List of PhD offers of laboratory.

Atlas
Etude des propriétés du boson de Higgs avec le détecteur ATLAS au LHC
PhD supervisor:
E. Monnier - +33 4 91 82 72 69 / +41 754 11 51 26 - monnier@cppm.in2p3.fr
Description:

English Version: Physics at the Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research) is the high priority research field of the Particle Physics community worldwide. ATLAS is one of the two general purpose experiments installed at the LHC that discovered a Higgs boson in July 2012, key piece for the understanding of the fundamental interactions and the origin of elementary particle mass. Its physics program extends beyond Higgs property measurements to the search for signs of physics beyond the Standard Model of particle physics.

The ATLAS group of the Centre de Physique des Particules de Marseille (CPPM) is deeply involved in this scientific program, in particular linked to its expertise of the electromagnetic calorimeter. The latter is a key component for the identification and energy measurement of electrons and photons, which were at the core of the Higgs boson discovery. It is also at the forefront of this boson studies and of the supersymmetry searches in the ongoing data taking campaign, so called Run 2, with major consequences in several analyses with leptons in their final states. Moreover, for the upgrade of the accelerator performances foreseen in 2021, this calorimeter has a major ongoing development program to dramatically upgrade its trigger and readout to which the CPPM group actively contributes.

In the Standard Model, the Higgs boson is highly coupled to the top quark, the known particle with the largest mass. The only way to directly measure this Higgs-top coupling (called top Yukawa coupling) is to observe the associated production of a Higgs boson with top quarks. This will be accessible for the first time with the Run 2 data that are taken since 2015 and until 2018. This key measurement, and more generally the Higgs properties studies are of high importance since they would allow to confirm that the observed boson is the Standard Model Higgs boson, or could reveal New Physics.

The goal of this thesis is on the one hand to exploit the Run 2 data set to get the best sensitivity on the Higgs property measurements and in particular the Yukawa coupling. The student will focus on the Higgs property measurement in multilepton final states (electron or muon). The Run 2 data taking conditions at the LHC (proton-proton collision center of mass energy increased to 13 TeV, high luminosity) are particularly suited for these measurements. The sensitivity to the sub-dominant Higgs production modes  particularly its associated production with top quarks  is increased, allowing for refined measurements of the Higgs boson properties. On the other hand and in parallel, the student will also contribute to the electromagnetic calorimeter upgrade, and in particular, to the study of its upgraded configuration, first exploiting data taken with a prototype installed for the 2018 data taking, then contributing to the installation and commissioning of its final system, and finally to its validation and performances assessment with the first Run 3 data in 2021.

In this framework, the student will have to do frequent stays at CERN and the research work will combine physics analysis on real and simulated data as well as studies and operation of experimental systems.

French Version: La physique auprès du Large Hadron Collider (LHC) du Centre Européen de Recherche Nucléaire (CERN) constitue aujourd'hui l'axe de recherche prioritaire de la communauté mondiale en physique des particules. ATLAS, l'une des deux expériences généralistes installées auprès de cet accélérateur, a découvert un boson de Higgs en juillet 2012, pièce essentielle pour la compréhension des interactions fondamentales et en particulier l'origine de la masse. Son programme de physique est néanmoins plus vaste et s'étend à l'étude des propriétés du boson de Higgs et plus généralement à l'obtention des premiers signes de physique au-delà du Modèle Standard de la physique des particules.

Le groupe ATLAS du Centre de Physique des Particules de Marseille (CPPM) est fortement impliqué dans ce programme scientifique, avec notamment une expertise liée au calorimètre électromagnétique. Ce dernier est un élément clé pour l'identification et la mesure de l'énergie des électrons et des photons, qui ont fait le succès de la découverte du boson de Higgs. Il est également en pointe sur l'étude de ce boson et la recherche de supersymétrie dans la campagne de prise de données actuelle, dite « Run 2 », avec des implications majeures dans plusieurs analyses avec des leptons dans l'état final. De plus, en vue de l'amélioration des performances de l'accélérateur prévue pour 2021, ce calorimètre fait l'objet d'un important programme d'évolution de son système de lecture et de déclenchement auquel participe activement le groupe du CPPM.

Dans le Modèle Standard, le boson de Higgs se couple préférentiellement avec le quark top, particule élémentaire la plus massive jamais découverte. Le seul moyen de mesurer directement ce couplage (dit couplage de Yukawa du top) est d'observer la production associée du Higgs avec des quarks top. Cela sera accessible pour la première fois avec les données du « Run 2 » qui sont prises depuis 2015 jusqu'en 2018. Cette mesure et plus généralement, l'étude des propriétés du boson de Higgs sont très importantes, car elles peuvent confirmer que le boson observé est bien le boson de Higgs du Modèle Standard ou pourrait révéler de la nouvelle physique.

Le sujet de cette thèse est d'une part d'exploiter la prise de données du « Run 2 » pour obtenir la meilleure sensibilité sur ces mesures des propriétés du boson de Higgs, en particulier sur la mesure du couplage de Yukawa. L'étudiant(e) axera son travail d'analyse sur la mesure des propriétés du boson de Higgs dans les états finals à plusieurs leptons (électrons ou muons). Les conditions de la prise de données « Run 2 » au LHC (énergie dans le centre de masse des collisions protons-protons accrue à 13 TeV, grande luminosité) sont particulièrement favorables pour ces mesures. En effet, la sensibilité aux productions sous-dominantes du boson de Higgs  notamment en association avec une paire de quarks top - est accrue, permettant des mesures plus fines des propriétés du boson de Higgs. D'autre part et en parallèle, l'étudiant contribuera au programme d'amélioration du calorimètre électromagnétique, et en particulier, étudiera ses performances dans sa configuration optimisée, d'abord en exploitant les données prises avec un prototype installé sur le détecteur pour la prise de données 2018, puis surtout en contribuant à l'installation et à la mise en uvre du système final et enfin à sa qualification et à l'établissement de ses performances avec les premières données du Run 3 en 2021. L'étudiant contribuera bien évidemment également au première prises de données de collision à parti du milieu 2021 et poursuivra ensuite leur analyse en 2022.

Dans ce cadre l'étudiant sera amené à effectuer de nombreux séjours au CERN, et son travail de recherche combinera des analyses de physique (sur données et simulation) ainsi que l'étude et la mise en uvre de systèmes expérimentaux.

Keywords:
Physique des particules
Code:
Doctorat-2023-AT-01
Development of artificial intelligence algorithms adapted to big data processing in embedded (FPGAs) trigger and data acquisition systems at the LHC
PhD supervisor:
Description:

Physics at the Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research) is the high priority research field of the Particle Physics community worldwide. ATLAS is one of the two general purpose experiments installed at the LHC that discovered a Higgs boson in July 2012, key piece for the understanding of the fundamental interactions and the origin of elementary particle mass. Its physics program extends beyond Higgs property measurements to the search for signs of physics beyond the Standard Model of particle physics. The upgrade of the LHC is a crucial part of the European strategy for particle physics. The second phase of the LHC upgrade will happen in 2025 and will increase by an order of magnitude the instantaneous luminosity leading to the High Luminosity LHC (HL-LHC). The increased luminosity puts more stringent requirements on the LHC detectors electronics and data processing. The ATLAS detector will undergo a major update to be adapted to the increasing luminosity at the HL-LHC, hence to the dramatic increase of produced data. In order to treat on the fly with advanced algorithm this huge amount of data (more than 500 Tb/s), we propose to deploy advanced technologies based on state-of-the-art digital electronics running AI algorithms.

