What Happens When Matter Meets Antimatter in Our Universe?

[spideyinspace]

i have a doubt..what would happen when matter and antimatter meets..e.g what would be the result of neutrino + anti neutrino...would they go off from our universe

 

[cristo]

No, they would not "go off from our universe." When a particle and an antiparticle meet, they annihilate, and produce two photons.

 

[spideyinspace]

No, they would not "go off from our universe." When a particle and an antiparticle meet, they annihilate, and produce two photons.

is this is the case with all matter and antimatter..does all matter+antimatter gives two photons?then what is the probabalility that photon becoming which matter and which antimatter?

 

[mathman]

then what is the probabalility that photon becoming which matter and which antimatter?

Please clarify this sentence! Photons are neither matter nor antimatter - if that's what you are asking.

 

[spideyinspace]

Please clarify this sentence! Photons are neither matter nor antimatter - if that's what you are asking.

what i mean is,electron and positron gives photons,neutrino and anti neutrino also gives photons,so if there is chance for photons to become again matter and antimatter, what is the probability that it would become electron and positron,neutrino and anti neutrino?...

 

[mathman]

what i mean is,electron and positron gives photons,neutrino and anti neutrino also gives photons,so if there is chance for photons to become again matter and antimatter, what is the probability that it would become electron and positron,neutrino and anti neutrino?...

It depends on a lot of conditions: The energy of the photon for starters, the environment.

I am most familiar with the electron-positron case. Here the minimum photon energy is 1.022 Mev (the rest mass of the the positron + electron) - gamma rays. Because of momentum consideration, it won't happen by itself, but only with interaction involving a nucleus (for example) - with probability a function of at. wt. of nuclide as well as the energy of the photon. Also for very high concentrations of photons (like just after the big bang), two photons could collide to produce an electron-positron pair.

For other pairs, such as neutrino-antineutrino or proton-antiproton, the same principles apply, with different energy requirements and different probabilities.

 

[blechman]

what i mean is,electron and positron gives photons,neutrino and anti neutrino also gives photons,so if there is chance for photons to become again matter and antimatter, what is the probability that it would become electron and positron,neutrino and anti neutrino?...

Neutrinos are electrically neutral, and photons only couple to charge, so how exactly does neutrino-antineutrino annihilate to photons?!

The only thing a neutrino-antineutrino pair can annihliate to are Z-bosons, which are too heavy to be produced explicitly, so they must be virtual, and when these (highly virtual) Z bosons decay, they can go to lots of things (quark-antiquark/lepton-antilepton/etc).

So I think the correct answer is that when a particle and its antiparticle meet, they annihilate into energy, which could come in many forms.

 

[spideyinspace]

Neutrinos are electrically neutral, and photons only couple to charge, so how exactly does neutrino-antineutrino annihilate to photons?!

The only thing a neutrino-antineutrino pair can annihliate to are Z-bosons, which are too heavy to be produced explicitly, so they must be virtual, and when these (highly virtual) Z bosons decay, they can go to lots of things (quark-antiquark/lepton-antilepton/etc).

So I think the correct answer is that when a particle and its antiparticle meet, they annihilate into energy, which could come in many forms.

so you say neutrinos and anti neutrinos will not give photons...is there any any proof or website related to this..

 

[Parlyne]

Neutrinos are electrically neutral, and photons only couple to charge, so how exactly does neutrino-antineutrino annihilate to photons?!

Through loops, or course. For example, the pair could produce a virtual e/W loop which could radiate the photons.

The only thing a neutrino-antineutrino pair can annihliate to are Z-bosons, which are too heavy to be produced explicitly, so they must be virtual, and when these (highly virtual) Z bosons decay, they can go to lots of things (quark-antiquark/lepton-antilepton/etc).

The $\nu / \overline{\nu}$ pair could also directly annihilate to a $W^+/W^-$ pair through a virtual electron. Either this or annihilation to a Z (or multiple Zs) would require extraordinarily energetic neutrinos. And, even this, the Ws or Z would quickly decay. So, the observed processes will be those that use these processes to annihilate the neutrinos and, then, have the heavy bosons either decay or only exist as virtual particles in the first place.

 

[Parlyne]

so you say neutrinos and anti neutrinos will not give photons...is there any any proof or website related to this..

In fact, they can annihilate to photons. For lower energy neutrinos, this is, in fact, the only thing the could annihilate to. However, any interaction that could do this is highly suppressed, first by the fact that neutrinos only directly interact through the weak force, which is very weak, and second by the fact that this process can only occur at second order in the perturbation expansion.

 

[blechman]

OK, neutrinos can annihliate into photons through EW-loops, this is true. But it's subdominant, and not very likely. In fact, probably the most likely thing that would happen if a neutrino met its antineutrino in a bar is that they would completely ignore each other! The elastic scattering should be much larger than the annihilation channel, since it can happen at tree level through only one (virtual) Z-boson exchange, rather than requiring two or more virtual EQ gauge bosons (and possibly also a loop).

 

[quantumfireball]

the electron positron have an amplitude of just scattreing of each other by
exchanging momenta,
its not compulsory that they have to anhillate

 

[Parlyne]

OK, neutrinos can annihliate into photons through EW-loops, this is true. But it's subdominant, and not very likely. In fact, probably the most likely thing that would happen if a neutrino met its antineutrino in a bar is that they would completely ignore each other! The elastic scattering should be much larger than the annihilation channel, since it can happen at tree level through only one (virtual) Z-boson exchange, rather than requiring two or more virtual EQ gauge bosons (and possibly also a loop).

Certainly true. But, if we're talking specifically about annihilation processes, you need to get to somewhat significant energies before any decay channel other than photons opens up in the first place. So, to that extent, it's still the dominant annihilation process. It's simply far less likely than elastic scattering.

 

[blechman]

Certainly true. But, if we're talking specifically about annihilation processes, you need to get to somewhat significant energies before any decay channel other than photons opens up in the first place. So, to that extent, it's still the dominant annihilation process. It's simply far less likely than elastic scattering.

I'll agree with that.

 

[spideyinspace]

Thank you for all replies..
shall we conclude that
lower energy neutrinos and antineutrinos can annihilate to photons..
higher energy neutrinos and antineutrinos annihilate to quark-antiquark or lepton-antilepton..if this is wrong can one give a conclusion for this topic(neutrino+antineutrino)...

 

[malawi_glenn]

A general rule, the higher energy you have in the CM of two colliding anti particles, the more options for the final decay state. The more energy available: the more particles you can reach.