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The muon is an elementary particle with negative electric charge (-1) and a spin of ½. This is similar to an electron. A muon is combined with an electron, a tau, and three neutrinos, to form a lepton. A muon does not have any sub-structure.

The muon has a lifetime of 2.2μs. This is a long decay lifetime which is due to the weak interaction. A muon decay will produce at least three particles. These particles must include one electron of the same charge as the original muon and two neutrinos of different charges.

Similarly to other elementary particles, the muon has a corresponding antiparticle of opposite charge (+1) but equal and in spin. The antimuon is also referred to as a positive muon. Muon’s are denoted by μ- and μ+. They were previously called mu mesons however they are not classified as mesons by modern particle physicists.

Muons have a mass which is about 200 times the mass of an electron. The mass is 105.7MeV/c2. Due to the muon’s interactions being very similar to those of an electron, a muon can be thought to be a heavier version of the electron. However, muons are not as sharlply accelerated when they encounter electromagnetic fields and do not emit as much bremsstrahlung. This property allows muons of a given energy to penetrate far more deeply into matter than electrons since the deceleration of electrons and muons is primarily due to energy loss by the bremsstrahlung mechanism.

Fine structure constant

Please help with the following particle physics problem. What is meant by the 'fine structure constant'? Explain what the fine structure constant tells us about the relative probability of the formation of a three particle event (muon antimuon and photon) compared with the formation of a muon and antimuon pair.