The decay length (𝜆) is the average distance a particle travels before it decays, determined by its velocity (v) and lifetime (𝜏₀). For particles moving at low speeds, the decay length is simply the product of the particle’s speed and lifetime, 𝜆= v*𝜏₀. However, when a particle moves at relativistic speed, close to the speed of light, time dilation increases the particle’s lifetime, and the decay length becomes 𝜆= v*𝜏₀* γ. The Lorentz factor (γ) accounts for relativistic time dilation. It is the ratio of the particle’s lifetime as measured in the observer’s frame to its lifetime as measured in the particle’s rest frame. The proper decay length is a direct measure of the particle lifetime. It is determined by the distance the particle would travel at the speed of light before it decays, not considering time dilation, becoming 𝜆= c𝜏₀.