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Theses

Search for cosmogenics photons in the ultra high energy cosmic ray flux

Abstract : Ultrahigh-energy cosmic rays (UHECRs), whose origin is still mysterious, provide a unique probe of the most extreme environments in the universe, of the intergalactic space and of particle physics beyond the reach of terrestrial accelerators. UHECRs are very scarce and their characteristics are inferred from the measurement of extensive air showers they produce.The Pierre Auger Observatory located in the province of Mendoza (Argentina) and covering 3000 square kilometres, brings unique capabilities to the UHECR study. It combines two techniques to measure the EAS properties by observing their longitudinal development in the atmosphere with the fluorescence detector (FD) consisting in 27 fluorescence telescopes, as well as their lateral spread at ground level with the surface detector (SD) consisting of 1660 autonomously operated water-Cherenkov detectors.The Pierre Auger Observatory started operating more than a decade ago. Outperforming preceding experiments both in size and in precision, it has boosted forward the field of UHECRs as witnessed by a wealth of results.But any harvest of new results also calls for new questions: what is the true nature of the spectral suppression: a propagation effect (so-called Greisen, Zatsepin and Kuz'min or GZK cutoff) or cosmic accelerators running out of steam? What is the composition of UHECRs at the highest energies? In order to answer these questions, the Auger Collaboration is undertaking a major upgrade program of its detectors, the AugerPrime project, designed to improve the knowledge on mass composition, mainly by discriminating electromagnetic and muonic shower components from SD-based observables, by having a further and independent measurement. Scintillator detectors will be settled on each of the 1660 Water Cherenkov detectors, with new electronics providing higher performances.The AUGER team of the LPSC assumes responsibilities in the in the monitoring and the follow-up of the performances of the SD, and contributes in an essential way to the project of improvement and renovation of the electronics. Furthermore, a part of scintillators will be assembled and tested in the LPSC in 2017.One of the main objectives of AugerPrime is the understanding of the suppression of the RCUHE flux at the highest energies. If it is the signature of propagation effect, the famous ' GZK ' effect, the detection of « cosmogenic » photons of ultra high energy can provide an independent evidence of the existence of this effect allowing to constrain the astrophysical scenarios. The lastest results from photon search in Auger data allowed to derive upper limits on the expected flux, at the level of the optimistic predictions of GZK models. The Observatory has no rivals in term of sensibility in UHE photon search, and with the future data, and the improvements brought to the detection, this sensibility will increase. The thesis work will consist mainly in data analysis to identify the air showers produced by UHE photons. New reconstruction methods and event selection procedures should be designed and implemented to exploit at best the detector performances.
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https://tel.archives-ouvertes.fr/tel-03144497
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Submitted on : Wednesday, February 17, 2021 - 4:29:29 PM
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  • HAL Id : tel-03144497, version 1

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STAR | IN2P3 | UGA | CNRS | LPSC

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Julien Souchard. Search for cosmogenics photons in the ultra high energy cosmic ray flux. Astrophysics [astro-ph]. Université Grenoble Alpes [2020-..], 2020. English. ⟨NNT : 2020GRALY030⟩. ⟨tel-03144497⟩

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