Thesis

The Engineering Array of the MARTA detector for the upgrade of the Pierre Auger Observatory

• Call:

  IDPASC Portugal - PHD Programme 2014

• Academic Year:

  2014 /2015

• Domain:

  Astroparticle Physics

• Supervisor:

  Bernardo Tomé

• Co-Supervisor:

  Ruben Conceição

• Institution:

  Instituto Superior Técnico

• Host Institution:

  Laboratório de Instrumentação e Física Experimental de Partículas

• Abstract:

  The Pierre Auger Observatory, presently the world's largest cosmic-ray detector, detects the extensive air-showers (EAS) initiated by the interaction of ultra high energy cosmic rays (UHECR) in the Earth atmosphere at centre-of-mass energies up to 100 TeV, well above that of the LHC. The Observatory, located in the Argentinean Pampa, consists on a surface detector (SD) array of 1600 water Cherenkov tanks, sampling the shower secondary particles arriving at ground in an area of 3000 km² and a fluorescence telescopes detector (FD) imaging the longitudinal development of the electromagnetic component of the shower in the atmosphere. The data collected so far allowed to establish important breakthrough results at the highest energies: the suppression of the flux and hints of anisotropy of the cosmic rays arrival directions. Also, several possible scenarios for the origin of the UHECR were ruled out, favouring astrophysical acceleration mechanisms. Nevertheless, open questions remain to be solved, in particular about the origin and nature of the UHECRs. Currently, all under carried primary mass composition studies suggest either an unexpected astrophysical scenario or changes on the hadronic interaction physics at the highest energies. The answer to this puzzle implies a stronger knowledge about the shower physical mechanism, specially about the EAS muon content. This later quantity is directly related to the hadronic interactions that occur during the shower development and might help to break the current degeneracy of the shower observables between the primary mass composition and the hadronic interactions. The Auger Collaboration is presently studying different options for the upgrade of the detector to improve the air-shower measurement. In particular, the enhancement of the capabilities of the surface array for the identification of the muons produced in the EAS is a key aspect of the upgrade. In this context the LIP group is leading the MARTA project, proposing an innovative concept for the muon detection in Auger. MARTA (Muon Auger RPC for the Tank Array) consists basically of robust RPCs (Resistive Plate Chambers) deployed under the tanks of the SD array, that will measure the muons on an event-by-event basis with high efficiency, and high timing and spatial accuracy. These unique characteristics will further allow to measure simultaneously the muon signals in the tanks and in MARTA, providing a powerful tool to inter-calibrate both detectors and to monitor important parameters of the tanks. Several full scale prototypes are already installed and taking data in the Auger Observatory: a muon telescope, consisting of two RPCs placed on the top and the bottom of one tank, has been operating for several months at the Observatory; two MARTA stations are being deployed in the field and starting to take data. A MARTA Engineering Array (EA), consisting of about ten MARTA stations, will start to be deployed in the SD array during 2015. The successful operation of the EA will be of the utmost importance for the proof-of-concept of MARTA. The selected candidate will be involved in the activities of the LIP/Auger group, in particular those related with the Engineering Array. Performance and optimisation studies will be carried out by using state-of-the-art Monte Carlo simulations of the air-showers propagation and of the detectors at ground. The candidate is also expected to take part in the detector installation and commissioning. An important part of the work will consist in the analysis of the data taken by the EA and the comparison with the simulation results. This interplay between simulations and real data will be of great relevance both in the validation of the existing MARTA simulations and for possible improvements in the final detector design. Moreover, the first data of the EA can be also used to test our physical knowledge about the shower, as this array will collect mainly events with a centre-of-mass energy compatible with those of the most energetic man-made accelerator, the LHC. Therefore, the candidate is also expected to participate in the creation of tools to reconstruct showers.