/*! @page  physicsref The Physics List

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The physics list is the class responsible for the different particles and the interactions to consider during the simulation. If it is possible to declare all the particles and all the physics processes in the physics list, another method consists in building registers for the different types of particles. Those register are then collected in the physics list file LEMuSRPhysicsList.cc, building a so-called modular physics list class. The gain of clarity and precision is the main advantadge of this procedure.

\gf provides comprehensive libraries about particles and their interactions. They can be accessed in the subdirectories Geant4.version/source/particles and Geant4.version/source/processes. 

Most of the registers used in the \lemu experiment were taken from \gf examples, and only the muon physics was specified:
 * - LEMuSREMPhysics: electromagnetic processes. Definition of the electron, positron and their neutrinos, and of the photon #gamma. The processes implemented are the photoelectric effect, the compton effect and the pair production for the gamma, the multiple scattering and bremstrahlung and the ionisation for the electron and positron. The neutrinos are not considered to interact.
 * - LEMuSRIonPhysics: considers the common hydrogen-based ions and their scattering processes. This register is not needed for the simulation.
 * - LEMuSRHadronPhysics: constructs the mesons and the baryons and their common interactions.
 * - LEMuSRGeneralPhysics: is used to apply general processes to the particles, like enabling decay processes or applying user limitations and cuts on energy, step length or track size.
 * - LEMuSRMuonPhysics: muon physics. Are constructed the muon plus, the muon minus, the muonium and the neutrinos.
* .
The transportation process is by default attached to the registered particles.


\section phys_muprocesses Processes for muonic particles

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