In scattering theory and accelerator physics, luminosity (L) is the ratio of the number of events detected (dN) in a certain period of time (dt) to the cross-section (σ):[1] It has the dimensions of events on time on area, and is usually expressed in the cgs units of cm−2·s−1 or the non-SI units of b−1·s−1.
In practice, L is dependent on the particle beam parameters, such as beam width and particle flow rate, as well as the target properties, such as target size and density.
[1] A related quantity is integrated luminosity (Lint), which is the integral of the luminosity with respect to time:[1] The luminosity and integrated luminosity are useful values to characterize the performance of a particle accelerator.
In particular, all collider experiments aim to maximize their integrated luminosities, as the higher the integrated luminosity, the more data is available to analyze.
[1] Here are a few examples of the luminosity of certain accelerators.