Liste des offres de thèses du laboratoire.

Atlas
Search for electroweak SUSY production with ATLAS detector at LHC Run 3 and developments of b-tagging algorithms for LHC Run 4
Directeur de thèse :
Steve Muanza - 04 91 82 72 75 - muanza@cppm.in2p3.fr
Description :

The highlight of the LHC so far has been the discovery of the Higgs boson by the ATLAS [1] and CMS [2] collaborations at the LHC Run 1 (2010-2012).

Surprisingly, after most of the LHC Run 2 (2015-2018) data have been analyzed, at the high energy frontier, covered by both ATLAS and CMS detectors, no hints of physics Beyond the Standard Model (BSM) emerge yet. Some tensions are seen at the intensity frontier, covered by the LHCb [3] experiment that could possibly point to BSM signals.

Since the LHC so far has collected just 5% of its total integrated luminosity (including LHC and HL-LHC), it is therefore necessary, to pursue the efforts to probe this unique very large amount of very good quality data to search for BSM signals.

In this Ph.D. project, we plan to continue the direct search for SUSY at the LHC Run 3. If SUSY exists at the TeV scale, and 1st and 2nd generation squarks and gluinos are too heavy to be detected, then top squarks and electroweak gauginos, namely charginos (C1,C2) and neutralinos (N1,N2,N3,N4) could constitute a good strategy for discovering SUSY at the LHC.

At CPPM, in the ATLAS team, we have carried successfully carried this strategy to search for charginos and neutralinos. This effort has proceeded through three Ph.D. theses:

 Run 1: Recherche de production électrofaible supersymétrique dans des cascades de désintégration contenant un boson de Higgs avec le détecteur ATLAS au LHC [4] by Michael Ughetto (2011-2014) co-tutored between University of Montpellier, J.-L. Kneur (L2C Montpellier) was the thesis director, and Aix-Marseille University where Steve Muanza and Laurent Vacavant were the co-tutors. Michael Ughetto was based at CPPM and was working most of his time under the supervision of S. Muanza, with whom Michael made important contributions to the search for the C1+N2 $\rightarrow$ W($\to$ lnu)+h($\rightarrow$ bb)+mET process where a Higgs boson was used to tag SUSY for the first time in SUSY searches at LHC. During this thesis Michael Ughetto made crucial contributions to the new C++ version of the SUSY spectrum calculator Suspect [5]. In addition M. Ughetto contributed to the continuous b-tagging under the supervision of L. Vacavant.

 Run 2 (first wave): Search for chargino and neutralino pair production in final states with one lepton, two b-jets consistent with a Higgs boson and missing transverse momentum with the ATLAS detector at the LHC Run2 [6] by Rima El Kosseifi (2015-2018). This thesis was financially supported by the OCEVU Labex [7], S. Muanza served as its director and J.-L. Kneur as the co-director. Rima and S. Muanza analyzed the 2015-2016 datasets and made important contributions for the design of the analyses (signal regions and control region for the dominant background process). Under the tutorship of J.-L. Kneur, R. El Kosseifi has developed the first bottom-up inversion trading the Higgs boson mass as a new input parameter, for parameters in the top squark sector and other soft-SUSY breaking parameters. She also contributed to study the performances of state-of-the-art b-tagging algorithms used by ATLAS for Run 2 analyses.

 Run 2 (second wave): Search for SUSY EWK production in events with isolated lepton, jets and missing transverse momentum at ?s = 13 TeV with ATLAS detector [8] by Ngoc Khanh Vu (2018-2021). S. Muanza is the thesis director and Farès Djama is the thesis co-director. N.K. Vu is participating to the first extension at LHC of the analysis to the C1+N2 $\to$ W($\to$ lnu)+Z($\to$ qq)+mET channel, under the supervision of S. Muanza, exploiting the full integrated luminosity of Run 2. Khanh is tutored by F. Djama for his work on the silicon pixel detector (current leakages in pixel and IBL, and performance of CMOS sensors for the replacement of the ITk in the second half of HL-LHC).

All of these Ph.D. theses were quite successful, the students wrote internal notes on their contributions to ATLAS b-tagging and analyses, the latter have all been published in high profile journals with peer-review. Besides, each student got a talk at an international conference or workshop where he/she had an opportunity to present results of ATLAS SUSY searches. Therefore, we're building up on this experience to lay ground for the future success of the current thesis project.

