Muon and neutrino collimation in extensive air shower cores

Detailed simulations of extensive air showers have been carried out with the CORSIKA program in order to evaluate the energy brought by the different shower components at ground level and transmitted underground. A special attention is given to the angular distributions and to the collimation of beams penetrating deep underground or underwater. The natural collimation of high energy particles in extensive air shower cores results mainly from the ratio between the transverse and the longitudinal momenta of secondary particles generated in the earliest interactions. This collimation is partly conserved by the high energy muons and neutrinos. It is comparable to the magnetic focusing of charged pions and kaons decaying in tunnels of suitable length after production in accelerators. Such is the case for neutrino beams of KEK J-PARC/T2K (300 km to Kamiokande), OPERA (730 km to Gran Sasso) and MINOS (735 km to Irvine Mine).