Development of the instrumentation and readout schemes of MARTA, an upgrade of the Pierre Auger Surface Detector
IDPASC Portugal - PHD Programme 2014
Instituto Superior Técnico
Laboratório de Instrumentação e Física Experimental de Partículas
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 Argentine 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 instrumentation of MARTA detectors. The candidate will develop the readout of the RPC detectors and test them during the deployment of a MARTA Engineering Array. The candidate is also expected to take part in the detector installation and commissioning. Each MARTA unit will consist of four RPCs, each with 64 pickup electrodes (pads). The signals coming from each pad must be amplified and recorded. The instrumentation system of MARTA must be able to record data from RPCs using a dual technique: Single Muon Counting using a simple threshold on each pad and Charge integration for high occupancy. The high number of acquisition channels implies that an ASIC should be used such as the MAROC chip, an identified candidate. Furthermore the system must be able to cope with the stringent requirements of a Cosmic Ray ground array detector: It must be able to work in a remote location, with minimal maintenance, must have a low cost per unit, present a good timing for data synchronization (~10ns) and must be able to consume low power (few Watt). The candidate will also work in cooperation with the Surface Detector Electronics group at Auger to discuss and implement the several interfaces and synchronization schemes.
January 01, 2015
July 29, 2020