Artificial Intelligence (AI) algorithms and machine learning techniques are nowadays one of the most expending fields in research and in the industry. The use of AI in experimental particle physics is not new but these algorithms are only used, for now, in later stages of data analysis such as the analyses leading to the recent discovery of the Higgs boson coupling to third generation quarks [1][2] for which the ATLAS group of the Centre de Physique des Particules de Marseille (CPPM) had a major contribution, namely the development of AI techniques for these analyses. For data acquisition and trigger applications, relatively simple algorithms are imbedded in the hardware to process on the fly the huge data flow in a timely manner. However, with the next generation of high-end Field Programmable Gate Arrays (FPGAs), that include large increase of available processing and memory units, it is becoming possible to implement complex AI algorithms inside these FPGAs and process on the fly big data flows with dramatically increased selection performance.

The ATLAS group of the Centre de Physique des Particules de Marseille (CPPM) is deeply involved in this scientific program, in particular linked to its expertise of the electromagnetic calorimeter. The latter is a key component for the identification and energy measurement of electrons and photons, which were at the core of the Higgs boson discovery. Moreover, for the upgrade of the accelerator performances foreseen in 2021, this calorimeter has a major ongoing development program to dramatically upgrade its trigger and readout to which the CPPM group actively contributes.

The main purpose of this project is to develop AI and machine learning techniques to dramatically improve big data processing effectiveness such the one needed in high pileup environment at the LHC. The main challenge is to efficiently implement these techniques into the dedicated data acquisition electronics, based on FPGAs, which are used for signal processing in particle physics detectors such as the ATLAS Liquid Argon (LAr) calorimeter and which are under development by the ATLAS CPPM group.

The signals from the LAr calorimeter are processed through a chain of electronic boards in order to extract the energy deposited in the calorimeter. The new electronic chain for the second phase of the LHC upgrade is described in [3]. An excellent resolution on the deposited energy and an accurate detection of the deposited time, in the blurred environment created by the pileup, is crucial for the operation of the calorimeters and of the full ATLAS detector to enhance its physics discovery potential. The computation of the deposited energy and timing is currently done using optimal filtering algorithms [4]. These filter algorithms are perfectly adapted for ideal situations with low noise. However, with the increased luminosity and thus the noise from pileup, the performance of the filter algorithms decreases significantly while no further extension nor tuning of those could recover the loss in performance.

AI algorithms have proven to be very powerful tools in data processing and provide the most interesting candidate to recover the performance of filter algorithms in high noise conditions. FPGAs, which are designed to efficiently treat a large amount of data in a very short time, are very much adapted to the online data processing needed at the LHC especially at the trigger level. FPGAs had, up to recently, relatively limited amount of computational resources, however high-end FPGAs have now enough resources to accommodate the needs of advanced AI and deep learning algorithms. This allows to combine the performance of AI algorithms with the speed and high bandwidth of the FPGAs to efficiently process the big data flow by electronic boards.

The backend electronic boards for the second phase of the upgrade of the LAr calorimeter (called LASP) will use the next high-end generation of FPGAs. Based on the unique skills and expertise present at CPPM in digital electronics, a prototype of these boards is currently being developed at CPPM and will be finalized in 2019. This prototype will be equipped with two high-end last generation FPGAs from INTEL/ALTERA (Worldwide leader in FPGA production and part of the INTEL group [5]). The research and development (R&D) program of these boards and their production is already financed as part of the government Très Grandes Infrastructures de Recherche (TGIR) program for the upgrade of the ATLAS detector. The aim of this project is to take advantage of this unique opportunity to develop the necessary tools enabling the embedding of AI algorithms on these boards and to further explore the outstanding capabilities opened by these developments for new applications. This can prove to be a breakthrough that can extend to many areas facing big data processing in particle physics, especially at the trigger level, and in the industry.

The objectives of this project can be divided into 6 main points: 1. Develop AI methods adapted to the specific problem of signal processing to compute the deposited energy in the calorimeter in high noise conditions. 2. Optimize these methods and compare them with the existing filter algorithms using simulated data that reflect the conditions of the LHC after the upgrade. 3. Adapt the algorithms for processing on FPGAs and optimize the needed processing power while keeping high performance. 4. Investigate and adapt the recent tools that are under developments for converting AI algorithms into HDL code that is used to program FPGAs. 5. Test the performance of the algorithms in-situ using the LASP board prototype currently under construction at CPPM. 6. Generalize the developed tools and study their wider usage for trigger processing and for applications outside the particle physics field including industrial applications.

Although this project is an experimental particle physics project, its reach extends to any field profiting from big data processing using AI algorithms on specific hardware such as FPGAs. This project provides a unique opportunity to enhance the multidisciplinary and industrial applications of the research and development programs at CPPM. Due to the promising industrial applications, a collaboration with Nexvision [6], a midsize company based in Marseille and leader in embedded civil security systems, is developed. Support from the Aix Marseille University Initiative of Excellence program, so-called AMIDEX, is already obtained for this project. Using the AMIDEX funding, a new postdoc has recently joined the CPPM group in January 2020 to work on this project for 2 years.

In this framework, the subject for this PhD project is to develop the needed AI algorithms with the CPPM group in close interaction with the postdoc. He will actively contribute to the study the performance of these algorithms after their implementation on FPGAs with the help of electronic engineers at CPPM. Finally, he will investigate the use of these algorithms for other applications particularly industrial applications of interest for Nexvision. During his thesis work, the student will have to go to CERN for short stays to interact with experts and regularly present his work. The research work will combine analysis on real and simulated data as well as studies and operation of experimental systems. Références bibliographiques:

[1] The ATLAS Collaboration, Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector, Phys. Lett. B 784 (2018) 173-191; arXiv:1806.00425

[2] The ATLAS Collaboration, Observation of H->bb decays and VH production with the ATLAS detector, Phys. Lett. B 786 (2018) 59-86; arXiv:1808.08238

[3] The ATLAS Collaboration, Technical Design Report for the Phase-II Upgrade of the ATLAS LAr Calorimeter, CERN-LHCC-2017-018, https://cds.cern.ch/record/2285582

[4] Cleland, W.E. and Stern E.G., Signal processing considerations for liquid ionization calorimeters in a high rate environment. NIM 338 p. 467. 1994

[5] ALTERA, world leading company in FPGA production recently acquired by INTEL, https://www.intel.com/content/www/us/en/products/programmable.html

[6] NEXVISION SAS, French company (based in Marseille) specialized in electronic reference design, https://nexvision.fr/

