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mysearch
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Hi,
I am trying to get a better understanding of what aspects of an electronpositron collision can be physically observed as opposed to mathematically inferred. In part, my confusion is based on a number of different sources, e.g. see links below, which seem to adopt different approaches to describing the same thing, i.e.
Graphically, we appear to have an electron [e] and positron [e+] colliding and annihilating at [t1,x], which results in a photon being created, which then ‘transmutes’ back into an electron and positron at [t2,x]. As such, the photon seems to exists for [t2t1] but travels no distance.
We appears to have a positron [e+] scattering at a point [x1,t], while the electron scatters at a point [x2,t]. Based on a lefttoright timescale, it seems to suggest zero time, but a separation [x2x1].
Thanks
I am trying to get a better understanding of what aspects of an electronpositron collision can be physically observed as opposed to mathematically inferred. In part, my confusion is based on a number of different sources, e.g. see links below, which seem to adopt different approaches to describing the same thing, i.e.
 Scattering or annihilation: Collision crosssection
 Feynman diagrams: probability amplitude and rules
 Dirac notation: transition amplitudes, creation/destruction operators
 Are (p1+p2)=(p3+p4) representative of initial and final observable states, such that the conservation of momentum and charge have to be maintained?
 Does the probability of any final observable outcome depend on the energy of the initial state, e.g. does the probability of collision also have to account for the collision crosssection, if defined as a function of energy?
 Is it is true say that annihilation and scattering reflect only the main possibilities of many other potential permutations; although other permutations may have diminishing probability amplitudes associated with each additional vertex coupling, which are not observable?
Graphically, we appear to have an electron [e] and positron [e+] colliding and annihilating at [t1,x], which results in a photon being created, which then ‘transmutes’ back into an electron and positron at [t2,x]. As such, the photon seems to exists for [t2t1] but travels no distance.
 In the specific case of electronpositron annihilation, can the photon continue to exist as it doesn’t seem to violate any obvious conservation laws and would appear to have one less coupling factor? – see question regarding whether this is a virtual photon below.
 What quantum process describes a photon of energy changing back to an electronpositron pair, i.e. it doesn’t appear to result in a lower energy state?
We appears to have a positron [e+] scattering at a point [x1,t], while the electron scatters at a point [x2,t]. Based on a lefttoright timescale, it seems to suggest zero time, but a separation [x2x1].
 Is this sort of physical interpretation simply inappropriate, if so, what are these diagrams actually trying to convey by alluding to timedistance axes?
 Does the photon in either diagram have any observable existence, i.e. does it have to be described as a virtual photon and does it have to comply with all conservation laws?
 Is there any physical evidence that the virtual photon is ‘really’ created or is this simply an inference of the maths?
 In terms of the scattering process, does the physical separation [x2x1] essentially correspond to the dynamic energy cross section of the collision?
 Does scattering require more initial state energy than annihilation?
Thanks
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