEdL

Are they inherently unstable, or just unstable because they differ from the norm of earth matter? Would they be stable if all the world was the same?
Some are just unstable in the same way some matter particles are unstable, essentially the antiparticles of stable particles are also stable in principle. Of course as was mentioned, in an environment that is dominated by matter, antiparticles will quickly annihilate. But for a free say antihydrogen atom (so a positron bound to an antiproton) in vacuum would behave basically the same as a hydrogen atom (at least we dont know any differences).

Would a positron be able to replace an electron at all? Would it be at all stable if it could? How would this change things in an atom?
A positron in vacuum is stable, only if it comes into contact with an electron they annihilate, there is nothing special about which of the is called matter and antimatter in that specific case I think, this is only important in the sense that the world around us contains way more electrons than positrons. Of course a positron and a proton would just electromagnetically repel each other, so there would be no bound state. The equivalent of an atom would be an antiproton and a positron, see above.

What would happen if you had a sub atomic particle that was 3 up quarks, or 3 down quarks? Or is this impossible?
Yes, for example in $\Delta^{++}$ https://en.m.wikipedia.org/wiki/Delta_baryon. This was basically one of the first hints for color as a quantum number.

Can up (anti) quarks ever change into down (anti) quarks? Or are they forever either up or down?
Yes again, this is for example what happens in beta decays on the level of quarks.

#### BWV

could you theoretically conduct positrons through a superconductor made of ordinary matter?

Staff Emeritus
could you theoretically conduct positrons through a superconductor made of ordinary matter?
Not very far!

#### BWV

I did find this - Positronium Hydroxide, which is a H atom bound to a positronium atom

Wouldnt it also be possible for positrons to inhabit orbital shells of an ordinary proton nucleus?

Staff Emeritus
Wouldnt it also be possible for positrons to inhabit orbital shells of an ordinary proton nucleus?
No. Like charges repel.

#### BWV

No. Like charges repel.
So the QM effects that keeps an ordinary electron separated from the nucleus would not keep a positron from being repulsed out of an orbital shell?

Staff Emeritus
So the QM effects that keeps an ordinary electron separated from the nucleus would not keep a positron from being repulsed out of an orbital shell?
What "orbital shell"? A positron cannot orbit a nucleus because the force between the positron and the nucleus is not attractive.

#### mfb

Mentor
All combinations that have matter and antimatter particles are unstable.

You need some interaction to bind particles together - the strong or the electromagnetic interaction. The strong interaction has a short range. Mesons decay, baryons plus antibaryons close together annihilate. Doesn't work.

What about the electromagnetic interaction? Electrons and positrons together annihilate so we can use at most one of them. Electrons plus antibaryons? Would need positively charged antibaryons to get an attractive force - but all these are unstable. Positrons plus baryons? Would need negatively charged baryons to get an attractive force - but all these are unstable.
Baryons and antibaryons orbiting each other based on the electromagnetic interaction? Will be short-living and end in annihilation.

Adding other leptons? A positron could be in a stable orbital around a proton+2muon combination which itself would be stable similar to a hydrogen anion. But then the muons decay...

Staff Emeritus
A positron could be in a stable orbital around a proton+2muon combination which itself would be stable similar to a hydrogen anion. But then the muons decay...
You're correct that this doesn't last any longer than the muons do, but I don't think this configuration is even stable. It is energetically favorable for it to rearrange to a muonic hydrogen atom and a (anti-)muonium atom. The H- ion is barely bound and both the muonic hydrogen atom and muonium atoms are deeply bound.

#### mfb

Mentor
The binding energy of another electron is 0.75 eV, for the muon it should be 200 times that, or 150 eV, unless I miss some nonlinearity. The binding energy of muonium is just ~14 eV, similar to regular hydrogen. In addition you would miss most of the ~13.6 eV the positron has in the initial state.

Staff Emeritus
We're getting off the track, but...