Keywords:
Physique des particules
Code:
Doctorat-2023-AT-03
Search for electroweak production of supersymmetric partciles at the LHC Run 3 with the ATLAS detector
PhD supervisor:
Steve Muanza - 04.91.82.72.75 - muanza@in2p3.fr
Description:

After the culminating triumph of the Standard Model (SM) in 2012 with the discovery of the Higgs boson by the ATLAS and CMS in the data collected at the LHC Run 1, the main focuses of these two experiments are the precision measurements of the Higgs boson properties and the pursue of direct signs of physics beyond the SM. We propose a PhD topic to continue to search for an electroweak (EW) production of supersymmetric (SUSY) particles at the LHC Run 3 with the ATLAS detector. At the Run 1 we participated to the irst ATLAS search for $pp\to\tilde\chi^{\pm}_{1}\tilde\chi^{0}_{2}\to W^{\pm}(\to\ell^{\pm}\nu)h^{0}_{125}(\to b\bar b)$ . We continued this search with the first data of Run 2 (L=36/fb from 2015-2016) and we are currently extending this search with the analysis of the full Run 2 dataset (L=140/fb) to search for $pp\to\tilde\chi^{\pm}_{1}\tilde\chi^{0}_{2}\to W^{\pm}(\to\ell^{\pm}\nu)Z^{0}(\to q\bar q/b\bar b)$ . Compared to the LHC Run2, Run 3 will have pp collisions reaching $\sqrt{s}=14$ TeV, the nominal center-of-mass energy of the LHC, and should collect an integrated luminosity of about 150/fb. Therefore the sensitivity to the signals should increase significantly and open new search channels like to vector boson production (VBF) mode of the above chargino-neutralino production. We intend to pursue the $pp\to\tilde\chi^{\pm}_{1}\tilde\chi^{0}_{2}\to W^{\pm}(\to\ell^{\pm}\nu)Z^{0}(\to q\bar q/b\bar b)$ signal and possibly to start explointing the VBF production of $pp\to\tilde\chi^{\pm}_{1}\tilde\chi^{0}_{2}\to W^{\pm}(\to\ell^{\pm}\nu)h^{0}_{125}(\to b\bar b)$ (accompanied by a forward jet and a backward jet). In addition to the increased center-of-mass energy and integrated luminosity, we'll continue to develop new approaches to the analysis that we are currently introducing in the $W+Z+mET$ analysis. All of these SUSY analyses he search topology is 1L+(2/3)jets+mET, where L and mET stand for charged lepton and missing transverse momentum, respectively. In the 1L+3jets+mET events (about half of the signal events), we designed a new method which distinguishes efficiently the initial-state-radiations from the final-state-radiations, and enables an improved reconstruction of the hadronic boson decay. Our aim is to combine this with existing algorithms that enables to split into two hemispheres the 2-vector contributions to the mET, so as to reconstruct completely the pattern of the SUSY decays. The selected student will take part into the data analysis of Run 3 as decsribed above. Prior to this, within his/her first year, he/she contribute to the studies of the performance of the jet flavour tagging algorithms used by the ATLAS collaboration.

Keywords:
Physique des particules
Code:
Doctorat-2023-AT-02
Belle II
Search for tau lepton flavour violating decays at Belle II
PhD supervisor:
Justine Serrano - 0033 4 91 82 72 80 - serrano@cppm.in2p3.fr
Description:

Being forbidden in the Standard Model (SM) of particle physics, lepton flavor violating decays are among the most powerful probes to search for physics beyond the SM. In view of the recent anomalies seen by LHCb on tests of lepton flavor universality in $b \to s$ and $b \to c$ processes, the interest of tau lepton flavor violating decays has been greatly reinforced. In particular, several new physics models predict branching fractions of $\tau\to\mu\mu\mu$ and $\tau\to\mu\gamma$ just below the current experimental limits.

The Belle II experiment located at KEK, Japan, has just started physics data taking, aiming at collecting 50 times more data than its predecessor, Belle, by 2027. Thanks to its clean environment and high $\tau^+ \tau^-$ cross section, it provides an ideal environment to study tau decays. The goal of this phD is to analyze the first Belle II data in order to obtain the best experimental limits on the lepton flavor violating decays $\tau\to\ell\ell\ell$ , where $\ell = e,\mu$ . Additional decays such as $\tau\to\ell\gamma$ or $\tau\to\ell h$ , h being a hadronic system, could also be studied.

This phD will take place at CPPM, Marseille (https://www.cppm.in2p3.fr/web/en/index.html). Travels to KEK for collaboration meetings, and longer stay for participation to the data taking, are foreseen.

The funding of this phD is provided by an ERC grant obtained by Justine serrano.
Contract Period : 36 months
Expected date of employment : 1 October 2020
Remuneration : 2135  monthly gross

Applicants must hold a Master degree (or equivalent) in Physics, or expect to hold such a degree by the start of employment. Application including a CV, grade records, a motivation statement and contacts of three possible persons to supply letter of recommendation should be sent by June 21st to Justine Serrano serrano@cppm.in2p3.fr.

References:
https://arxiv.org/abs/1808.10567
https://hflav-eos.web.cern.ch/hflav-eos/tau/spring-2017/lfv-limits-plot.html
https://arxiv.org/abs/1903.11517
https://arxiv.org/pdf/1806.05689.pdf

Keywords:
Physique des particules
Code:
Doctorat-1922-BE-01
HESS-CTA
Search for very-high-energy gamma ray and neutrino emission from microquasars with HESS and ANTARES/KM3NeT
PhD supervisor:
Description:

notice: this thesis project being shared between ANTARES/KM3NeT and HESS groups, the subject also appears in the KM3NeT section

Description of the thesis work:

Microquasars are binary objects comprising a compact object (mainly a black hole with a stellar mass or, in some cases, a neutron star) and a companion star (for example a giant blue star). The binary system is identified as a microquasar if the presence of relativistic jets is confirmed. Their X-ray emission has been studied in detail over the past two decades to characterize the X-ray emission cycles that trace the underlying physical phenomena: for example, the phases with material accretion followed by ejection in jets have typical signatures, in X-rays but also infrared and radio. The multi-wavelength aspect is thus fundamental for the understanding of these objects. The relative intensity of each type of radiation as well as their specific characteristics evolve during the cycle, some phases being potentially the place of very high energy emission.

Currently, the only microquasar possibly detected in very high energy gamma rays is Cygnus X-1,by MAGIC, in September 2007, associated with strong X-ray activity measured by the RXTE, Swift and INTEGRAL satellites. For some others sources, only upper limits on the flux of very high energy gamma rays have been estimated for binaries such as GRS1915+105, Circinus X-1, V4641Sgr, MAXI J1820+070.

HESS and Fermi will continue their operation at least up to 2022, taking more data to be analysed. The future CTA observatory, operating a hundred Cherenkov telescopes (99 in Chile and 19 on the island of La Palma), will start to be operational by 2022 and will improve the sensitivity by an order of magnitude above 100 GeV.

