2, here = 2. The distribution is the solution of the differential equation for the amplitude squared w.r.t. the energy energy (frequency), in such a classical forced oscillator, with Gaussian broadening In experiment, the incident beam that produces resonance always has some spread of energy around a central value. Usually, that is a Gaussian/normal distribution. The resulting resonance shape in this case is given by the convolution of the Breit–Wigner and the Gaussian distribution, This function can be simplified by introducing new variables, to obtain where the relativistic line broadening function has the following definition, is the relativistic counterpart of the similar line-broadening function for the Voigt profile used in spectroscopy (see also Section 7.19 of ). References Continuous distributions Particle physics