For the current Ph.D. thesis project, the research activities include a search for electroweak SUSY and, developments and study of performances of b-tagging algorithms.

 Run 3: The selected student will analyze ATLAS data to search for C1+N2$\to$ W($\to$ lnu)+h($\to$ bb)+mET and study the possibility to extend this to a production proceeding via search vector bosons fusion. Steve Muanza will tutor this part of the work.

 Preparation for Run 4: In addition to the analysis at Run 3, the student will develop the ATLAS b-tagging algorithms in view of the first part of HL-LHC, namely the Run 4 (planned to start in 2027). Starting from Run 4, the b-tagging capabilities should be extended to rapidities up to 4 in absolute value, despite the high level of pile-up (around 200 pp collisions per bunch crossing) [9]. This part of the work will be tutored by Arnaud Duperrin and Thomas Strebler, and this will constitute the qualification task of the student at the end of which he/she will earn his/her ATLAS authorship.

 Exploration in view of FCC-ee: On top of the main research activities planned in the ATLAS collaboration, the student could also explore possible contributions to the b-tagging algorithms for the IDEA detector concept for the future FCC-ee (a project at CERN for the next generation of $e^{+}e^{-}$ collider, essentially aimed at serving as a future Higgs Factory) [10].

References

[1] ATLAS Collaboration, Phys.Lett. B716 (2012) 1, arXiv:1207.7214 [hep-ex]

[2] CMS Collaboration, Phys.Lett. B716 (2012) 30, arXiv:1207.7235 [hep-ex]

[3] LHCb Collaboration, Phys.Rev.Lett. 115 (2015) 111803, Phys.Rev.Lett. 122 (2019) 1918801

[4] Thesis of Michael Ughetto, http://hal.in2p3.fr/tel-01203771v1/document, Univ. de Montpellier

[5] A. Djouadi, J.-L. Kneur, G. Moultaka, M. Ughetto, D. Zerwas, arXiv:1203.1488 [hep-ph], http://suspect.in2p3.fr/

[6] Thesis of Rima El Kosseifi, https://hal.archives-ouvertes.fr/tel-01998851/document, AMU

[7] Labex OCEVU, https://www.labex-ocevu.univ-amu.fr/

[8] Thesis of Ngoc Khanh Vu, in preparation, AMU

[9] ATLAS Collaboration, ATL-PHYS-PUB-2020-005 (2020)

[10] The Lepton Collider : Future Circular Collider Conceptual Design Report Vol. 2, Eur. Phys. J. Spec. Top. 228 (2019) 261-623

Mots clefs :
Physique des particules
Code :
Doctorat-2124-AT-02
Preparation to the Higgs self-coupling measurement using the HH -> bbyy channel.
Directeur de thèse :
Elisabeth Petit - 0033.4.91.82.72.63 - petit@cppm.in2p3.fr
Attention cette offre n'est plus disponible
Description :

Nine years after the discovery of the Higgs boson the precision measurement of its properties is a key goal of the LHC and Future Colliders in order to test the Standard Model. In particular the measurement of the Higgs self-coupling is one parameter not measured yet, that can be probed through the HH production. Even if the cross-section of the HH production is too small to be observed yet, the corresponding analyses will bring the best existing constraints on the Higgs self-coupling, in addition to setting baselines for the analyses to be performed with the dataset to be collected during the HL-LHC running.

The dataset collected up to now is expected to double during Run 3 of the LHC (2022-2024). The team has already been highly involved in the HH->bbgammagamma analysis channel. In order to discover the HH process a good understanding of the background processes is necessary, in particular the Z(->bb)H(->gammagamma) process which is an important background to the analysis and has a similar final state. We plan to measure it since it could be detected with the dataset collected during Run 3 and it is a benchmark to test the analysis strategy.

The student will work with MC simulation and real data to prepare for this measurement.

Programming skills (C++/python, ROOT) are highly recommended, as well as a background in particle physics.

Mots clefs :
Physique des particules
Code :
Doctorat-2124-AT-01
Belle II
Search for lepton flavour violating decays at Belle II
Directeur de thèse :
Justine Serrano - 04 91 82 72 80 - serrano@cppm.in2p3.fr
Description :

Being forbidden in the Standard Model (SM) of particle physics, lepton flavour 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 $b \rightarrow s\ell\ell$ and $b \rightarrow c\ell\nu$ processes, the interest of tau lepton flavor violating decays has been greatly reinforced. In particular, several new physics models predict branching fractions of $\tau \rightarrow 3 \mu$ and $\tau \rightarrow \mu \gamma$ just below the current experimental limits.

