Theory of Particle Identification

dE/dx is an unsuitable quantity to deal with PID, what is needed are straggling functions. The theory and understanding needed for PID will be presented. Instrumental effects must also be calculated and understood. 1 Introduction. 1.1 General concepts The concept dE/dx representing the mean rate of energy loss in an absorber [1] is used inappropriately in the description of the physics of most high energy particle detectors. Consider Fig. 1 which gives the probability density function (p.d.f.) f(∆) for energy losses ∆ of particles 1 with βγ = 3.