In the mid-1930s, physicists thought they knew all the subatomic particles of nature - the proton, neutron, and electron of the atom. However, in 1936 the muon was discovered - a new particle having such surprising properties that Nobel laureate I.I. Rabi quipped "Who ordered that?" when informed of the discovery. Evidence that a new light boson may exist has recently been published. If the discovery is confirmed, such a boson is not part of the Standard Model of Particle Physics - potentially leading to another "Who ordered that?" moment for physicists.
Read the full article: Who ordered that? An unexpected new particle shakes the Standard Model