The transient jet phases are also interesting cosmic ray acceleration sites in the galaxy and, therefore for these sources, high-energy neutrinos may also be emitted. The detection of a neutrino signal is a smoking gun for the discovery of the sources of the high-energy cosmic rays. KM3NeT is the second-generation neutrino detector in the Mediterranean Sea. It will be distributed in two sites: a low energy site ORCA in France (5 GeV-10 TeV) and a high energy site ARCA in Italy (1 TeV-10 PeV). Both detectors will have a sensitivity largely improved compared to ANTARES at low and high energies. The deployment of the first detection lines has started in both detectors and data are ready to be analysed. Together with the KM3NeT data, we can combine them with the ANTARES dataset comprising more than 12 years of continuous data since 2007.

Expected studies to be performed by the candidate:

The Phd student will be a member of the HESS and ANTARES/KM3NeT Collaborations, he will then contribute to the search for VHE gamma-rays and neutrino emission from microquasars in the context of multi-wavelength and multi-messenger studies, with the aim of understanding the mechanisms in play in these systems, in terms of components and efficiency for the acceleration of high energy particles (especially modeling).

The work will essentially consist of data analysis and their interpretation. The most promising observation phases for the search for very high energy gamma and neutrino will be performed using X-rays, optical and radio data. It is a key step in particular for pointing telescopes. In particular, the Phd student will participate to the Target of Opportunity observations of binary systems by HESS, consisting in observations by HESS of X-ray binaries, on alerts built from data from other instruments. An estimation of the potential of the future observatories, CTA and KM3NeT, for the detection of galactic transient sources will be performed.

In the HESS Collaboration, the Phd student will participate to the calibration tasks, in particular concerning the recently upgraded telescopes, and will take part in the data taking in Namibia. In the KM3NeT Collaboration, the Phd student will also have to perform service tasks such as the participation to the calibration, the development of common software, real-time monitoring or analysis tools...

The candidate should therefore have a good background in astroparticle physics and astrophysics and interest in the data analysis. The analyses will be performed using C++, Root, and python on Linux platforms.

Keywords:
Astroparticules
Code:
Doctorat-2023-CT-01
KM3NeT
Measurement of neutrino oscillation parameters with early KM3NeT/ORCA data
PhD supervisor:
Jürgen Brunner - 0491827249 - brunner@cppm.in2p3.fr
Description:

KM3NeT/ORCA (Oscillation Research with Cosmics in the Abyss) is a deep sea neutrino telescope currently under construction at a depth of 2500m in the Mediterranean Sea off the coast of Toulon. ORCA is optimised for the detection of low energy (3-100 GeV) atmospheric neutrinos and will allow precision studies of neutrino properties. The first ORCA detection strings have been deployed in 2019. Currently the detector takes data with 4 of them. Two more detection strings will be installed soon.

The student will actively participate in the data taking of the ORCA detector and analyse those data. The goal of the thesis is to extract a clean signal of upgoing atmospheric neutrinos, to demonstrate that these data are affected by the phenomenon of neutrino oscillations and to measure the relevant oscillation parameters. Links: http://www.km3net.org http://www.cppm.in2p3.fr/rubrique.php3?id_rubrique=259

Keywords:
Physique des particules
Code:
Doctorat-2023-KM-02
Search for very-high-energy gamma ray and neutrino emission from microquasars with HESS and ANTARES/KM3NeT.
PhD supervisor:
Damien Dornic / Jean-Pierre Ernenwein - 04 91 82 76 82 - dornic@cppm.in2p3.fr ; ernenwein@cppm.in2p3.fr
Description:

Microquasars are binary objects comprising a compact object (mainly a black hole with a stellar mass or, in some cases, a neutron star) and a companion star (for example a giant blue star). The binary system is identified as a microquasar if the presence of relativistic jets is confirmed. Their Xray emission has been studied in detail over the past two decades to characterize the X-ray emission cycles that trace the underlying physical phenomena: for example, the phases with material accretion followed by ejection in jets have typical signatures, in X-rays but also infrared and radio. The multi-wavelength aspect is thus fundamental for the understanding of these objects. The relative intensity of each type of radiation as well as their specific characteristics evolve during the cycle, some phases being potentially the place of very high energy emission.

Currently, the only microquasar possibly detected in very high energy gamma rays is Cygnus X-1, by MAGIC, in September 2007, associated with strong X-ray activity measured by the RXTE, Swift and INTEGRAL satellites. For some others sources, only upper limits on the flux of very high energy gamma rays have been estimated for binaries such as GRS1915+105, Circinus X-1, V4641 Sgr, MAXI J1820+070. HESS and Fermi will continue their operation at least up to 2022, taking more data to be analysed. The future CTA observatory, operating a hundred Cherenkov telescopes (99 in Chile and 19 on the island of La Palma), will start to be operational by 2022 and will improve the sensitivity by an order of magnitude above 100 GeV.

The transient jet phases are also interesting cosmic ray acceleration sites in the galaxy and, therefore for these sources, high-energy neutrinos may also be emitted. The detection of a neutrino signal is a smoking gun for the discovery of the sources of the high-energy cosmic rays. KM3NeT is the second-generation neutrino detector in the Mediterranean Sea. It will be distributed in two sites: a low energy site ORCA in France (5 GeV-10 TeV) and a high energy site ARCA in Italy (1 TeV-10 PeV). Both detectors will have a sensitivity largely improved compared to ANTARES at low and high energies. The deployment of the first detection lines has started in both detectors and data are ready to be analysed. Together with the KM3NeT data, we can combine them with the ANTARES dataset comprising more than 12 years of continuous data since 2007.

Expected studies to be performed by the candidate: The Phd student will be a member of the HESS and ANTARES/KM3NeT Collaborations, he will then contribute to the search for VHE gamma-rays and neutrino emission from microquasars in the context of multi-wavelength and multi-messenger studies, with the aim of understanding the mechanisms in play in these systems, in terms of components and efficiency for the acceleration of high energy particles (especially modeling). The work will essentially consist of data analysis and their interpretation. The most promising observation phases for the search for very high energy gamma and neutrino will be performed using X-rays, optical and radio data. It is a key step in particular for pointing telescopes. In particular, the Phd student will participate to the Target of Opportunity observations of binary systems by HESS, consisting in observations by HESS of X-ray binaries, on alerts built from data from other instruments. An estimation of the potential of the future observatories, CTA and KM3NeT, for the detection of galactic transient sources will be performed.

In the HESS Collaboration, the Phd student will participate to the calibration tasks, in particular concerning the recently upgraded telescopes, and will take part in the data taking in Namibia. In the KM3NeT Collaboration, the Phd student will also have to perform service tasks such as the participation to the calibration, the development of common software, real-time monitoring or analysis tools...

The candidate should therefore have a good background in astroparticle physics and astrophysics and interest in the data analysis. The analyses will be performed using C++, Root, and python on Linux platforms.

