Project
Participação portuguesa no Observatório Pierre Auger

Code CERN/FIS-PAR/0023/2017

Beneficiary Entity

LIP - Laboratório de Instrumentação e Física Experimental de Partículas

Project summary

The main goal of this proposal is to develop the measurement capabilities of the Pierre Auger Observatory, focusing mainly on the muonic component of Air Showers. This is pursued through the commissioning of MARTA – an innovative detector concept to measure the muon content directly - and by increasing the precision of the knowledge of the standard Auger detectors. The proposal builds upon CERN/FIS-PAR/0034/2019 and has a strong synergy with the proposal CERN/FIS-PAR/0020/2021, which is dedicated to the higher-level (shower level) data analysis and interpretation of the results.Auger was built to give a significant contribution to the understanding of ultra-high energy cosmic rays (UHECR), their origin and nature, as well as to study particle interactions at such high energies. Today, nearly 500 physicists are part of the collaboration. The Observatory, in Argentina, had its construction completed in 2008 and the covered area of ~ 3000 km2 allowed to have unprecedented statistics. Its hybrid nature, i.e. the simultaneous measurement through the fluorescence technique and the particle sampling at the ground, allowed to lower the experimental systematic uncertainties dramatically.The data taken by Auger led to several breakthroughs in UHECR physics. A suppression of the CR flux above 5.5x10^19 eV is firmly established, and the fine structure of the spectrum starts to unveil. A dipolar asymmetry on the arrival directions has been observed, strongly supporting their extra-galactic origin. The CR composition at very high energies has been inferred from shower measurements, and its interpretation indicates an unexpected transition from proton to heavier elements above 3x10^18 eV. The collaboration has also a research program to estimate the hadronic interaction properties at the highest energies. One of the most intriguing results from this research area is the apparent muon deficit in predictions. Additionally, no hadronic interaction model can explain all the measured shower observables simultaneously.The impact of Auger on the UHECR field has been tremendous. The collaboration published around 150 papers that have already more than 16000 citations (source: inspire), including seven articles ranked among the most cited in PRL, Astropart. Phys. and NIMA.The obtained results present either an unexpected astrophysical panorama or even new physics at the highest energies. However, the above claim gets significantly undermined by the poor control over the shower description, i.e. over our understanding about hadronic interactions. This puts pressure on the study of the shower muonic component. Muons stem directly from the decay of charged mesons and can travel long distances being able to reach the ground. They are thus a direct link to the hadronic interaction activity within the shower.Auger has set up an upgrade program to increase the collected information for each shower. The core of the upgrade is the installation of a scintillator detector on top of each Water Cherenkov Detector (WCD). This will give information about the different components of the showers, increasing the mass composition sensitivity. Besides, in a limited part of the array, near the WCD, buried scintillators will be installed to grasp the muon component. In this context, LIP is responsible for the installation of MARTA, a small array of RPCs under the WCD to perform a direct measure of the muons present at the stations. MARTA high-quality data will enable cross-calibrations between different detectors and will be able to deliver physics muon measurements at E = 10^17 eV, which corresponds to the LHC centre-of-mass energy. Such measurements would allow giving input to high-energy hadronic interaction models and shower simulation packages.In the preceding grant, the field was prepared to receive detectors and the first prototype was deployed. Unfortunately, the pandemia made impossible the commissioning of the station. Work proceeded on the development of several tools for simulation and analyses of MARTA.The main objective of the proposal is the commissioning and data exploitation of MARTA, which requires a strong presence in Argentina. We will also continue R&D in RPC detectors and DAQ systems to enhance the detection capabilities of MARTA and to develop by-products such as muon hodoscopes, to study in detail the response of the other detectors in Auger.This research program will give a major contribution to the mitigation of systematic uncertainties at Auger, allowing to study the early shower development further. The successful operation of these novel detectors will also pave the way for RPCs to become a standard technology in the field, providing affordable high-resolution detection of the shower front. The research program is organized in five main tasks: MARTA commissioning and Monitoring; Detector R&D; MARTA simulation and data analysis; Auger Detector Performance & Calibration; Outreach.

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Support under

Reforçar a investigação, o desenvolvimento tecnológico e a inovação

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