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Positrons can be easily produced in pair production reactions, when gamma rays with energy more than 1 MeV interact in the field of a nucleus, so there is no problem in producing them at accelerator sites or even from decay products of reactor cores. For LEP in particular the positrons were generated by using an electron beam hitting a target that would ...

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If the two objects are equal in mass (or close to it), both orbit their barycenter, which would be a point outside either body. If one object suddenly loses half its mass, the COM of the binary system moves with respect to the current locations of both objects, resulting in changes to acceleration for both ($a=\frac{GM}{ r^2}$, where r is distance to ). i.e, ...

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Try working back through the maths if you assume that Time itself is a negative form of matter and energy. We are very good at measuring time, but so far have never managed to explain what exactly it is. Time was created in the Big Bang to balance the creation of matter and energy. It displays a negative gravitational force.

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an interesting question, no doubts. Indeed most of the time we rely on conservation of quantum numbers but there is an underlying structure to this. In principle changing a particle with an antiparticle amounts to a CP transformation. This is a symmetry for electromagnetic and (supposedly) strong interactions. Because of this, it doesn't really matter what ...

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It started with conservation of quantum numbers, from baryon number when we did not know about quarks, to lepton number, when we discovered the positron.For the neutrino momentum and energy conservation played a role too, since it is only seen as a missing mass. In time the symmetries in the assignments of the quantum numbers became more and more evident ...

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