# cross-section

In nuclear and high-energy physics, a cross-section is a measure of the likelihood of a given process occurring in an accelerator,
i.e., of particles colliding or otherwise interacting. Cross-section is
expressed as an effective target area, which can be related to the quantum-mechanical
probability of interacting by multiplying by factors such as the flux of
particles entering the interaction region. The basic unit of cross-section
for particle physics is the barn (b), equal
to 10^{-24} square centimeter (cm^{2}). Typical hadron collisions are measured in millibarns. Typical neutrino collision cross-sections are about 10^{-11} cm^{2}.