2-photon to matter

[Ankit Gupta]

I have read that an electron and positron create two gamma photons after collision but is reverse also possible ?

[swansont]

Particle/antiparticle creation can occur with a single photon of sufficient energy, if it's near a nucleus (required to conserve momentum).

[Enthalpy]

Processes are reversible, so two photons of >511keV each should make an electron-positron pair, but I have never heard about it - only pairs created by one photon >1122keV.

 

I suppose that the creation by a pair of photons is excessively rare, because it demands to concentrate their energy too much to happen often.

 

Also, pair creation from a single photon happens at the big electric field of a heavy atomic nucleus; two photons would have to coincide at the nucleus, making it less probable.

[Sensei]

Processes are reversible, so two photons of >511keV each should make an electron-positron pair, but I have never heard about it

 

http://en.wikipedia.org/wiki/Two-photon_physics

 

"Two-photon physics, also called gamma–gamma physics, is a branch of particle physics that describes the interactions between two photons. If the energy at the center of mass system of the two photons is large enough, matter can be created."

 

Rare? Of course. Otherwise we wouldn't be here.

If gamma photons would be present in large quantity, whole matter would be constantly ionized at least.

In the worst scenario high energy gamma photon can split nucleus to parts.

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

[mathematic]

Immediately after the big bang photon-photon collisions were very common, leading to the creation of matter as we know it.

[Ankit Gupta]

Immediately after the big bang photon-photon collisions were very common, leading to the creation of matter as we know it.

do two photons interact with each other ?

[swansont]

do two photons interact with each other ?

 

Only rarely.

[Ankit Gupta]

Only rarely.

when ?

[swansont]

http://en.wikipedia.org/wiki/Two-photon_physics

[Ankit Gupta]

But they don't have charge neither mass then how can they intrect

[ajb]

But they don't have charge neither mass then how can they intrect

The mass is not important here, but the fact they have no electric charge is. There is no direct interaction (no tree diagrams) here. The photons interact via virtual electrons and anti-electrons meaning that we have loops in the Feynman diagrams as we require charge conservation.

 

All together this means that the interactions are suppressed, which leads to swansont's comment that they only interact rarely.

[JonG]

do two photons interact with each other ?

 

In addition to what has already been mentioned, there are multiphoton processes, which might not be seen as the "photons interacting with each other", but which involve several photons interacting with an atom simultaneously. A 2-photon process, for example, would involve two photons, each carrying energy E, being absorbed by an atom and giving rise to a transition requiring energy 2E.

 

Processes of this sort are are only observed with light of very high intensity as might be generated by pulsed lasers. Classically, they are described as a kind of non-linear effect. The non-linearity in the interaction between photons and an atom is what causes two or more photons to be absorbed at once. For normal light intensities, 2-photon transition would actually contravene selection rules, but they can become the dominant process at high light intensities.

[Enthalpy]

Imagine, instead of one photon exceeding 1022keV, two photons slightly over 511keV each, that are to make an electron-positron pair.

 

Wiki describes it as "first photon fluctuates into a virtual pair, second photon interacts with the pair".

 

The virtual pair would have -250keV per electron.

- This gives a life expectancy of 10^-21s, during which light propagates by 0.4pm, so the second photon has little time to be there.

- The electrons can "move" from their virtual appearance point, or rather delocalize as an evanescent wave does, by 0.4pm. Over such a distance, the second photon must bring the missing 250keV per electron, so the second photon must concentrate itself a lot, making the event improbable.

 

(Both 0.4pm coincide by chance, just because the virtual electrons miss half their mass of energy)

 

Imagine a second 500keV photon in a collider, spread over (1mm)²: it must concentrate to (0.4pm)² to provide the missing energy, which is about 10^-19 probable.