Similarly, $b \rightarrow \tau X$ decays provide powerful probes to test the presence of New Physics.

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 2030. Thanks to its clean environment and high $\tau^+ \tau^-$ cross section, it provides an ideal environment to study tau and $b \rightarrow \tau$ decays. The goal of this thesis is analyse Belle II data to provide the most stringent limit on LFV decays.

Activities:

Data analysis, participation to data taking, participation to Belle II service tasks, activities of outreach and dissemination.

Work context:

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 (if allowed by COVID crisis).

The funding of this phD is provided by an ERC grant obtained by Justine serrano.

Références:

https://arxiv.org/pdf/1806.05689.pdf

Mots clefs :
Physique des particules
Code :
Doctorat-2124-BE-01
DarkSide
Recherche directe de Matière Noire avec le détecteur DarkSide-20k / Direct search for Dark Matter with the DarkSide-20k experiment
Directeur de thèse :
Fabrice Hubaut (CPPM), Emmanuel Nezri (LAM) - hubaut@in2p3.fr , emmanuel.nezri@lam.fr
Attention cette offre n'est plus disponible
Description :

The Institute for Physics of the Universe (IPhU, Aix-Marseille University) invites applications for a PhD position in the field of Dark Matter direct searches.

Dark matter is today one of the main puzzles in fundamental physics. Indeed, its contribution to the total mass of the Universe is 85%, but it can not be explained in the framework of the Standard Model (SM) of particle physics. Several candidates exist in theories beyond the SM, and the WIMP (Weakly Interacting Massive Particle) is one of the best motivated of these candidates, as it could also solve the SM hierarchy problem (stability of the Higgs boson mass).

If the WIMP mass is O(100) GeV, its density in the Universe can be compatible with cosmological observations. Experiments searching directly for dark matter thus use our galaxy halo as a potential source of WIMPs. Since 2010, the most sensitive technology is based on the measurement of the scintillation light from the scattering of a WIMP on a liquid noble atom  argon or xenon. The DarkSide-20k experiment, which will be installed 2 km underground in the Gran Sasso laboratory in Italy, is the second generation of liquid argon detectors. It will use a cubic cryostat of 8 m side hosting a Time Projection Chamber filled with 50 tons of highly purified argon, read out by 200,000 silicon photomultipliers. This allows to have a world leading discovery potential for WIMPs. The data taking should start in 2025. The actual work is dedicated to the realization and the exploitation of a prototype, of reduced size compared to the final detector but using most technologies foreseen for DarkSide-20k. CPPM recently joined the DarkSide collaboration.

The goal of this thesis is to prepare at best WIMP searches with early DarkSide-20k data, both from experimental and phenomenological standpoints. A first axis will consist in participating to the set-up and the exploitation of the DarkSide calibration system designed at CPPM, based on radioactive sources mimicking signal and backgrounds. The student will help building and validating the system as well as defining an optimized calibration strategy for the experiment using simulation tools. In parallel, the student will improve the data reconstruction algorithms by using artificial intelligence techniques (e.g. neural networks), in order to optimize the separation between signal (nuclear recoils, NR) and background (electron recoils, ER), and fully exploit the pulse shape discrimination power between ER and NR, key element for the discovery of high mass WIMPs. This will be developed using prototype data.

These experimental activities will be complemented by a phenomenological work, whose goal is the study of uncertainties affecting the WIMP local density and velocity distribution in the Milky Way as well as the nucleon-dark matter coupling. The dark matter phase space distribution will be characterized through semi-analytical approaches (e.g halo modeling) and cosmological hydrodynamics simulations of spiral galaxies. This is a key element to improve signal predictions for DarkSide-20k, allowing more accurate interpretations of the first data.

In this framework, the student will have to do stays at CERN and Gran Sasso laboratories.

The applicants are expected to hold, or are about to obtain, the Master degree in fundamental physics. The ideal candidate will have some experience in experimental particle physics, a strong interest in instrumentation, data analysis and phenomenology, and good software skills (C++, python, ROOT). A strong motivation and an ability to work in teams and in large collaborations are highly recommended.

