Barn (unit)

Unit for cross sectional area used in high-energy physics

A barn (symbol: b) is a non-SI metric unit of area equal to 10−28 m² (100 fm2). This corresponds to the area of a square with side 10−14 m (10 fm) or a circle of diameter approximately 1.128×10−14 m (11.28 fm). Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is also used in all fields of high-energy physics to express the cross sections of any scattering process, and is best understood as a measure of the probability of interaction between small particles.

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