PhD position in Accelerator Physics : Development of a fast calorimeter for real time Compton polarimetry of SuperKEKB electron beams. (M/F)

Role: PhD position in Accelerator Physics : Development of a fast calorimeter for real time Compton polarimetry of SuperKEKB electron beams. (M/F)
Organization: CNRS - National Center for Scientific Research, Laboratoire de physique des 2 infinis - Irène Joliot-Curie (IJCLab)
Location: Orsay, France
Contract Type: Temporary, Full-time (35 hours/week)
Start Date: 1 Oct 2026
Application Deadline: 26 Jun 2026 - 23:59 (UTC)

Role Overview:
The Irène Joliot-Curie Laboratory of the Physics of the Two Infinities (IJCLab) is a laboratory for the physics of the two infinities, under the supervision of CNRS, Université Paris-Saclay, and Université de Paris. The laboratory's research themes include nuclear physics, high-energy physics, astroparticles and cosmology, theoretical physics, accelerators and particle detectors, as well as technical research and development and associated applications for energy, health, and the environment. The structure has significant technical capabilities (around 280 engineers and technicians) in all major areas required to design, develop, and implement the experimental devices necessary for its scientific activity: mechanics, electronics, computing, instrumentation, acceleration techniques, and biology techniques. These technical strengths represent a major asset for the design, development, and use of the necessary instruments (accelerators and detectors). The presence of research infrastructures and technological platforms gathered on the laboratory site is also a major asset. Finally, around 90 administrative and support staff work alongside scientists and engineers.

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.

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].

Responsibilities:
The PhD student 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.

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 doctoral contract recruit. The fixed-term researcher will particularly focus on developing the electronic acquisition chain (DAQ) and will contribute to all experimental developments. They will also have the opportunity to contribute to data collection scheduled for 2026 and 2027 at KEK and their analysis. These aim 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.

Requirements and Qualifications:
- Education: Master's degree in instrumentation or subatomic physics.
- Experience: 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.
- Languages: Excellent written and spoken English is required; knowledge of French is a plus but not necessary.
- Personal Attributes: Curious individual capable of tackling a variety of physics questions at the interface of particle physics and detectors. Interested in experimental developments, detectors, and electronics, as well as simulation studies. Must be autonomous in daily work. Must be able to work with remote collaborators, process numerous sets of simulated data, and report work concisely.

Application Requirements:
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.

References:
[1] A. Accardi et al., arXiv:2205.12847
[2] D. Charlet et al., 2023 JINST 18 P10014