LHCf

LHCf, short for Large Hadron Collider forward, is a CERN experiment at the Large Hadron Collider designed to study neutral particles produced at very small angles relative to the proton beams. Its measurements of forward photons and neutral hadrons are intended to improve the hadronic interaction models used to interpret cosmic-ray air showers, thereby reducing systematic uncertainties in high-energy astrophysics.

Location and detector design: The apparatus was installed in the TAN region, about 140 meters from the ATLAS interaction point. It consists of two compact imaging calorimeters, Arm 1 and Arm 2, placed in the zero-degree neutral absorber region. Each calorimeter is a sampling device with layers of dense absorber and scintillating material that record electromagnetic showers from photons and neutral pions, with sufficient segmentation to identify two-photon decays.

Measurements and impact: LHCf collected data from proton–proton collisions at the LHC to determine energy spectra and spatial distributions of forward photons, neutral pions, and, to a lesser extent, neutrons. The results are used to tune hadronic interaction models, such as QGSJET, EPOS, and SIBYLL, which are employed in simulations of ultra-high-energy cosmic-ray events. The experiment provides benchmarks for forward-region particle production and helps calibrate air-shower models used in cosmic-ray physics.

Overview: LHCf represents a focused effort to connect collider measurements with astroparticle physics by delivering forward-region data essential for accurate modeling of cosmic-ray air showers.