Electromagnetic shower

A cascade driven primarily by electron and Positron bremsstrahlung and photon pair production in matter. An electromagnetic calorimeter estimates the incident energy from the deposited cascade. Escaping shower particles and incomplete instrument coverage require containment and response corrections.

If every particle branches into two equal-energy daughters after one radiation length, the multiplicity is $2^n$ and each energy is $E_0/2^n$. Multiplication stops at the critical energy of an electromagnetic shower. This predicts a branching depth, not a realistic containment quantile: stochastic interaction distances, unequal radiation spectra and the residual stopping range produce a longitudinal tail.

The approximate electron energy at which radiative and collisional energy-loss rates are equal in a given material. Below it, ionization increasingly dominates and multiplication of the electromagnetic shower ends. It is material dependent, not a universal particle constant.