IPhU is a leading collaborative scientific research and education environment dedicated to the Physics of the Universe and associated technologies: from the infinitely small scales of particle physics, to the infinitely large ones of cosmology, with high-energy astrophysics in between. It brings together and synergizes the theoretical, observational and experimental skills of the three laboratories in Marseille which are internationally recognized in the field.

The PhD student will join the Centre de Physique des Particules de Marseille (CPPM) and the Laboratoire d'Astrophysique de Marseille (LAM), which are both part of IPhU. The student will work under the supervision of Fabrice Hubaut (CPPM) and Emmanuel Nezri (LAM). The position is expected to start on the 1st of October 2021 and will be funded for three years with a net salary of about 1420 euros (gross salary of about 1770 euros) per month.

The applicants should send by email to both Fabrice Hubaut (hubaut@cppm.in2p3.fr) and Emmanuel Nezri (emmanuel.nezri@lam.fr):

- a motivation letter,

- two reference letters to be sent directly to hubaut@cppm.in2p3.fr and emmanuel.nezri@lam.fr ,

- CV and university grade transcripts (for all degrees).

The deadline for submitting all the application material is the 31st of May 2021.

Mots clefs :
Physique des particules
Code :
Doctorat-2124-DS-01
KM3NeT
Multi-messenger analysis with KM3NeT
Directeur de thèse :
Damien Dornic, Vladimir Kulikovskiy - 0491827682 - dornic@cppm.in2p3.fr , Vladimir.Kulikovskiy@ge.infn.it
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 and path deviation. 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 [1] 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 parts will have a sensitivity largely improved compared to ANTARES [2] at low and high energies. The infrastructure is already deployed in both sites and the first lines have been deployed and taking data since 2019. The completion of the KM3NeT is expected to be achieved around 2025-26. Neutrino astrophysics 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 guarantees to have neutrino signal detections in KM3NeT.

The main goal of the thesis is to develop multi-messenger analyses in the two KM3NeT detectors. During this PhD implementation of the efficient all-flavour neutrino selection over the atmospheric backgrounds is foreseen. 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 PhD student will also participate to the development of the alert sending system and the multi-wavelength follow-ups (radio, visible, X-ray and VHE).

Thanks to the optical module characteristics, KM3NeT will also be able to detect the MeV neutrino signal from the future galactic supernovae. The participation to the improvement of the supernova analysis is foreseen this PhD thesis too.

The candidate should have a good background in astroparticle physics and astrophysics. The interest in the data analysis is expected together with knowledge of statistics. The analyses will be performed using C++, Python and Root on Linux platforms. This PhD will be co-directed with Vladimir Kulikovksiy from the Genova University [3] and Damien Dornic from CPPM [4]. The student is expected to pass a significant part in the other laboratory.

[1] KM3NeT: http://www.km3net.org

[2] ANTARES: https://antares.in2p3.fr/

Mots clefs :
Astroparticules
Code :
Doctorat-2124-KM-01
Measurement of $\tau$ -neutrinos with the KM3Net/ORCA neutrino telescope
Directeur de thèse :
Jürgen Brunner - 04 91 82 72 49 - brunner@cppm.in2p3.fr
Description :

Neutrinos are the most enigmatic elementary particles. They exist in three varieties, which can either be classified according to their different masses in mass eigenstates (1,2,3) or via their weak interaction channels in flavour eigenstates (e,$\mu,\tau$ ), named in accordance with their charged leptonic partners. A mixing matrix (the so-called PMNS matrix [1]) governs the transition probabilities between mass and flavour eigenstates. If the current picture of three neutrino varieties is complete, this mixing matrix must be unitary, while unitarity is violated in the presence of additional hitherto unknown neutrino species.

A new detector is being built offshore the coast of Toulon - KM3Net/ORCA [2] to explore neutrino properties in more detail. The final goal of the ORCA detector is the determination of the neutrino mass hierarchy. This will be possible with the complete detector comprising more than 100 detection lines, while other unknown neutrino properties can already be studied with the detector under construction. Currently, 6 detection lines are operational and have successfully taken data for more than one year. With these data, and those which will be taken during the thesis period 2021-2024, significant measurements of certain neutrino properties can be achieved by measuring atmospheric neutrinos in the energy range 3-100 GeV.

