The Higgs boson is an elementary particle in the Standard Model of particle physics. It is the quantum excitation of the Higgs field—a fundamental field of crucial importance to particle physics theory, first suspected to exist in the 1960s, that unlike other known fields such as the electromagnetic field, takes a non-zero constant value almost everywhere. The question of the Higgs field's existence has been the last unverified part of the Standard Model of particle physics and, according to some, "the central problem in particle physics".