Thesis

Electromagnetic Component of Extreme Energy Cosmic Rays Detected in Auger

• Call:

  IDPASC Portugal - PHD Programme 2014

• Academic Year:

  2014 /2015

• Domain:

  Astroparticle Physics

• Supervisor:

  Sofia Andringa

• Co-Supervisor:

  Bernardo Tomé

• Institution:

  Instituto Superior Técnico

• Host Institution:

  Laboratório de Instrumentação e Física Experimental de Partículas

• Abstract:

  The Pierre Auger Observatory aims at identifying the composition of primary cosmic rays and the sources which accelerate them to energies well above the ones achieved at Earth; but also at studying particle physics. In fact, at these energies, cosmic rays are not detected directly; the atmosphere acts as a calorimeter and an extensive air shower is produced by particle interactions at energies well above the LHC. The Observatory consists on a surface detector (SD) array, sampling the particles arriving at ground in an area of 3000 km² in the Argentinean Pampa, and a fluorescence telescopes detector (FD) imaging the longitudinal development of the electromagnetic component of the shower in the atmosphere, leading to an almost direct measurement of its primary energy and the position of shower maximum, which carries important information on the first interactions and primary particle type. The main advantage of the SD is that it has a 100% duty-cyle with contrast with a 10%-15% of the clear moonless nights in which the telescopes operate. However, its measurements are less direct and must be calibrated with hybrid events for which there are simultaneous measurements by the FD. The present ground stations are sensitive to both the electromagnetic and muonic components, but the Observatory plans to add an extra detector technology in order to improve the separation between both components. In this project we concentrate on the measurement and analysis of the electromagnetic component at ground. The hybrid data set will be used to characterize the signals at ground, and their dependence on primary energy and shower development parameters, as well as the detector station response. The relation between the lateral and longitudinal electromagnetic shower shapes will be explored to search for new observables which can be used in the analysis of ground-only data. One of our main goals is to extract an energy calibration independent of the muon content of the shower, decreasing the uncertainty due to its unaccounted fluctuations, and contributing to solve the “muon puzzle”. In fact, according to model predictions, extrapolated from much lower energy accelerator measurements, the present Auger SD results on muon content seem inconsistent with the results from the shower shape analyses in FD. Reconciling the muonic and electromagnetic shower components might be one of the best tests to particle interaction models at energies of 100 TeV.