Keywords:
Astroparticules
Code:
Doctorat-2023-KM-03
Real-time multi-messenger analysis with KM3NeT
PhD supervisor:
Damien Dornic, Vincent Bertin - 04 91 82 72 86 - dornic@cppm.in2p3.fr , bertin@cppm.in2p3.fr
Description:

Neutrinos are unique messengers to study the high-energy Universe as they are neutral and stable, interact weakly and therefore travel directly from their point of creation to the Earth without absorption. Nowadays, the sources of very high-energy cosmic rays are still unknown. The detection of a neutrino signal is a direct evidence of the sources and the proof of the hadronic mechanism that produced the cosmic rays.

KM3NeT is the second-generation neutrino detector in the Mediterranean Sea. It will be distributed in two sites: a low energy site ORCA in France (5 GeV-10 TeV) and a high energy site ARCA in Italy (1 TeV-10 PeV). Both detectors will have a sensitivity largely improved compared to ANTARES at low and high energies. The French site is located at 2500 m depth in the Mediterranean Sea, 40 km off Toulon close-by ANTARES. The infrastructure is already deployed in both sites and the first lines should be deployed by the end of 2018. The completion of the KM3NeT is expected to be achieved around 2023. High-energy neutrino physics is a young and an almost unexplored field, which owns much discovery potentials. IceCube, a complementary neutrino detector in the South Pole has already discovered the first cosmic neutrinos. This guaranties to have neutrino signal detections in KM3NeT.

The main goal of the thesis is to develop the real-time multi-messenger analysis in the two KM3NeT detectors to look for transient sources such as flares of blazar, gamma-ray bursts, fast radio bursts, supernovae To achieve this goal, the student will work in the development of the real-time analysis framework. The student will have to implement efficient selection of neutrinos over the atmospheric backgrounds. These neutrino streams can then be used to look for time and space correlation with external triggers from electromagnetic transients, gravitational waves and high-energy neutrinos. For the most interesting neutrinos, the student will also participate to the development of the alert sending system and the multi-wavelength follow-ups (radio, visible, X-ray and VHE). With this method, one neutrino could lead to a major discovery. In addition to the track event topology resulting from muon neutrino events, already exploited by ANTARES, KM3NeT event reconstructions will allow using cascade events (electron and tau neutrinos) with a quite good angular precision. As CPPM is the host lab of KM3NeT, the student will participate to the installation during sea campaigns, the calibration and the data analysis of the first lines. The candidate should therefore have a good background in astroparticle physics and astrophysics and interest in the data analysis. The analyses will be performed using C++, python and Root on Linux platforms.

[1] KM3NeT: http://www.km3net.org [2] https://www.cppm.in2p3.fr/web/fr/recherche/astroparticules/

Keywords:
Astroparticules
Code:
Doctorat-1922-KM-01
ENTER : Enhanced Neutrino Tagging and Energy Reconstruction
PhD supervisor:
Mathieu Perrin-Terrin - 04 91 82 72 59 - mathieu.perrin-terrin@cppm.in2p3.fr
Description:

Why does the universe contains matter? One of the keys to this question is the yet unknown CP violation in the neutrino sector and a world wide experimental effort is ongoing to measure this effect. Our group is exploring a novel experimental strategy to perform this measurement based on advanced beam tracker technologies installed at accelerator neutrino experiments with a far detector made of an extremely large submarine water cerenkov neutrino telescope.

The beam tracker is one of the keystones of this new approach. It allows to reconstruct individually the neutrinos at creation with excellent resolutions. Getting access to this information opens a new era in neutrino physics.

The principles of this technique can already be tested at the NA62 experiment at CERN. During the PhD, the student will participate to the data taking operations at CERN and will analyse the data with the aim to observe, for the first time (!), a $K^+ \to \mu^+ \nu$ decay with all three particles reconstructed.

In parallel, the student will participate to the characterisation of new high rate, time resolved silicon trackers.

Finally, the student will be involved in the design and simulation of an experiment based on the U70 accelerator in Russia sending a neutrinos beam to the KM3NeT-ORCA neutrino telescope in Marseille.

Keywords:
Physique des particules
Code:
Doctorat-2023-KM-01
LHCb
Search for New Physics via Lepton Flavor (Universality) Violation tests with purely leptonic very rare B decays with $\tau$ leptons in the final state
PhD supervisor:
Giampiero Mancinelli et Julien Cogan - 04.91.82.76.75 - giampi@cppm.in2p3.fr , cogan@cppm.in2p3.fr
Description:

The study of these modes is motivated by several anomalies which have been revealed somewhat recently in some experimental measurements, but also by phenomenological analyses. In fact, exciting, persistent hints of New Physics (NP) have shown up in analyses of rare B decays proceeding via flavor-changing neutral currents performed by LHCb and other experiments. All these measurements have received considerable attention as they provide deviations building up a tension at the 4-5$\sigma$ level with respect to the Standard Model (SM) and are currently the only indications of new physics coming from the CERN Large Hadron Collider (LHC) [1,2]. If none of these results is yet an evidence of NP, the picture they convey is impressively coherent. Their interpretations suggest consistently that: the heavy $\tau$ lepton should be more affected by NP than the lighter $e$ and $\mu$ leptons; the $b \to s \tau \tau$ transition could be enhanced up to 3 orders of magnitude with respect to the SM predictions; NP appears not to respect the SM paradigm of Lepton Flavor Universality, leading in many models to a Violation of Lepton Flavor as well, with measurable rates for and $b \to s \tau \mu$ transitions.

Lepton Flavor (Univerality) Violation is hence becoming an extremely hot topic on which LHCb should be able to shed light in the forthcoming years. The very rare decays of $B_(s)$ mesons into $tau$ leptons are key channels to indirectly constraint the new physics phase space[3], though extremely difficult to study.

The LHCb experiment, one of the four large experiments operating at the LHC, is dedicated to heavy flavor physics. During the LHC Run I and II, it has collected about 9 fb$^{-1}$ of proton-proton interactions, gathering the largest sample of B mesons ever recorded, and thus it is a unique place to look for rare or forbidden decays.

After taking a leading role in the first observation of the $B^0_s \to \mu^+ \mu^-$ decay, after a 20 years search (published in Nature in 2015 [4]), the LHCb team has published the first limit on $B^0_s \to \tau^+ \tau^-$ in 2017 [5] and has presented a soon to be published first result ever for the $B^0_s \to \mu \tau$ mode [6] with the Run I data. This last results is on the verge of excluding (or otherwise confirm) some of the most promising models with Leptoquarks explaining the above-mentioned anomalies. The goal of this thesis is to improve and optimize the analysis technique and strategy for these modes while exploiting the full LHCb data-set as well as the development of new reconstruction algorithms.

References: (1) arXiv:1704.05340 (2) Eur. Phys. J. C (2017) 77: 377 (3) arXiv:1903.11517 (4) arXiv:1411.4413 (5) arXiv:1703.02508 (6) arXiv1905.06614

Keywords:
Physique des particules
Code:
Doctorat-2023-LH-01
Searches for effects beyond the Standard Model in semileptonic decays of B mesons at LHCb
PhD supervisor:
Anton Poluektov - 04.91.82.72.60 - poluektov@cppm.in2p3.fr
Description:

The Standard Model of particle physics, the theory that combines all the known fundamental forces of nature apart from gravity, has been so far very successful in describing all the present experimental data in particle physics. However, observations in cosmology, such as existence of Dark Matter or matter-antimatter asymmetry in the Universe, suggest that the Standard Model is not yet complete.