The goal of the thesis is to probe the unitarity of the PMNS mixing matrix. This can be achieved by measuring $\tau$ -neutrino events in the KM3NeT/ORCA detector as these are exclusively produced via neutrino oscillations. The main signature of $\tau$ -neutrinos in the detector is an excess of shower-like events. To perform such a measurement, the student has to develop a reconstruction algorithm for shower-like events and to adapt and optimize it for the existing KM3NeT/ORCA detector. A signal of up-going atmospheric neutrino showers should be isolated from the dominant background of down-going atmospheric muons. Scrutinizing the energy and angular distribution of these neutrino events should reveal a contribution of $\tau$ -neutrino events thereby addressing the question of the unitarity of the PMNS mixing matrix. The violation of unitarity would be a strong sign of physics beyond the Standard Model.

Mots clefs :
Physique des particules
Code :
Doctorat-2124-KM-02
LHCb
Test of Lepton Flavour Universality using $B \to D^*\tau\nu$ decays at LHCb
Directeur de thèse :
Olivier Leroy - 04 91 82 76 05 - Olivier.Leroy@in2p3.fr
Description :

Applications are invited for a PhD student position at the Centre de Physique des Particules de Marseille (CPPM), France. Applicants must hold a Master degree (or equivalent) in Particle Physics, or expect to obtain such a degree by September 2021. The PhD contract can start as soon as October 1st, 2021, for 3 years. The deadline for application is May 3rd, 2021, but early applications are encouraged.

LHCb is one of the four major experiments installed at the largest proton-proton collider ever built, the LHC, at Cern, Geneva, Switzerland. The experiment is dedicated to the search for Physics Beyond the Standard Model (BSM) studying beauty and charm hadrons. Since the beginning of data taking in 2010, LHCb has accumulated the largest sample of b-hadrons ever collected and published hundreds of world-leading measurements. The CPPM LHCb group is deeply involved in the experiment since its beginning.

In the past few years, two intriguing anomalies have shown up in the flavour sector. One related to the $b \to s\ell\ell$ flavour changing neutral current and another one in the $b \to c\tau\nu$ charged current. Both effects are $\sim4\sigma$ away from the Standard Model (SM) expectation.

Concerning the second effect, the measured quantities are the ratios of branching fractions $R(D(*)) = BR(B \to D^{(*)}\tau\nu) / BR(B \to D^{(*)}\ell \nu)$ , $(\ell = \mu,e)$ . In the Standard Model, the only difference between the numerator and the denominator is the lepton mass. When combining the results of the BaBar, Belle and LHCb experiments, the measurements appear to be $3.8\sigma$ away from their SM expectation. This is a striking hint of violation of the lepton flavour universality which clearly needs to be checked by all means.

The student will study the $B \to D^{(*)}\tau\nu$ channel, where the $\tau$ lepton is reconstructed into its 3 pions final state $(\pi^+\pi^-\pi^+\nu)$ . In addition to a measurement of the branching ratio, the student will perform an angular analysis of the decay products which will bring new sensitivity to BSM effects. She/he will use the full run1 and run2 data sets (2011-2018), to achieve an un-precedented precision and hopefully clarify the current situation.

The student will also participate to the commissioning of the LHCb data acquisition system for the beginning of the Run3, starting in 2022. In particular she/he will be involved in the development of the new High Level Trigger system based on GPU for the first time. The student will often travel to Cern, to participate to Run3 commissioning and data taking, and to present her/his results.

$\bf Applicant~profile:$ The ideal candidate will have some experience in experimental particle physics, a strong interest in data analysis and good software skills (C++, python, ROOT).

She/he should have excellent academic background. Applications with a detailed CV, a motivation letter and 2 recommendation letters should be sent to: Olivier.Leroy@in2p3.fr

$\bf Keywords:$ Experimental High Energy Physics, LHCb, Flavour physics, New Physics, Beyond the Standard Model searches. LFU, Lepton Flavour Universality, Flavour anomalies, Data analysis. Data Acquisition System, High Level Trigger, GPU

$\bf References:$

- Measurement of $B \to D^*\tau\nu$ branching fraction using three-prong $\tau$ decays, Phys. Rev. D97, 072013 (2018).

