M2: Search for new phenomena through the study of vector-bosons polarization at LHC with the ATLAS experiment (M/F)

Job Description

Missions

Context:
The proposed internship and PhD subject uses the polarization states of gauge bosons pairs (W and Z) produced by scattering in proton–proton interactions at the LHC at energies of 13 to 13.6 TeV as probes ito look for signs of new physics. This search is one of the major goals of the LHC, following the observation of the Higgs boson in 2012.
The Higgs mechanism is an essential ingredient of the Standard Model that ensures the calculated crosssection for gauge-boson scattering does not diverge at high energies, i.e. in the regime where new particles or interactions are expected. Validating these calculations through the experimental study of polarized vector-boson scattering (VBS) is therefore complementary to measurements based on the direct detection of the Higgs boson. In particular, the scattering of longitudinally polarized gauge bosons is closely linked to the Higgs mechanism. These processes are, however, among the rarest ever measured at the LHC, and their study is still in its infancy. It could reveal signs of new physics. Thus, very recently, thanks to the work of the LAPP team, a major milestone was reached with a first measurement of the longitudinal polarization states of scattered W and Z bosons [1], based on a partial data sample.

Summary of the internship work:
The proposed M2 internship follows directly from this result and will make use of all the LHC Run 3 data available at the time: for the first time, the candidate will have access to the complete dataset collected by the ATLAS experiment from 2015 to 2026, i.e. an unprecedented integrated luminosity of 450 fb⁻¹.

The planned work will focus on improving the techniques used to separate the longitudinal and
transverse polarization states of the bosons, by exploiting novel artificial intelligence (AI) methods. The primary goal will be to check, with more data, whether the small yield of longitudinally polarized W bosons measured in the previous result corresponds to a statistical fluctuation or is confirmed. Its confirmation could be a sign of new physics.
The candidate's work will be integrated into the analysis group of the international ATLAS collaboration working on this WZ final state, a group coordinated by the LAPP team. This will ease the student's onboarding into the analysis and enhance the visibility of his work. The student may also interact with theorists.

Possible opening towards a PhD subject:
The internship may be extended into a PhD thesis whose main goal will be to carry out the measurement of the polarization states of the vector bosons produced in WZ scattering, exploiting the full ATLAS dataset at 13 and 13.6 TeV. This will require the development and use of advanced AI algorithms, aimed at increasing the sensitivity of the analysis to the extremely rare signal events being searched for. The measurements will then be compared with Standard Model predictions to search for possible signs of new physics. The results will be published in a peer-reviewed international journal.
These developments will also build on phenomenological work carried out in collaboration with theorists at the international level; the LAPP group already has close connections with the theoretical experts in this field.
Furthermore, the proposed study will constitute an excellent preparation for the analyses of the High-Luminosity LHC (HL-LHC) phase, planned after the ongoing long shutdown. Indeed, the measurement of polarized vector-boson scattering is one of the two major goals of the HL-LHC phase, alongside the study of the Higgs boson self-coupling. The subject is therefore highly promising.
Within the ATLAS collaboration, the student will also be involved in more technical developments. At the candidate's choice, this may take the form of contributions to the group's hardware projects, which will then be in the deployment phase at CERN for the start of the HL-LHC. Work related to the understanding of detector responses and performance, such as lepton detection, or jet reconstruction and identification of their substructure, as part of the improvement of algorithms for the HL-LHC, may also be considered.
The geographical proximity of LAPP to CERN will facilitate the student's direct involvement in the life of the experiment, with participation in collaboration meetings as well as in the preparations for the HL-LHC start-up in 2030.
Finally, the candidate's work will be an integral part of the European network COMETA, which brings together members of the ATLAS experiment as well as members of the CMS experiment and theorists, thus offering the candidate even greater potential visibility for their work.

Your Profil

Skills:
Currently pursuing a Master's degree (MASTER 2).

Technical Skills:
Ability to present work in English (B2 level).

Personal Skills:
Passion for research and experimental physics.
Ability to work as part of a team.

Your Work Environment

Description of the employer

LAPP is a laboratory of the Institute of Nuclear Physics and Particle Physics (IN2P3), an institute of the National Center for Scientific Research (CNRS), which coordinates programs in these fields. LAPP is a joint research unit (UMR 5814) of the CNRS and the University of Savoie Mont-Blanc (USMB). More than 150 researchers, teacherresearchers, engineers, technicians, administrators, students, and foreign visitors work there. The research carried out at LAPP aims to study the physics of elementary particles and their fundamental interactions, as well as to explore
their links with the great structures of the Universe. The work of the LAPP teams aims, among other things, to understand the origin of the mass of particles, to unravel the mystery of dark matter or to determine what happened to
the antimatter present in our universe at the time of the Big Bang. The location of LAPP, 50 km from CERN, and the presence of the theory laboratory LAPTh in the same premises, make the LAPP campus a very attractive research
place. LAPP hosts the MUST mid-range data storage and computing center.

Special conditions of exercise

Short-term travel is expected both in France and abroad.

Compensation and benefits

Compensation

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

The research professions