There is definitely a non-linearity (you can see it in the Hamiltonian), but you can see how the H- is bound semil-classically: one electron is near the proton forming an Hydrogen-atom like state, and the other is far away. The wavefunction is such that the expectation value of the distance between the far electron and the proton is slightly less than the expectation value of the distance between the far electron and the near electron, so you have a net attraction. (Pauli blocking is also important here, but I'll ignore it.) If I replace the electrons with negative muons, the first muon gets bound 200x deeper, but also has a wavefunction 200x closer (on average) so the second muon is bound ~200x deeper because of the mass, but only ~1/200 as deeply because muonic hydrogen is smaller. So I would expect binding of the outer muon to be of order eV (if it's bound at all).

But this is a detail. Even if you just scale everything up by 200, you can see the energetic instability. If you have (p mu- mu-) e+, the 1st muon is bound by 2.8 keV, the second by ~150 eV and the positron by 13.6 eV. If you rearrange to (p mu-) (mu- e+), the (p mu-) is bound by 2.8 keV, the (mu- e+) by half that, 1.4 keV, and if the two neutral "atoms" are bound at all, it will be of order eV. So the rearrangement is energetically favored by more than a kilovolt. Again, it's clearest semi-classically: the outer muon feels a much stronger attraction to the positron than it does to the neutral muonic hydrogen, so that's where it goes.

#### TeethWhitener

Gold Member
A positron could be in a stable orbital around a proton+2muon combination which itself would be stable similar to a hydrogen anion.
Electron-antimuon is simpler and has (I'm assuming) roughly the same lifetime.
But then the muons decay...
There's been a decent amount of work done on antimuon-electron "hydrogen atom" analogs. Yes, it's limited by the lifetime of the antimuon, but the lifetime is long enough to do chemistry, and the spin polarization of the muon is useful for probing magnetic properties of solids (using muon spin resonance, where these "chemical" effects have a real impact on the behavior of the muon).

#### mfb

Mentor
Electron-antimuon is simpler and has (I'm assuming) roughly the same lifetime.
Right, didn't think of that, I was constructing things with the proton and then didn't simplify.

Muon+proton is also used to measure the proton radius, with an interesting difference to electron-based measurements.

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#### atracious

We're getting off the track, but...

There is definitely a non-linearity (you can see it in the Hamiltonian), but you can see how the H- is bound semil-classically: one electron is near the proton forming an Hydrogen-atom like state, and the other is far away. The wavefunction is such that the expectation value of the distance between the far electron and the proton is slightly less than the expectation value of the distance between the far electron and the near electron, so you have a net attraction. (Pauli blocking is also important here, but I'll ignore it.) If I replace the electrons with negative muons, the first muon gets bound 200x deeper, but also has a wavefunction 200x closer (on average) so the second muon is bound ~200x deeper because of the mass, but only ~1/200 as deeply because muonic hydrogen is smaller. So I would expect binding of the outer muon to be of order eV (if it's bound at all).

But this is a detail. Even if you just scale everything up by 200, you can see the energetic instability. If you have (p mu- mu-) e+, the 1st muon is bound by 2.8 keV, the second by ~150 eV and the positron by 13.6 eV. If you rearrange to (p mu-) (mu- e+), the (p mu-) is bound by 2.8 keV, the (mu- e+) by half that, 1.4 keV, and if the two neutral "atoms" are bound at all, it will be of order eV. So the rearrangement is energetically favored by more than a kilovolt. Again, it's clearest semi-classically: the outer muon feels a much stronger attraction to the positron than it does to the neutral muonic hydrogen, so that's where it goes.
It's not necessarily off track. I was trying to find some sort of alternative atomic construction that is purely theoretical but could, theoretically, have been how the world was constructed, if the universe had different base particles so to speak. Something that would not have any testing yet to see if the properties would be the same. I just thought I'd try for a matter/antimatter hybrid first.

#### mfb

Mentor
I was trying to find some sort of alternative atomic construction that is purely theoretical but could, theoretically, have been how the world was constructed, if the universe had different base particles so to speak.
You might be interested in the universe without weak interaction. It removes most of the particles and one of the fundamental interactions but the resulting universe looks somewhat similar to what we have today. It even has a natural dark matter contribution, unlike the known particles in our universe.

"Matter/antimatter hybrid atomic structures?"

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