Missions

SuperKEKB is currently the most powerful e+e- collider. It has achieved a world record in luminosity, delivered to the Belle II particle physics experiment. This experiment precisely studies the decays of B and D mesons, as well as the production and decays of tau leptons. The latter are produced in such quantities that precision studies can be conducted at Belle II. To date, the colliding beams are not polarized. This limitation is expected to be overcome by 2030, during an upgrade of the collider to store polarized electrons. Thus, the data collected by Belle II can be used to perform precision measurements of electroweak quantities such as the electroweak mixing angle, or measurements of the tau lepton's anomalous magnetic moment [1].
To successfully carry out this ambitious accelerator upgrade, it is necessary to: (i) modify the accelerator's electron source so that it produces polarized electron beams; (ii) ensure their proper transport to the SuperKEKB collision ring and maintain a sufficient level of polarization; (iii) be able to manipulate the spin orientation of electrons in the collider; (iv) have real-time diagnostics of polarization in the accelerator.
This last aspect is at the heart of IJCLab's contribution to this project and the ANR COMPO. This diagnostic consists of a Compton polarimeter. Photons from a laser are backscattered off the accelerator's electrons. The energy of these scattered photons is then measured, allowing precise information to be extracted about the degree of longitudinal polarization of the electron beam. Preliminary studies have been conducted, concluding the feasibility of the project [2].
The fixed-term researcher will focus on developing and testing a calorimeter for the sufficiently precise measurement of the energy of photons scattered by the aforementioned Compton interaction. This detector must be: (i) fast, as we want to distinguish photons scattered by two electron bunches separated by 4 ns; (ii) radiation-tolerant, as it will be subject to a significant integrated dose related to the photon signal we wish to measure; (iii) equipped with acquisition operating synchronously with the accelerator to identify bunches and enable rapid polarization analysis, with the aim of transmitting this information in real time to the control room. The fixed-term researcher will work under supervision of the ANR COMPO PI, Aurélien MARTENS in the ILE group of Accelerator pole and in close collaboration with members of the Detectors and related instrumentation department of the engineering pole of IJCLab.
References: [1] A. Accardi et al., arXiv:2205.12847 [2] D. Charlet et al., 2023 JINST 18 P10014

Activités

During this work, a detector prototype comprising a scintillator, photomultiplier, and acquisition electronics will be developed with the support of engineers and scientists from the engineering and accelerator departments. This will involve numerous experimental developments in a test room, supplemented by GEANT4 simulations, which will then be used to estimate the performance of the polarimeter to be implemented on SuperKEKB. The recruited individual will be responsible for these experimental developments, in conjunction with a PhD candidate. The post-doctoral fellowship will thus have the opportunity to contribute to PhD candidate training and gain experience in training younger researchers. The fixed-term researcher will particularly focus on developing the electronic acquisition chain (DAQ) and will contribute to all experimental developments. She/he will also have the opportunity to contribute to data collection scheduled for 2026 and 2027 at KEK and their analysis. Indeed, during this data taking period the aim is to demonstrate that polarized beams can be preserved for a sufficiently long time in the SuperKEKB collision ring. Weekly meetings (or more frequent if necessary) will be organized to monitor and resolve encountered difficulties.

Compétences

The candidate must hold a PhD in instrumentation or subatomic physics, with a willingness to work on instrumental developments. Knowledge of detector physics, accelerator physics, and/or particle physics is a plus. Expertise in instrumentation is interesting but not critical for the envisioned work. Programming experience is also beneficial. Excellent written and spoken English is required; knowledge of French is a plus but not necessary. We are looking for a curious individual capable of tackling a variety of physics questions at the interface of particle physics and detectors. They must be interested in experimental developments, detectors, and electronics, as well as simulation studies. The recruited individual will work with remote collaborators, process numerous sets of simulated data, and be required to report their work concisely. They must also be autonomous in their daily work.

Contexte de travail

The Irène Joliot-Curie Physics Laboratory of 2 Infinities (IJCLab) is a UMR under the supervision of the CNRS (IN2P3), the University of Paris-Saclay and the University of Paris is located on the campus of the University of Paris -Saclay in Orsay. The laboratory is located on the campus of the Université Paris-Sud, Université Paris-Saclay in Orsay. The campus is located 20 km south of Paris and easily accessible by RER in 35 minutes.
IJCLab was born in 2020 from the merger of five units (CSNSM, IMNC, IPN, LAL, LPT). The staff is made up of nearly 560 permanent (340 engineers, technicians and administrators and 220 researchers and teacher-researchers) and approximately 200 non-permanent including 120 doctoral students. The research themes of the laboratory are nuclear physics, high energy physics, theoretical physics, astroparticles, astrophysics and cosmology, particle accelerators, energy and the environment and health. IJCLab has very significant technical capacities (around 280 IT) in all the major fields required to design, develop / implement the experimental devices necessary for its scientific activity, as well as the design, development and use of instruments. .
The researcher will work within the ILE group (4 faculty researchers, 3 CNRS researchers, 2 PhD students) of the accelerator physics department, which has developed expertise over more than twenty years in Compton interaction for the production of high-energy photons—ranging from tens of keV for medical and imaging applications, to a few MeV for nuclear physics, and several GeV for electron beam diagnostics for particle physics colliders. A significant part of the activities focuses on designing systems for precise diagnostics of electron beam polarization. The proposed work will thus fully align with the group's scientific objectives.
IJCLAB bases its recruitment policy on the promotion of equality, diversity and inclusion. Essential values, they allow the professional development of agents, who are real actors in a collective success, but also the development of the laboratory itself.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

Meetings and validation tests are planned at KEK, Tsukuba, Japan, for durations of one to six weeks (depending on needs). Contributions (posters, oral presentations) at conferences are expected based on the results obtained. The use of radioactive sources and accelerator tests are planned. The recruited individual will therefore be subject to radiological risk.

Informations complémentaires

Applications must include a detailed CV with no date gaps, showing degrees, at least two references (people who can be contacted), and a one-page motivation letter.