A particle's lifetime (or equivalently, its width) is a fundamental property crucial for physicists exploring the boundaries of known physics. Measuring it enables scientists to test and refine their theories, deepening their understanding of particles and their interactions.

The lifetime (τ) of a particle refers to the average amount of time it exists before decaying. Particles with shorter lifetimes decay more quickly into lighter particles, and are often referred to as unstable. The Z boson and the muon are unstable elementary particles that decay rapidly after being produced. In contrast, the electron is considered stable, possessing an effectively infinite lifetime, as its decay has never been observed experimentally. The particle width (Γ) represents the range of energies a particle can possess and is directly related to its lifetime.

Learn more in the cheat sheet: Particle decay, lifetime and width