- Model-independent method for measuring the angular coefficients of $B \to D^*\tau\nu$ decays, JHEP 11 (2019) 133

Mots clefs :
Physique des particules
Code :
Doctorat-2124-LH-01
Renoir
Cross-correlation between CMB observables and cosmic voids in large galaxy surveys / Analyse croisée entre les observables du CMB et les vides cosmiques dans les grandes relevés de galaxies
Directeur de thèse :
Stéphanie ESCOFFIER - 04 91 82 76 64 - escoffier@cppm.in2p3.fr
Description :

Description:

The various observations of the Universe have been indicating for twenty years now that the expansion of the Universe is accelerating. The standard model of cosmology, known as the LCDM model, describes the Universe as composed of 27% dark matter and 68% dark energy. Understanding the nature of these two energy components remains one of the greatest challenges in contemporary physics. Next-generation galaxy surveys, such as Euclid or DESI, will make it possible to measure several tens of millions of galaxy spectra in the coming decade and tighten constraints on the cosmological model, or probe its alternatives like modified gravity models.

The most promising tools to constrain dark energy and gravity properties are based on the observation of large structures in the Universe. The structure of the Universe also reveals the presence of large under-dense regions, enclosed by filaments of matter. These cosmic voids, which occupy nearly 80% of the volume of the Universe, contain very few matter, and are therefore an ideal laboratory for testing dark energy scenarios.

The subject of the thesis is to extract the integrated Sachs-Wolfe (ISW) signal by cross-correlating cosmic voids with Cosmic Microwave Background (CMB). Indeed the time evolution of gravitational potentials imprints secondary anisotropies in the CMB, in addition to the primordial CMB anisotropies generated near the last scattering surface. These additional anisotropies are caused by gravitational interactions of CMB photons with the growing cosmic large-scale structure. The ISW signal is challenging to measure since it is very weak compared to primordial CMB photons. We propose here to identify cosmic voids in large spectroscopic surveys like DESI and Euclid and study how they can contribute to cold regions in the CMB temperature pattern. A focus will be given on superstructures, by stacking cosmic voids in a given direction or by identifying supervoids.

_________________________________________

Résumé:

Les différentes observations de l'Univers indiquent depuis près de vingt ans que l'expansion de l'Univers s'accélère. Le modèle standard de la cosmologie, connu sous le nom de modèle LCDM, décrit l'Univers comme étant composé de 27% de matière noire et de 68% d'énergie noire. La compréhension de la nature de ces deux composantes énergétiques reste l'un des plus grands défis de la physique contemporaine. Les sondages spectroscopiques de galaxies de la prochaine génération, tels que Euclid ou DESI, permettront de mesurer plusieurs dizaines de millions de spectres de galaxies au cours de la prochaine décennie et de resserrer les contraintes sur le modèle cosmologique, ou de sonder ses alternatives comme les modèles de gravité modifiés.

Les outils les plus prometteurs pour contraindre l'énergie sombre et les propriétés de la gravité sont basés sur l'observation de grandes structures dans l'Univers. La structure de l'Univers révèle également la présence de grandes régions sous-denses, cloisonnées par des filaments de matière. Ces vides cosmiques, qui occupent près de 80 % du volume de l'Univers, contiennent très peu de matière, et constituent donc un laboratoire idéal pour tester des scénarios d'énergie sombre.

Le sujet de la thèse consiste à extraire le signal intégré de Sachs-Wolfe (ISW) par corrélation croisée des vides cosmiques avec le fond diffus cosmologique (CMB). En effet, l'évolution temporelle des potentiels gravitationnels imprime des anisotropies secondaires dans le CMB, en plus des anisotropies primordiales du CMB générées près de la dernière surface de diffusion. Ces anisotropies supplémentaires sont causées par les interactions gravitationnelles des photons du CMB avec la structure cosmique croissante à grande échelle. Le signal ISW est difficile à mesurer car il est très faible comparé aux photons CMB primordiaux. Nous proposons ici d'identifier les vides cosmiques dans les grands relevés spectroscopiques comme DESI et Euclid et d'étudier comment ils peuvent contribuer aux régions froides identifiées dans la carte de température du CMB. L'accent sera mis sur les superstructures, en empilant les vides cosmiques dans une direction donnée ou en identifiant les supervides.

Mots clefs :
Cosmologie observationnelle
Code :
Doctorat-2124-RE-02
Preparation of the Euclid space mission: study of the correlations, at the pixel level, of the infrared detectors' response
Directeur de thèse :
Aurélia Secroun - Eric Kajfasz - 0491827215 - secroun@cppm.in2p3.fr
Description :

Euclid is an M-class ESA mission due to launch in 2022. It is one of the major observatories dedicated to cosmology and understanding the nature of Dark Energy through the mapping of all visible and infrared sky. The NISP (near-infrared spectrophotometer) instrument aboard Euclid holds the largest infrared focal plane array to fly and is filled with 16 infrared detectors specially designed and fabricated for Euclid by the American company Teledyne, and selected among 60 detectors by NASA as the highest performing detectors.

