dEdx

dEdx, commonly written as dE/dx, denotes the differential energy loss of a charged particle per unit path length as it traverses matter. This quantity represents the energy deposited by the particle in ionization and excitation of atoms along its trajectory. In detector physics it is often quoted as either dE/dx (MeV per centimeter) or as the reduced form dE/dx in units of MeV cm^2/g, the latter being normalized to material density.

The mean energy loss is described by the Bethe-Bloch formula, which depends on the particle’s charge, velocity (often expressed as β = v/c and γ = 1/√(1−β^2)), and the properties of the material (atomic number Z, atomic mass A, mean excitation potential I, and density). In general, dE/dx decreases with increasing velocity at lower speeds, reaches a minimum for highly relativistic particles (the minimum ionizing region, typically βγ around a few), and then slowly rises due to density effects at very high velocities. Near the end of a particle’s range, energy loss increases sharply as the particle slows down, producing a Bragg peak. Energy loss fluctuations are governed by Landau distributions, so experimental determinations often use truncated means or detailed calorimetric methods.

Applications of dEdx measurements include particle identification in tracking detectors, such as time projection chambers and silicon trackers, where the observed dE/dx versus momentum helps distinguish particle species. Accurate dEdx calibration and modeling are essential for detector performance and for interpreting energy deposition in various materials.