= distribution of different particles in the grid cells (class [http://flc.web.lal.in2p3.fr/mdi/BBSIM/guineapig++Prod/guineapig++trunk/doc/html/class_grid.html GRID] ) =


There are three types of particles to be distributed on the grid
 * [wiki:guiNeaPig/DistCharged    charged] particles of the beams electrons, positrons...)
 * particles sected for backgroud calculations (on statistical criteria)
 * virtual photons