The inverse femtobarn (fb⁻¹) is a measurement of particle-collision events per femtobarn; a measure of both the collision number and the amount of data collected. 

One inverse femtobarn corresponds to approximately 100 trillion (10¹²) proton-proton collisions. Over a period of time, two streams of particles with a cross-sectional area, measured in femtobarns, are directed to collide. The total number of collisions is directly proportional to the luminosity of the collisions measured over this time.

Calculate the collision count by multiplying the integrated luminosity by the sum of the cross-section for those collision processes. This count is then expressed as inverse femtobarns for the time period (100 fb⁻¹ in nine months).

Note: Do not use inverse femtobarn in the public section of the website where it can be avoided – it is unnecessarily technical. Convert to approximate numbers of collisions instead.