# What is a non-gaussian tail of momentum resolution?

While reading about the reconstruction of high transverse momentum muons in particle detectors I came across the following statement which I do not understand:

Showers and radiative loss account mainly for the non-Gaussian tails of momentum resolution.

I know that momentum resolution is defined as $\Delta$P/P where $\Delta$P is the width of the Gaussian distribution of the deviation of the observed value from the true value. So my question is, what does non-Gaussian tails of momentum resolution mean?

• A proper answer would be large. Particle/matter interaction have various physical mechanisms that add up to energy loss/deposition and also scattering. The sum total of the random process are sort of Gaussian--say out to $3\sigma$, and then (in my experience) there's a power law fall off. The non Gaussian nature is used cases by rare large energy (or angle) events that are too few to let the Central Limit Th'rm kick in. For energy loss (scattering) look into the Landau Distribution (non-Gaussian tails of multiple Coulomb scattering). – JEB Feb 14 '18 at 16:42