The probability of producing the resonance at a given energy E is proportional to f (E), so that a plot of the production rate of the unstable particle as a function of energy traces out the shape of the relativistic Breit–Wigner distribution. Note that for values of E off the maximum at M such that | E − M | = M Γ, (hence | E − M | = Γ/2 for M ≫ Γ), the distribution f has attenuated to half its maximum value, which justifies the name for Γ, width at half-maximum.