The article describes a new measurement of the inelastic proton-air cross-section at a center-of-mass energy 57 TeV per nucleon. The cross-section is one of the basic quantities which characterize the nature of a two-particle collision. Its dependence on energy is connected to collision dynamics and the evolution of this dependence is sensitive to changes in the underlying collision mechanisms. The measurement of cross-section in interactions of cosmic ray protons with the atmosphere that was performed at the world-unique Pierre Auger Observatory is difficult to achieve, both methodically and experimentally. However, it allows us to get insight into collisions at energies far beyond the reach of accelerators. The published work describes in detail the systematic uncertainties of the measurement. The analysis of the data provides a value 505 ± 22 (stat)-36 +28(syst) mb (the unit milibarn = 10-31 m2). Using the Glauber theory, the result is converted to the cross-section of proton-proton collisions and compared to measurements at lower energies recently obtained from the experiments at LHC with center-of-mass energy of 8 TeV. The measurement is unique due to very high energy of collisions and particularly due to high precision of the result. It also demonstrates the way how the Pierre Auger Observatory contributes to resolving the problems of current particle physics, especially for the energy region far above beam energies currently available at present accelerator laboratories. Institute of Physics of the Academy of Sciences has been intensively participating in the Pierre Auger Observatory project already during construction phase. Our physicists operate the apparatus and take part in data analysis.
Comparison of inelastic proton-proton cross-section derived from data of the Pierre Auger Observatory (denoted as "This work") to model predictions and accelerator data.