 Invariant mass

Rest mass is the invariant mass $m$ in the relativistic energy-momentum relation. It equals the energy measured in the particle's rest frame divided by $c^2$.

Invariant mass is a concept from physics, particularly in the context of special relativity and particle physics. It refers to the mass of a system of particles as measured in a specific reference frame, and it remains constant regardless of the motion of the observer. Invariant mass is particularly useful for understanding systems involving multiple particles or decaying particles. In technical terms, the invariant mass \( M \) of a system of particles can be calculated using the energy and momentum of those particles.