At particles´ interaction may take place the reactions of interconversion. That process is regulated by the conservation laws. The conservation laws that all particle interactions must obey are known mechanical energy, momentum and angular momentum conservations and additional typical for particle physics conservations. Last characterize the properties of particles before and after interaction. Let´s remember that all particles are subdivided into groups in accordance with their properties. In particular, by values of it´s rest masses it distinguishes leptons (light particles), mesons (middle) and baryons (hard particles), by sign of electric charge it distinguishes positive, negative (with absolute value |e|) and electrically neutral particles. Also particles are sorted by a spin number, by a value of strangeness etc. To mark particles incoming to group of leptons they are attached characteristic called lepton number L. It takes that all leptons have a lepton number L = +1, all antilepton have a lepton number L = -1, for all other particles L = 0. Leptons come in three families. In the electron family is the electron, electron neutrino, and their antiparticles. In the muon family is the muon, muon neutrino, and their antiparticles. Finally, in the tau family is the tau, tau neutrino, and their antiparticles. To characterize particles from baryon group conception of baryon number introduced. All baryons (for example, protons, neutrons, and the delta resonance particles) are assigned a baryon number B = +1, all antibaryons (for example, antiprotons, antineutrons, and the antidelta resonance particles) are assigned a baryon number B = -1, and all other particles (for example, electrons, neutrinos, pions, and photons) are assigned a baryon number of 0. So three most important in particle physics laws are electric charge, baryon number, and lepton number conservations. Two first from them state that the sum of the electric charges and the sum of the baryon numbers of the constituents before an interaction takes place must be equal to the sum of the electric charges and the sum of the baryon numbers of the constituents after the interaction is complete. The law of lepton number conservation states that in each family independently the lepton number before an interaction takes place (the sum of the lepton numbers of all constituents) must be equal to the lepton number after the interaction is complete. Thus, electron-lepton number must be conserved, muon-lepton number must be conserved, and tau-lepton number must be conserved independently. In this simulation you slam particles together and observe interaction. Use switches to choose two incoming particles and run the simulation. After interaction you will see one known outgoing particle and other unknown. You must apply all needed conservation laws to determine unknown particle. Choose from proposed list calculated particle and check your answer.