Hints on violation of lepton flavour universality seen in the studies of beauty hadron decays are some of the strongest and most intriguing evidences for the effects of physics beyond the Standard Model. The LHCb experiment at the LHC collider at CERN is dedicated to studies of beauty hadron decays, and the research group at CPPM has been actively involved in these studies. Currently, LHCb is undergoing a major upgrade, which will allow it in a few years from now collect unprecedented data samples and bring these measurements to a new level of precision.

The candidate will join the LHCb experiment group at CPPM and will play an active role in the programme of analyses using decays of beauty hadrons into the final states with a single tau lepton at LHCb (so-called semileptonic decays which occur due to charged weak current transitions). The aim of these studies is to search for effects beyond the Standard Model in the measurements of lepton flavour universality, angular distributions, and charge-parity (CP) violation in these decays.

During the PhD project, the candidate will develop the procedures to reconstruct the kinematic properties of the decays of beauty mesons into the final states with a tau lepton and a tau neutrino. (S)he will perform the studies of kinematic distributions of the decay products and CP asymmetries in these decays, which may show signs of effects beyond the Standard Model.

In addition to the activities in physics analysis, the candidate will participate in the development of particle identification calibration techniques at LHCb, both with the currently available data and for the ongoing upgrade as a part of our involvement in the LHCb Real-Time Analysis (RTA) project.

Keywords:
Physique des particules
Code:
Doctorat-1922-LH-01
Renoir
Constraining dark energy parameters or probing new cosmology with the LSST supernova dataset
PhD supervisor:
Dominique Fouchez - 04 91 82 76 49 - fouchez@cppm.in2p3.fr
Description:

Twenty years after the discovery of the current acceleration of the expansion of the universe by supernova measurements, the supernova probe remains the most accurate way to measure the parameters of this recent period in the history of our universe dominated by the so-called dark energy.

The precision measurements that can be performed by the supenova probe will be a crucial element that, in combination with other probes (LSS, weak lenses, CMB, etc.), will put strong constraints on the nature of dark energy. This will be made possible by the exceptional Supernova data set to be provided by LSST, with a combination of huge statistics and extreme calibration accuracy. The Large Synoptic Telescope (LSST) project will be launched in 2021 and will be commissioned in 2021. at full speed by the end of 2022. It is an 8.4-metre telescope with a 3.2 billion pixel camera, the most powerful ever built. This telescope will take a picture of half the sky every three nights for ten years. This survey will make it possible to measure billions of galaxies with great accuracy and to track the variation over time of all transient objects. With many other astrophysical studies, it will be a very powerful machine for determining cosmological parameters using many different probes and, in particular, it will impose strong constraints on the nature of dark energy. The LSST project aims to discover up to half a million supernovae. This two to three orders of magnitude improvement in statistics over the current data set will allow accurate testing of dark energy parameters and will also impose new constraints on the universe's isotropy.

In this PhD, we propose to prepare and participate in the first analysis of the data of the LSST supernova. The preparation will be carried out by working on the precise photometric measurement and photometric selection of the type Ia supernova. These two points are among the most important sources of systematic errors and all work to reduce and mitigate these sources of error will have a significant impact on the final measurement. The CPPM LSST group is already engaged in precision photometry work for LSST with direct involvement in algorithm validation within DESC/LSST [1][2][3] and has proposed a new deep learning method to improve the photometric identification of supernovae [4] and photometric redshifts [5]. The doctoral student will work within this framework by applying a complete analysis pipeline built with these tools, which he/she will contribute to improving, to the precursor data currently available: SNLS, SDSS, DES and HSC to validate his/her work, and will then have access to the first LSST images and supernova detections to participate in the first analysis of the LSST supernova data set.

The CPPM cosmology group is also involved in the DESI and Euclid surveys and collaborates with theorists to study alternative cosmological models, so that extensions of doctoral candidates' work can be found by combining the data with these other surveys and/or by testing a new cosmology through these new supernova data measurements.

[1] https://www.lsst.org/content/lsst-science-drivers-reference-design-and-anticipated-data-products

[2] https://arxiv.org/abs/1211.0310

[4] https://arxiv.org/abs/1901.01298

[5] https://arxiv.org/abs/1806.06607

Keywords:
Cosmologie observationnelle
Code:
Doctorat-2023-RE-02
Void lensing as a test of gravity in the DESI data
PhD supervisor:
Stéphanie ESCOFFIER - 04 91 82 76 64 - escoffier@cppm.in2p3.fr
Description:

Scientific context of the project Voids are very low-density environments in the large-scale distribution of matter in the Universe. As they are nearly devoid of matter, voids constitute a promising new probe for testing cosmological models and theories of gravity (Baker et al. 2018; Cai 2018; Hamaus et al. 2016). With the tremendous progress of large galaxy surveys in recent years, the study of cosmic voids has entered the observational domain of precision cosmology (Lavaux and Wandelt 2012).

Following on clustering studies applied to cosmic voids, as Alcock-Paczynski effect (Hamaus et al. 2016; Sutter et al. 2012) and redshift-space distortions (RSD) around voids (Hamaus et al. 2017; Hawken et al. 2017), a powerful approach consists in cross-correlating cosmic voids with weak-lensing (WL) or cosmic microwave background (CMB). Recently the Dark Energy Survey collaboration has published results on the weak-lensing and ISW imprints of voids obtained from photometric galaxy catalogs (Kovács et al. 2019; Sanchez et al. 2017). Indeed, the measurement of weak gravitational lensing probes matter inhomogeneities in the Universe through the deflections of the light of background sources.

Although the weak lensing measurements are widely performed to map matter overdensities, it has been shown that they should be affected by underdensities in the matter distribution as well (Amendola, Frieman, and Waga 1999). The key point is that underdense regions like cosmic voids are more subject to differences between dark energy and modified gravity models due to the screening mechanism of the hypothetical fifth force (Baker et al. 2018).

However, as the tangential shear signal is expected to be very small for individual voids, theoretical calculations (Krause et al. 2013) and numerical simulations (Higuchi, Oguri, and Hamana 2013) suggest that stacking many voids will enhance the significance of the lensing measurement. In addition, the stacked weak lensing signal from voids is a direct measurement of the void density profile which can be used to constrain cosmological models without requiring any assumption about the galaxy bias. The recent lensing measurement with 87 cosmic voids from DES-SV data is very encouraging with a 4? significance (Sanchez et al. 2017), which confirms that measurements that will be obtained with spectroscopic surveys should provide stronger constraints on modified gravity models.

