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High Energy Interactions: From Colliders to Cosmic Rays

Final Report Summary - C2CR (High energy interactions: from colliders to cosmic rays)

The project has been devoted to the development of a new Monte Carlo (MC) model of hadronic and nuclear interactions taking into consideration non-linear interaction effects. A microscopic treatment of the latter has been developed in the framework of the Reggeon Field Theory, describing them by means of enhanced (Pomeron-Pomeron interaction) diagrams. A procedure for an all-order re-summation of the contributions of enhanced graphs has been developed, based on the corresponding Schwinger-Dyson equations.

The relative importance of various classes of enhanced diagrams has been investigated, comparing the contributions of the graphs of 'net'-like type and the ones of Pomeron 'loops'. It has been demonstrated that both kinds of diagrams provide important contributions to the elastic scattering amplitude and none of them can be neglected in the high energy limit. The calculated total and elastic cross sections appeared to be significantly (25 %-40 %) higher than earlier estimates which have been based on partial re-summations of restricted classes of enhanced graphs. On the other hand, the single high mass diffraction cross section was shown to saturate its growth well below the energy of the Large Hadron Collider (LHC).

Our approach has been applied for the development of a MC procedure for generating hadronic final state topologies and the developed algorithm has been implemented in the new version of the QGSJET MC model - QGSJET-II. The model parameters have been tuned based on available accelerator data, including the ones obtained recently at the LHC.

The model has been applied for calculations of extensive air shower (EAS) development. The predicted EAS characteristics have been compared to experimental data and the consequences for the nuclear composition of ultra-high energy cosmic rays (UHECR) have been deduced. The model has been included into EAS simulations programs CONEX and CORSIKA, thus making it available for public use in the cosmic ray field.

The QGSJET-II model has also been generalised to treat high energy photo-nuclear interactions, which made it applicable for studies of EAS induced by very high energy photons and for collider studies of photo-nuclear processes.

The model has been applied for a number of astrophysical problems, related to UHECR physics. A theoretical multi-messenger study of high energy radiation from the nearest active galactic nucleus, Centaurus A, allowed us to put constraints on the expected neutrino fluxes from the source and on the infra-red part of its spectral energy distribution. An investigation of possible gamma-ray signatures for UHECR acceleration in extra-galactic astrophysical sources has been performed, concentrating on the formation of gamma-ray 'halos' around the direction to the sources. The relations of the characteristics of the halos to the strength of the extra-galactic magnetic field ant to the maximal acceleration energy have been derived. A new program for treating the production of hadrons, photons, and neutrinos in astrophysical sources and for propagation of high energy particles through extra-galactic space has been developed, including a new efficient MC code for the development of electromagnetic cascades in the extra-galactic space.

The main result of the project has been the development of a new hadronic MC model, providing thereby a new instrument for experimental data analysis in cosmic ray and collider physics. The chosen strategy proved to be successful, the model being able to describe a variety of experimental data on hadronic production processes, with a relatively small set of adjustable parameters. The principal novelty of the model compared to earlier approaches is a self-consistent microscopic treatment of non-linear interaction effects: MC modelling of the interaction configurations is based on the partial cross sections for various final states, the latter being calculated taking all significant enhanced contributions into account.