The Large Hadron Collider forward (LHCf) experiment uses particles thrown forward by collisions in the Large Hadron Collider as a source to simulate cosmic rays in laboratory conditions. Cosmic rays are naturally occurring charged particles from outer space that constantly bombard the Earth's atmosphere. They collide with nuclei in the upper atmosphere, triggering a cascade of particles that reaches ground level. Studying how collisions inside the LHC cause similar cascades of particles will help physicists to interpret and calibrate large-scale cosmic-ray experiments that can cover thousands of kilometres.

LHCf is made up of two detectors which sit along the LHC beamline, at 140 metres either side of the ATLAS collision point. The location allows the observation of particles at nearly zero degrees to the proton beam direction. Each of the two detectors weighs only 40 kilograms and measures 30 cm long by 80 cm high and 10 cm wide. The LHCf experiment involves 30 scientists from 9 institutes in 5 countries (November 2012).