Answer:

muon

Answer	Crossword Clue
MUON	Short-lived particle
MUON	Unstable particle
MUON	Unstable subatomic particle

MUON	Particle that can temporarily replace an electron
MUON	Subatomic particle
MUON	Atomic particle
MUON	Type of unstable particle
MUON	Charged lepton
MUON	Physics particle
MUON	Elementary particle
MUON	Unstable lepton

MUON	Particle created by a cosmic ray
MUON	Subatomic particle more massive than an electron
MUON	Short-lived, charged lepton
MUON	Subatomic bit
MUON	Particle of cosmic radiation
MUON	Short-lived atomic particle