Composition of cosmic rays at the extreme energies
Working group members :
- Serguei Vorobiov (Postdoc since 2004).
- Gilles Maurin (PhD Thesis in 2002-2005).
- Jacob Lamblin (Postdoc in 2003-2004).
- Dmitri Semikoz (Associated member (CNRS) since 2005).
Presentation of the research subject :The Auger project carried out by an international collaboration joining together 18 nations aims at detecting the cosmic rays of energy higher than 10^19 eV. The existence of these cosmic rays is a mystery to date. Indeed, to allow a cosmic ray of such ultra-high energy coming from an astrophysical source (supernovae, active galactic nuclei, radio-galaxy lobes, etc...) to be detected on Earth, several conditions must be fulfilled :
- these cosmic rays need to be accelerated to the energies higher than that detected. However, to our current knowledge, very few types of sources are able (after pushing the parameters of the models) to accelerate particles to these energies
- then they should avoid to lose a notable fraction of its energy (by radiation or interaction with the background radiation) while escaping from the source
- they should not lose too much energy during the time of its travel to the Earth.
Followed strategy :Study of the simulated events induced by protons, iron nuclei and photons:
- Simulation of atmospheric showers using CoRSiKa and Aires programs, and different nuclear interaction models (QGSJET/Sybill, GHEISHA/Fluka, ...).
- Rapid simulation of the Auger Surface Detector response to these showers.
- Definition of the first discriminating criteria and their application domain starting from simulated events.
- Comparison of criteria.
- Full detector simulation using different modules (Geant4, SDSim, ...) under Auger Data Processing and Analysis framework (DPA).
- Study of the discrimination criteria after event reconstruction.
- Study of the simulated signals (FADC traces recorded by Auger tanks) to be able to disentangle muonic component in the showers.
- Optimisation of discrimination criteria after reconstruction.
- Study of the robustness of the criteria with the various hadronic interaction models.
- Search for photons in the cosmic rays (eventual photon candidate events, photon flux limit, photon fraction limit, ...).
- Statistical discrimination analysis to establish the proportion in the ultra-high energy cosmic rays of lighter / heavier nuclei.
Results and public presentations :
- Upper limit on the primary photon fraction from the Pierre Auger Observatory: ICRC 2005
- Study of the nature of the ultra high energy cosmic rays starting from the first data of the Pierre Auger Observatory (in French): PhD Thesis of Gilles Maurin (2005)
- Poster presented at the "doctoriales" (PhD students formation stage) at Nice (in French): Doctoriales (2004)
- Presentation on the role of discrimination between primary particle species in the ultra-high energy cosmic rays (in French): JJC 2003 (2003)
- Presentation of discriminating criteria between primary particle species (in French): Vendredi PCC (2003)