Those H2RG' detectors are constituted by a mosaic of 4 million hybrid HgCdTe pixels and make for a major contribution to the acquisition chain with a rather intricate behavior, as already observed during tests. Being able to precisely describe their behavior and extract parameters such as readout noise, conversion gain, or linearity, at the pixel level is an important challenge for reaching a sufficient processing quality and for meeting the 1% accuracy requirement on the final data.

The objective of the thesis is thus to derive a pixel' analysis of the detector response through a global approach of the various performance parameters (namely, noise, linearity, latency, etc.). This analysis will be based on the on-ground calibration of the flight detectors performed by CPPM in preparation of the Euclid mission with a view to providing reference maps at the pixel level for the correction and data processing of flight data. Two series of data are available (with some 1Po recorded on disk): a first series corresponds to the characterization of detectors carried out on dedicated test benches installed at CPPM, a second series corresponds to tests implemented during the full instrument calibration at LAM with slightly different experimental conditions.

- The pixel analysis will allow to bring out spatial variations and should lead to individual pixel performance.

- A thorough study will require looking further into the finest effects that have been revealed during the tests, and propose original methods to derive the various parameters considering their observed intertwining.

- It should also look into the correlations between pixels, the acquisition history and the experimental specificities.

The PhD student will be a member of the Euclid Consortium, with full access to Euclid data.

{\bf Keywords}: Instrumentation, Detector, Infrared, Calibration, Spectrometry, Photometry, EUCLID, Data analysis

{\bf Applicant profile}: The candidate should hold a Master of Sciences or Master of Engineering in instrumentation for space sciences or similar specialty. Good programming skills (python), good knowledge in signal processing and bases in instrumentation and semi-conductor physics are required. Strong motivation and ability to work in team are definitely appreciated.

Mots clefs :
Instrumentation
Code :
Doctorat-2124-RE-03
Constraining dark-energy and alternative models to general relativity with measurements of the growth rate of structures using galaxy surveys
Directeur de thèse :
Julian Bautista - bautista@cppm.in2p3.fr
Description :

More than twenty years after the discovery of the accelerated nature of the Universe's expansion, there is still no definitive explanation for its physical origin. Several types of dark-energy or even alternatives/extensions to general relativity have been proposed in the literature attempting to explain the acceleration of the expansion. By accurately measuring of both expansion and growth rates as a function of cosmic time, we can learn more about this cosmological mystery. Those measurements are the scientific goal of current and future experiments such as the Dark Energy Spectroscopic Instrument (DESI), the Zwicky Transient Facility (ZTF), Euclid and the Vera Rubin Observatory Legacy Survey of Space and Time (Rubin-LSST).

The Centre de Physique de Particules de Marseille (CPPM) is offering two doctoral positions starting in October 2021 for a duration of three years in the topic of observational cosmology. The goal is to measure the growth-rate of structures using galaxies from DESI or Euclid, eventually combining them with direct peculiar velocities estimates from ZTF or Rubin-LSST type-Ia supernovae. The PhD projects will include extensive work on data analysis, both simulated and observed, development of models and estimators, and the use of high-performance computing centres across the globe. Experience with cosmology, scientific computing (e.g. python), statistics and data analysis is highly recommended.

The Centre de Physique de Particules de Marseille (CPPM)~is~a multi-disciplinary CNRS~laboratory~hosted~by~the Aix-Marseille Université~with~top~researchers~in the~domains~of~particle~physics, neutrinos,~astroparticles, and~cosmology.~The CPPM~participates in the construction and scientific exploitation of the main~ongoing~and future~cosmological~projects~such~as the~Dark~Energy~Spectroscopic~Instrument (DESI), the Zwicky Transient Facility (ZTF), Euclid and the Vera Rubin~Observatory~Legacy~Survey of~Space~and Time (Rubin-LSST). The~cosmology~group~is a dynamic team composed of PhD students, postdocs, engineers and researchers~experts in the clustering of galaxies,~cosmic~voids, type-Ia~supernovae. The CPPM is a close partner of the Laboratoire d'Astrophysique de Marseille and the Centre de Physique Théorique, both in the Marseille area.

