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Portal > Offres > Offre UMR5814-CLABOM-016 - Chercheur sur LHCb "étude de la violation de CP dans le système des mésons Bs" (H/F)

Postdoctoral position to work on physics analysis and calorimeter calibration tools in LHCb experim

This offer is available in the following languages:
Français - Anglais

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General information

Reference : UMR5814-CLABOM-016
Date of publication : Tuesday, March 26, 2019
Type of Contract : FTC Scientist
Contract Period : 24 months
Expected date of employment : 1 September 2019
Proportion of work : Full time
Remuneration : Between 2530,09 and 3509,82 € monthly gross, according to work experience.
Desired level of education : PhD
Experience required : 1 to 4 years


The LHCb group of LAPP is inviting applications for a postdoctoral position to work on physics analysis and
calorimeter calibration tools. The group has a long‐standing expertise in flavour physics and calorimetry and is currently engaging in an additional measurement of the CKM phase φs using Bs decays to J/ψ η(η'). This phase is
responsible for CP violation in interference between direct decay and decay after mixing in the Bs system. It
provides a sensitive probe for physics beyond the standard model thanks to its precise predicted value. The
above‐mentioned decays are complementary to the golden mode Bs → J/ψ φ for the measurement of φs. They
will become increasingly interesting with the larger data set to be collected at higher luminosity during the Run
III of LHC, for which several aspects of the calorimeter reconstruction and calibration will need to be revisited.


The successful candidate will participate in the analysis of Bs → J/ψ η(η') decays and in calorimeter-related developments for the running of LHCb at higher luminosity.

To maximise the number of Bs mesons, the main decay modes of the pseudo-scalars are considered: η → γγ, π+π-π0, π+π- γ and η' → ργ, π+π-η. The respective signal samples will eventually be combined for a time-dependent asymmetry measurement. In a first step, branching ratios and lifetime will be measured in the various modes using the full Run I (2011-2012) and Run II (2015-2018) LHCb data set. The successful applicant is expected to refine the selections and fit models for each mode.

Systematic effects related to calorimeter objects will be addressed by means of photon calibration samples accessible through a dedicated software interface which will be improved and delivered to the collaboration. An improved reconstruction of the photon energy will also be investigated to reduce fluctuations due to pile-up and calorimeter aging. This will be useful for the LHCb data taken during Run II in particular, but also to prepare for future running at higher luminosity.

As a preparation for Run III (2021-2023), the candidate will study the expected precision to φs with larger data samples, based on Monte Carlo toy studies and on the performance achieved so far. He/she could also take part in making the online ECAL calibration to function at increased pile-up, and in adapting the selections of trigger lines used for neutral PID calibration.

On both fronts (physics analysis and calorimeter performance), the candidate will be expected to explore the possibilities offered by present Deep Learning techniques.


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

Work Context

LAPP is a combined CNRS and Université de Savoie Mont-Blanc unit. Close to 150 people are working at LAPP: researchers, professors, engineers and support staff, students and visiting scientists. The laboratory is very actively involved in several large international collaborations working on accelerators (ATLAS and LHCb on the LHC at CERN, BaBar at SLAC in California, OPERA in Gran Sasso) and astroparticle experiments (Virgo, AMS, H.E.S.S. and CTA). Involved in many R&D and construction programs for large research infrastructures, the laboratory's skills cover a large scope of domains involving innovative technologies in micro-electronics, complex mechanical structure design and optimization, grid computing and scientific software developments. 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 for scientists contributing to particle and astroparticle physics. LAPP hosts the MUST mid-range data storage and computing centre - widely open to distributed computing infrastructure supporting research and academic projects.

LHCb is one of the four main experiments at LHC (with ATLAS, CMS and ALICE) and is dedicated to the study of heavy flavour physics which is essential to the indirect search for physics beyond the standard model by means of precision measurement of CP violation in beauty and charm hadrons. The LAPP group has a long-standing expertise in flavour physics and calorimetry since the beginning of the data taking of the experiment. It contributed significantly to the migration of the calorimeters calibration to the online trigger system for the start of data taking in 2015. Several members had convenership responsibility in the calorimeter objects and particle identification working group. The group also published several studies on the Dalitz plot analysis of open-charm decays as well as on quarkonia spectroscopy. Finally, the group takes a leading role in the development of firmware and of the novel 40 MHz data acquisition system for the upcoming LHCb upgrade.

Constraints and risks

Some short trips have to be planned in France and abroad

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