At Brookhaven Laboratory, a particle accelerator is used to test the nature of neutrinos. The proton beam is fired at a beryllium target, producing pions (combined up and down quarks), which rapidly decay into muons and neutrinos. They then encounter a 13-meter steel barrier (made from the hull of a decommissioned battleship). The muons crash, and the neutrinos pass unscathed. Of the 100 trillion neutrinos passed, 51 are detected and generate a muon, never an electron. Muon neutrinos (of a muon flavor) are therefore different from electron neutrinos (of an electron flavor).
