Some basic concepts (and numbers) A  meson decaying at rest produces pairs of neutral or charged kaons with branching ratios of ~34% and ~49%,respectively Daughter particles are monochromatic, P ch ~ 125 MeV/c, P neu ~ 110 MeV/c In resonant e + e  collisions, particles fluxes are: 1.5 x 10 6 K ± pairs/pb  1 1.
{}