The relativistic Breit–Wigner distribution (after the 1936 nuclear resonance formula of Gregory Breit and Eugene Wigner) is a continuous probability distribution with the following probability density function, where k is a constant of proportionality, equal to with (This equation is written using natural units, ħ = c = 1.) In the limit of vanishing width, Γ→0, the particle becomes stable as the Lorentzian distribution f sharpens infinitely to 2M δ(E2−M2). .(Further information: Cauchy distribution)