Symbol b.

A unit of area. A barn is 10⁻²⁸ m² (100 fm²), about the cross-sectional area of a uranium nucleus.

A barn expresses the cross-section of any scattering process, which relates to the probability of interaction between small particles.

Sample size at CERN is often expressed in femtobarns and luminosity is expressed in inverse femtobarns.

Whenever the terms barn, femtobarn or inverse femtobarn appear in the public section of the website, they should be defined with an accompanying clause:

The LHC collected 5 inverse femtobarns of data last year, a measure of acclerator performance equivalent to about 500 trillion proton-proton collisions.

Use square brackets to add this information to quotes:

"Once we reach 6 inverse femtobarns [the equivalent of 300,000 CDs of data] we will be sure if the Higgs exists or not," says Smith.