Post doc in instrumentation and acceleator physics

Post doc in instrumentation and acceleator physics

Super

KEKB is currently the highest-performance e⁺e⁻ collider in operation. It has achieved a world-record luminosity, delivered to the Belle II particle physics experiment. This experiment focuses particularly on the decays of B and D mesons with high precision, as well as the production and decay of tau leptons. The latter are produced in such large quantities that precision studies can be carried out at Belle II.

To date, the colliding beams are not polarized. This limitation could be overcome around 2030 with an upgrade of the collider, which would enable the storage of polarized electrons. As a result, the data collected by Belle II could be used to perform precision measurements of electroweak quantities such as the weak mixing angle or the anomalous magnetic moment of the tau [1].

To successfully achieve this ambitious upgrade of the accelerator, it is necessary (i) to modify the electron source so that it produces polarized electron beams; (ii) to ensure their proper transport to the Super

KEKB collision ring and the preservation of a sufficient level of polarization; (iii) to be able to manipulate the spin orientation of the electrons in the collider; and (iv) to have real-time diagnostics of the polarization in the accelerator. This last aspect lies at the core of IJCLab’s contribution to the project and of the ANR COMPO. This diagnostic system consists of a Compton polarimeter.

Photons from a laser are back scattered off the electrons in the accelerator. The energy of these scattered photons is then measured, providing precise information on the degree of longitudinal polarization of the electron beam. Preliminary studies have been conducted, demonstrating the feasibility of the project [2].

The proposed fixed-term researcher position focuses on developing and testing a calorimeter capable of measuring the energy of photons scattered via the aforementioned Compton interaction with sufficient precision. This detector must (i) be fast, since one aims to distinguish photons scattered from two electron bunches separated by four ns; (ii) be radiation-tolerant, since it will be exposed to a significant integrated dose linked to the photon signal to be measured;

and (iii) rely on a data acquisition system operating synchronously with the accelerator to identify the bunches and allow rapid polarization analysis, ultimately enabling real-time feedback to the control room.

During this work, a prototype detector consisting of a scintillator, a photomultiplier tube, and readout electronics will be developed with support from engineers and scientists of the engineering and accelerator divisions. The work will involve extensive experimental developments in the test area, complemented by GEANT4 simulations, which will then be used to estimate the performance of the polarimeter that will be implemented on Super

KEKB. The recruited researcher will be responsible for these experimental developments jointly with a PhD-contract recruit. The fixed-term researcher will focus particularly on the development of the data acquisition (DAQ) chain and will contribute to all experimental developments. They will also have the opportunity to participate in data-taking campaigns scheduled for 2026 and 2027 se campaigns aim to demonstrate that polarized beams can be preserved for a sufficiently long time in the Super

KEKB collision ring. Weekly (or more frequent, as necessary) meetings will be held to monitor progress and address any issues that arise.

A 3-years position is funded by the ANR project COMPO.

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