With the imminent massive influx of cosmological data like the DESI ground-based dark energy experiment, the number of observed objects is expected to be at least one order of magnitude. Indeed, the DESI instrument will conduct a five-year survey designed to cover 14,000 deg2 and to map the large-scale structure of the Universe from redshift 0 to 3.5 by measuring 34 million redshifts (Aghamousa et al. 2016). The expected number of voids is several tens of thousands. The DESI project will begin the survey in June 2020 after 4 months of Survey Validation. At CPPM we were involved in the construction and testing of the 10 DESI spectrometers. We are full member of DESI with guaranteed access to the DESI private data.

Description of the thesis work The aim is to apply this kind of analysis on the DESI spectroscopic data, using DESI photometric surveys used for DESI targeting (DECALs). In addition, we propose to constrain the velocity distribution around the same voids via redshift-space distortion (RSD) measurements. The combination of these two methods will allow implications on competing models of gravity and dark matter from a yet unexplored domain of the cosmic web. This approach is particularly timely, as lensing and RSDs around voids have only recently been detected individually, but have never been analyzed jointly.

Keywords:
Cosmologie observationnelle
Code:
Doctorat-2023-RE-03
Contraintes cosmologiques par analyse tomographique du BAO avec Euclid
PhD supervisor:
Stéphanie Escoffier / William GILLARD - 491827667 - gillard@cppm.in2p3.fr
Description:

(English bellow)

Les diverses observations de l'Univers indiquent depuis vingt ans maintenant que l'expansion de l'Univers est accélérée. Le modèle standard de la cosmologie, dit modèle LCDM, décrit l'Univers comme composé de 27% de matière noire et de 68% d'énergie noire. Comprendre la nature de ces deux composantes énergétiques demeure l'un des plus grands défis de la physique contemporaine.

Depuis la dernière décennie, les grands sondages spectroscopiques de galaxies ont joué un rôle majeur, en particulier avec l'étude de l'échelle des oscillations acoustiques baryoniques (BAO) mesurée dans la distribution des galaxies, comme dans SDSS (Alam et al. 2016; Anderson et al. 2014; Eisenstein et al. 2005), WiggleZ (Blake et al. 2011) ou 6dFGS (Beutler et al. 2011). La signature de l'empreinte BAO peut également être mesurée dans des sondages purement photométriques, comme dans le Dark Energy Survey (DES) (Abbott et al. 2019). La difficulté principale est que les redshifts photométriques sont beaucoup moins précis que ceux obtenus par spectroscopie, ne permettant pas de mener des analyses de clustering dites tridimensionnelles. La mesure est alors réalisée à l'aide de la fonction de corrélation angulaire w ou du spectre de puissance angulaire Cl dans plusieurs tranches de redshift (méthode de tomographie).

Le sujet de la thèse proposée est de mesurer l'échelle BAO par une analyse tomographique sur les données photométriques et spectroscopiques d'Euclid. Euclid est la mission spatiale dédiée à l'étude de l'énergie noire et de la matière noire dans l'Univers. Euclid a été sélectionné par l'Agence Spatiale Européenne (ESA) en 2011 et sera lancé en 2022 pour sonder l'Univers pendant 6 ans. Deux instruments seront embarqués à bord d'Euclid, un imageur dans le domaine visible, l'instrument VIS, qui permettra d'observer des milliards de galaxies, et un spectrophotomètre dans le domaine infrarouge, l'instrument NISP, qui mesurera le spectre de 50 millions de galaxies sur un domaine en redshift de 1

La première étape du travail de thèse consistera à calibrer les redshifts photométriques (photo-z) d'Euclid à partir de l'échantillon spectroscopique. Cette étape se fera dans un premier temps à partir de la simulation Flagship d'Euclid qui contient plus de 3 millions d'objets. Puis il s'agira de développer les outils de clustering angulaire afin d'extraire le signal BAO à partir de l'échantillon photométrique, ainsi qu'à partir de l'échantillon spectroscopique par analyse tomographique. Cette analyse requiert d'optimiser la chaine de traitement afin de pouvoir traiter plus d'un millier de mocks pour le calcul des matrices de covariance. Les effets systématiques comme l'influence de la cosmologie fiducielle, les erreurs photo-z, les biais seront attentivement étudiés. La dernière étape sera d'appliquer toute la chaine d'analyse sur les données Y1 d'Euclid.

Cette thèse pourra être précédée d'un stage niveau Master 2. Un financement CNES sera demandé pour cette thèse.

____________________________________________________________________

Title: BAO measurement from angular clustering with photometric and spectroscopic Euclid data

Since the last twenty years, various observations indicate that the expansion of the Universe is accelerated. The standard model of cosmology, called the LCDM model, describes the Universe as composed of 27% of dark matter and 68% of dark energy. Understanding the nature of these two energy components remains one of the greatest challenges of contemporary physics.

Since the last decade, large spectroscopic galaxy surveys have played a major role in the study of these components through measurement of the scale of the baryonic acoustic oscillations (BAO) that is measured in the distribution of galaxies: SDSS (Alam et al., 2016 Anderson et al., 2014, Eisenstein et al., 2005), WiggleZ (Blake et al., 2011) or 6dFGS (Beutler et al., 2011). The signature of the BAO footprint can also be measured with purely photometric probes, as in the Dark Energy Survey (DES) (Abbott et al., 2019). The main difficulty is that the photometric redshifts are much less precise than those obtained by spectroscopy, not allowing to conduct so-called three-dimensional clustering analyzes. The measurement is then performed using the angular correlation function or the angular power spectrum in several redshift slices so called tomography method.

The subject of the proposed thesis is to measure the BAO scale by a tomographic analysis on the photometric and spectroscopic data of Euclid.

Euclid is the space mission dedicated to the study of dark energy and dark matter in the Universe. Euclid was selected by the European Space Agency (ESA) in 2011 and will be launched in 2022 to probe the Universe for 6 years. Two instruments will be aboard Euclid, an visible imager the VIS instrument, which will allow to observe billions of galaxies, and a near-infrared spectrophotometer, the NISP instrument, which will measure the spectrum of 50 million galaxies on a redshift domain of 1

The first step of the PhD work will be to calibrate Euclid's photometric redshifts (photo-z) from the spectroscopic sample. This step will be done initially from Euclid's Flagship simulation which contains more than 3 million objects. Then we will develop the angular clustering tools to extract the BAO signal from the photometric sample, as well as from the spectroscopic sample by tomographic analysis. This analysis requires the optimization of the processing chain in order to process more than a thousand mocks for the calculation of covariance matrices. Systematic effects such as the influence of fiducial cosmology, photo-z errors, biases will be carefully studied. The final step will be to apply the entire chain of analysis to the first year of the Euclid data.

Références bibliographiques :

Abbott, T. M. C. et al. 2019. Dark Energy Survey Year 1 Results: Measurement of the Baryon Acoustic Oscillation Scale in the Distribution of Galaxies to Redshift 1. Mon.Not.Roy.Astron.Soc. 483(4): 486683.

