 Similarly, one can construct an eigenbasis out of three neutrino states of definite mass, formula_4, formula_5, and formula_6, which diagonalize the neutrino's free-particle Hamiltonian.Observations of neutrino oscillation have experimentally determined that for neutrinos, as for quarks, these two eigenbases are not the same - they are "rotated" relative to each other.Each flavor eigenstate can thus be written as a superposition of mass eigenstates, and vice versa.