The candidates should send to bautista@cppm.in2p3.fr the following items :

- a CV

- a one-page statement of their motivations

- the latest academic transcript of records available

- one recommendation letter to be sent directly to bautista@cppm.in2p3.fr by the recommender

Application deadline: 11 July 2021

Included Benefits: French national medical/dental insurance, maternity/paternity leave, lunch subsidies, family supplement for children, participation to public transport fees, pension contributions. School is free in France for all children above 3. French lessons are also offered by the institution.

Inquiries about the job: Julian Bautista, bautista@cppm.in2p3.fr

Mots clefs :
Cosmologie observationnelle
Code :
Doctorat-2124-RE-05
Constraining dark energy parameters or probing new cosmology with supernova dataset
Directeur de thèse :
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 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].

During this PhD, we propose to prepare the first analysis of LSST supernova data. The PhD candidate will start preparing the analysis using the LSST software and our deep learning method for identifying supernova on existing HSC/Subaru data. Indeed, the HSC data has characteristics that are very close to what we expect with Rubin/LSST. Once the methods are well validated on HSC data, the PhD candidate will participate to the preparation of the key SN analysis of Rubin LSST/DESC with emphasis on mitigate and evaluate the systematical errors from type identification and calibration.

Mots clefs :
Cosmologie observationnelle
Code :
Doctorat-2124-RE-04
Constraints on gravity by tomographic galaxy clustering with Euclid data
Directeur de thèse :
GILLARD William - Escoffier Stephanie - 0491827667 - gillard@cppmin2p3.fr
Attention cette offre n'est plus disponible
Description :

The various observations of the Universe have been indicating for twenty years now that the

expansion of the Universe is accelerating. The standard model of cosmology, known as the

CDM model, describes the Universe as composed of 27% dark matter and 68% dark energy.

Understanding the nature of these two energy components remains one of the greatest

challenges in contemporary physics.

The future Euclid space mission is dedicated to the study of dark energy and dark matter in

the Universe and to test gravity on cosmological scales. Euclid was selected by the European

Space Agency (ESA) in 2011 and will be launched in 2022 to probe the Universe over a 6 yearperiod.

These data will revolutionize our ability to map the Universe and better understand

the nature of dark energy or put Einstein's General Relativity (GR) in default.

Two instruments will be embarked on board Euclid, the Near Infrared Spectrometer and

Photometer (NISP) and the visible imager (VIS). The spectroscopic survey with the NISP

instrument will target fifty millions of galaxies in the redshift range 0.9 < z < 1.8. The

photometric survey will get the image and photometric redshift of two billions of galaxies

down to a magnitude of 24.5 AB covering the redshift range 0 < z < 2.5.

The subject of the thesis is to measure the galaxy clustering from the Euclid photometric

catalog using a tomographic approach. The tomographic approach (2D) has several

advantages compared to the standard 3D mapping. On the one hand, the number of observed

objects is two orders of magnitude larger, since 2 billion galaxies are expected in imaging

compared to the 50 million galaxies expected in spectroscopy. The division into several tens

of slices in redshift makes it possible to keep a competitive statistic in each slice. On the other

hand, the angular approach does not require fiducial cosmology for the conversion of

distances, which makes it possible to constrain the cosmological models as cleanly as possible.

The interest of applying this method to Euclid data is to take advantage of the double

photometric/spectroscopic observation on the same fields to calibrate the photo-z.

The first step of the thesis work will consist in calibrating the photometric redshifts (photo-z)

of Euclid from the spectroscopic sample. This step will be done first from the Euclid Flagship

simulation which contains more than 3 million objects. A machine learning approach will be

considered. Then the angular clustering tools will be developed in order to extract the

clustering signal from the photometric samples. This analysis will require the optimization of

the processing chain in order to be able to process more than a thousand mocks for the

calculation of covariance matrices. The PhD student will be member of the Euclid Consortium,

Keywords :

Cosmology, Dark Energy, Dark Matter, General Relativity, Galaxy Clusturing, BAO, Data Analyses, Tomograpgy, Big Data, Deep Learning, EUCLID, NISP, Photometry, Spectroscopy

Applicant profile :

Master in fundamental physics or astrophysics. Interest for cosmology and machine learning

tools. Programming skills (python, C++), strong motivation, ability to work in teams and in

large collaborations are highly recommanded.

Mots clefs :
Cosmologie observationnelle
Code :
Doctorat-2124-RE-01