Alam, S. et al. 2016. The Clustering of Galaxies in the Completed SDSS-III Baryon Oscillation Spectroscopic Survey: Cosmological Analysis of the DR12 Galaxy Sample. Mon.Not.Roy.Astron.Soc. arXiv:1607.03155 [astro-ph.CO] |.

Anderson, L. et al. 2014. The Clustering of Galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Baryon Acoustic Oscillations in the Data Release 10 and 11 Galaxy Samples. Month. Not. Royal Astron. Soc. 441: 24-62.

Beutler, Florian et al. 2011. The 6dF Galaxy Survey: Baryon Acoustic Oscillations and the Local Hubble Constant. Monthly Notices of the Royal Astronomical Society 416: 301732.

Blake, Chris et al. 2011. The WiggleZ Dark Energy Survey: Mapping the Distance-Redshift Relation with Baryon Acoustic Oscillations. Monthly Notices of the Royal Astronomical Society 418(3): 170724.

Eisenstein, Daniel J. et al. 2005. Detection of the Baryon Acoustic Peak in the Large-Scale Correlation Function of SDSS Luminous Red Galaxies. The Astrophysical Journal 633: 56074.

Laureijs, R. et al. 2011. Euclid Definition Study Report. arXiv:1110.3193.

Keywords:
Cosmologie observationnelle
Code:
Doctorat-2023-RE-01
Etalonnage photométrique à la précision du millième du relevé LSST à l'aide des données de GAIA
PhD supervisor:
Fabrice Feinstein - 04 91 82 72 83 - feinstein@cppm.in2p3.fr
Description:

L'accélération de l'expansion de l'Univers a été découverte il y a vingt ans, grâce à l'utilisation des supernovas de type Ia (SN Ia) comme chandelles standards. Le constituant responsable de cette accélération, qui représente 68 pour cent de la densité de l'Univers, a été appelé énergie noire. Ce phénomène qui domine la dynamique de l'expansion reste cependant énigmatique.

Le CPPM propose un sujet de thèse sur l'exploitation des données photométriques et spectro-photométriques du satellite GAIA pour l'étalonnage ultra-précis du futur Large Synoptic Survey Telescope (le LSST). Par son ampleur (la moitié de la voute céleste couverte, tout le ciel observé chaque deux semaines) et la précision de son instrumentation, le LSST va révolutionner notre connaissance de la cosmologie. L'équipe du CPPM qui prépare l'analyse du LSST est constituée de deux permanents et de trois jeunes chercheurs. Comme les autes membres de l'équipe, le candidat rejoindra la Dark Energy Science Collaboration (DESC), associée au LSST, qui se réunit aux Etat-Unis deux fois par an.

Le LSST observera plusieurs dizaines de milliers de SN Ia dans les conditions optimales d'un instrument de photométrie de précision sur le ciel du Chili. Ces observations permettront de construire un diagramme de Hubble avec une statistique de SN Ia 20 à 100 fois supérieure à celle des diagrammes actuels qui en contiennent 700. Pour tirer le meilleur parti de cette statistique, il convient d'obtenir une précision photométrique de l'ordre de 1 pour mille. Cette précision est nécessaire pour limiter les biais dans la détermination de la distance lumineuse des SN Ia et de leur galaxie hôte.

Les meilleurs relevés photométriques au sol obtiennent actuellement une précision de l'ordre de 5 pour mille. Dans cette thèse, nous allons tirer parti des données du relevé spatial GAIA. Ses données photométriques et spectrophotométriques ne sont pas affectées par l'atmosphère et couvrent l'ensemble de la voute céleste avec un instrument stable. Au CPPM, nous développons des méthodes et des outils de simulation qui s'ancreront sur les résultats de GAIA, afin de corriger la variabilité des observations de LSST. Cette variabilité provient d'une part de l'absorption de l'atmosphère plus ou moins humide et chargée en poussière au cours des nuits et des saisons. D'autre part l'instrument lui-même varie avec le temps : gain de la caméra, rélectivité des miroirs, etc.

Il s'agit donc de développer et de tester sur des simulations, des méthodes d'analyses qui tirent parti des centaines de millions d'étoiles stables qui seront observées en commun par GAIA et LSST. En plus des moyens communs à tous les laboratoires de l'Institut National de Physique Nucléaire et de Physique des Particules (IN2P3), comme le centre de calcul de Lyon, le candidat aura accès à un calculateur dédié installé au CPPM, de type HPC, équipé de 800 curs et de 500 à 1500 GB de RAM. Cette machine est particulièrement adaptée aux développements de telles méthodes.

Le calendrier de la thèse (2019-2022) permettra de tirer parti de GAIA qui a déjà des résultats et de tester les méthodes d'étalonnage de la photométrie du LSST sur les premières observations qui débuteront en 2020. A l'issue de sa thèse, le candidat sera en excellente position, au sein de DESC, pour contribuer fortement à l'analyse des premières SN Ia de LSST qui donneront, sur l'accélération de l'expansion, des résultats déjà compétitifs avec ceux des relevés précédents.

Keywords:
Cosmologie observationnelle
Code:
Doctorat-1922-RE-01
imXgam
Développement d'un cristal « scintronique » pour les applications d'imagerie ultra-rapide de rayons gamma
PhD supervisor:
Christian Morel - 0491827673 - morel@cppm.in2p3.fr - - - -
Description:

Le projet ClearMind a pour but de développer un détecteur monolithique de rayons gamma (0.5 MeV à quelques MeV) de grande surface (<= 25 cm2), de grande efficacité et de hautes résolutions spatiale (< 4 mm3 FWHM) et temporelle (< 20 ps FWHM) dans le but d'améliorer les performances des tomographes à émission de positons à temps-de-vol (TOF-TEP), mais aussi la réalisation de caméras Compton innovantes utilisées comme gamma-caméras pour l'imagerie des gammas prompts en hadronthérapie et de la radioactivité lors d'opérations de démantèlement nucléaire.

Ce détecteur sensible à la position est constitué d'un cristal scintillant sur lequel est directement déposée une couche photoélectrique d'indice de réfraction supérieur à celui du cristal. Ce cristal « scintronique », qui allie scintillation et génération de photoélectrons, permet d'optimiser la transmission des photons de scintillation et des photons de lumière Cherenkov à la couche photoélectrique. Par rapport aux montages classiques, un gain d'un facteur 4 sur la probabilité de transmission des photons optiques entre le cristal et la couche photoélectrique est attendu. Le cristal sera encapsulé avec un tube multiplicateur à galette de micro-canaux (MCP-MT) afin d'amplifier le signal et d'optimiser le temps de transit des photoélectrons vers le plan d'anodes de détection (densément pixélisé) et ainsi les résolutions temporelle et spatiale de la chaîne de détection. L'objectif de la thèse est de participer au développement et à la caractérisation de ce module de détection en collaboration avec l'IRFU à Saclay, de le modéliser avec l'outil de simulation Monte Carlo GATE dans le but d'évaluer l'impact de cette nouvelle approche sur les performances d'un imageur TOF-TEP, et à terme corps entier.

Keywords:
Instrumentation
Code:
Doctorat-1922-IM-01