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touqra
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How did they experimentally verify that there is pair creation and annihilation in the vacuum? What kind of particles usually pops in and out of the vacuum?
smallphi said:A strong electric field has to create actual observable pairs of charged particles out of otherwise empty space but that is not experimentally verified yet. The lasers we have are still not powerful enough.
ahrkron said:The wikipedia article is a nice starting point for this:
http://en.wikipedia.org/wiki/Casimir_effect
There is also a beautiful picture related to it in
http://antwrp.gsfc.nasa.gov/apod/ap061217.html
touqra said:How did they experimentally verify that there is pair creation and annihilation in the vacuum? What kind of particles usually pops in and out of the vacuum?
They don't. At least not yet.touqra said:How did they experimentally verify that there is pair creation and annihilation in the vacuum?
Just to clarify... Pair creation by an intense EM field has indeed beensmallphi said:A strong electric field has to create actual observable pairs of charged particles out of otherwise empty space but that is not experimentally verified yet. The lasers we have are still not powerful enough.
I don't think that this can be taken as an experimental proof of the Schwinger effect, in which a static electric field should produce pairs.strangerep said:Just to clarify... Pair creation by an intense EM field has indeed been
understood and experimentally observed for decades in relativistic heavy-ion
collisions. The setup is that 2 heavy nuclei collide, temporarily creating a state
whose Coulomb field is so immense that it can produce (on-shell) pairs. I.e: the
energy density of the field is greater than the combined masses of the
electron & positron. This is explained in more detailed in some of Greiner's
textbooks, e.g: "QED of Strong Fields".
I'm surprised to hear such a view, since the results of these experimentsDemystifier said:I don't think [pair-production from intense
Coulomb field of large-Z nuclei in heavy-ion collisions] can be taken as an experimental proof of the Schwinger effect, in which a static electric field should produce pairs.
strangerep said:In the Schwinger effect, an implied consequence is that a sufficiently
strong field could not persist very long - because pair production would
carry away energy-momentum. So creating a nucleus with Z >= 139
and observing the results seems like a reasonable way to investigate
the phenomenon.
MaWM said:When a gamma ray photon creates a positron-electron pair, isn't this equivalent to a virtual e+ - e- pair being torn apart and made real by the energy in the photon's electromagnetic field?
Barmecides said:The initial question was "How did they experimentally verify that there is pair creation and annihilation in the vacuum?"
ZapperZ said:But that question, technically, has been answered in MaWM response.
If you shoot a gamma photon into a crystal, and the gamma photon disappears, an electron-positron pair comes out, and the crystal remains the same, have we then shown an experimental verification of the question? I would say it has, and the physics that describes this process would also confirm that.
I'm not an expert on the details, so I'll mention the few things I'm aware of...meopemuk said:I am not familiar with this experiment and its analysis. However, it seems logical to me that when we collide two heavy nuclei with suffient energy, there could be a number of different channels for producing electron-positron pairs. (For example, such pairs can be produced simply in collisions of two electrons if the center-of-mass energy is high enough.) Was it possible to separate all these channels and say exactly which portion of electron-positron pairs was produced by the strong field, as opposed to any other reason?
strangerep said:Sorry I can't be more definitive.
Yes, I was just about to say the same thing. So let me try to answer theBarmecides said:I'm not sure that the initial question was talking about photon conversion into an e+e- pair when interacting with an electromagnetic field.
He wanted to know if we already have been observing directly pair creation from vacuum which is quite different !
My point is, if we deal with collisions, then the field is far from being static. On the other hand, the Schwinger effect talks specifically about static fields. I am not surprised that a collision may lead to a pair creation, but I am very skeptical about the claim that a STATIC field may produce a pair. See, e.g.,strangerep said:I'm surprised to hear such a view, since the results of these experiments
are quite extensive and detailed. They've been in the mainstream for quite
a while.
In the Schwinger effect, an implied consequence is that a sufficiently
strong field could not persist very long - because pair production would
carry away energy-momentum. So creating a nucleus with Z >= 139
and observing the results seems like a reasonable way to investigate
the phenomenon.
"the energy exceeding the rest mass of the two particles which in turn means exceeding the rest energy of the two particles". Are you implying translation from virtual particles to real particles violates conservation of energy? I find this hard to believe. Please make yourself clearer.smallphi said:Quote from V. F. Mukhanov and S. Winitzki "Introduction to Quantum Fields
in Classical Backgrounds", available for free (still) at
http://www.theorie.physik.uni-muenchen.de/~serge/T6/book.pdf
A static electric field in empty space can create electron-positron (e+e−) pairs. This
effect, called the Schwinger effect, is currently on the verge of being experimentally
verified.
To understand the Schwinger effect qualitatively, we may imagine a virtual e+e−
pair in a constant electric field of strength E. If the particles move apart from each
other to a distance l, they will receive the energy leE from the electric field. If this
energy exceeds the rest mass of the two particles, leE ≥ 2m_e, the pair will become
real and the particles will continue to move apart. The typical separation of the virtual
pair is of order of the Compton wavelength 2π/m_e. More precisely, the probability of
separation by a distance l turns out to be P ~ exp (−π m_e l). Therefore the probability
of creating an e+e− pair is
P ~ exp(−m_e^2 /eE)
The exact formula for the probability P can be obtained from a full (but rather lengthy)
consideration using quantum electrodynamics.
Pair creation and annihilation is a phenomenon in quantum physics where a particle and its antiparticle are created or destroyed simultaneously.
Pair creation and annihilation can occur when a high-energy photon interacts with a nucleus or an electric field, resulting in the creation of a particle and an antiparticle or the annihilation of a particle-antiparticle pair.
Pair creation and annihilation are important in particle physics as they help explain the behavior of subatomic particles and their interactions with each other. They also play a crucial role in the study of quantum field theory and the Standard Model.
Yes, pair creation and annihilation have been observed experimentally in particle accelerators such as the Large Hadron Collider (LHC) and in cosmic ray experiments. These observations provide evidence for the existence of antiparticles and confirm the principles of quantum physics.
Pair creation and annihilation are inverse processes of each other. In pair creation, a particle and its antiparticle are created from energy, while in annihilation, a particle and its antiparticle are destroyed, resulting in the release of energy.