Description of the thesis topic

During the 3-year doctoral position, the successful candidate will work on the very high-precision measurement of photon polarization in b -> s gamma transitions. More precisely, she/he will work on angular analyses using recent Run3 data registered with the new LHCb Upgrade-I detector. Indeed in 2024, LHCb has recorded more data than during the period 2011-2018 and the amount of data which should be recorded in 2025 is expected to be even higher. She/he will also monitor the performances of the calorimeter and more generally of the electron reconstruction in the context of the LHCb Upgrade-I. She/he will work in collaboration with LHCb-IJCLab members and with our collaborators in LHCb. On top of the PhD thesis writing, the successful candidate will publish her/his results on data analyses and will present them in conferences.
The measurement of the photon polarization in b tp s gamma transitions can be very precisely performed via the study of the angular distributions of the B to K*e+e- and Bs to Phi e+e- decays. Therefore, the analyses will focus on the very low di-electrons invariant mass kinematical region where the e+e- pair comes predominantly from a virtual photon. With this measurement one can access the rate of right-handed photons in b -> s gamma transitions and search for BSM signs since, in the Standard Model, the photon is left-handed in those decays.
The main activities will be :
o to revisit the selections for the B to K*e+e- and Bs to Phi e+e- decay modes given the upgraded LHCb detector, the larger size of the data sample and the more challenging environment due to higher pile-up.
o To characterise the backgrounds and to design the optimal way to extract the physical parameters of interest in order to confront them to the SM predictions.
o To monitor of the performances for the electron reconstruction in Run3 with the increased pile-up and potential ageing of the calorimeter.

Work Context

IJCLab is a CNRS/IN2P3, Université Paris-Saclay and Université de Paris, laboratory located at the campus of the University Paris- Sud at Orsay. The campus is conveniently located 20 km south of Paris and is easily reachable by regional train 40 mins) . IJCLab is the largest CNRS laboratory in fundamental research whose main field is the “physics of the two infinities”. It gathers around 740 people with research topics spanning from the study of the elementary particles to cosmology. The largest department is the High Energy Physics one where 100 researchers (including about 30 doctoral students) are working.
The doctoral position is part of the Chiaroscuro project corresponding to a 5-year ERC grant which has started on October 2021 on the study of b to q ll transitions during Upgrade-I. It has been extended up to the end of 2028. The successful candidate will be part of the LHCb IJCLab team (~a dozen of researchers) which is included in the High Energy physics Department of IJCLab. The doctoral student will also have the opportunity to interact with the active Flavour physics phenomenology group of IJCLab. 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.
Skills required:
Education: master in experimental particle physics.
• Physics: some knowledge in flavour physics is preferred though not mandatory.
• Programming: knowledge in python or C++, and ROOT.
• Language: Fluency in spoken and written English. Some level of French could be useful.
• Good communication skills and ability to work in a team.

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.

Constraints and risks

The successful candidate will be enrolled on the PhD program of the PHENIICS doctoral school. She/he will regularly go to CERN to participate in the data taking of the LHCb experiment, taking part in shifts and ensuring data qualiy and to attend physics meetings.

Additional Information

Skills required:
Education: master in experimental particle physics.
• Physics: some knowledge in flavour physics is preferred though not mandatory.
• Programming: knowledge in python or C++, and ROOT.
• Language: Fluency in spoken and written English. Some level of French could be useful.
• Good communication skills and ability to work in a team.