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CMS ECAL Laser Monitoring system upgrade for LHC Phase 2 and ECAL timing calibration H/F

Vacancy details

General information


The French Alternative Energies and Atomic Energy Commission (CEA) is a key player in research, development and innovation in four main areas :
• defence and security,
• nuclear energy (fission and fusion),
• technological research for industry,
• fundamental research in the physical sciences and life sciences.

Drawing on its widely acknowledged expertise, and thanks to its 16000 technicians, engineers, researchers and staff, the CEA actively participates in collaborative projects with a large number of academic and industrial partners.

The CEA is established in ten centers spread throughout France



Position description


Intrumentation, metrology and control



Job title

CMS ECAL Laser Monitoring system upgrade for LHC Phase 2 and ECAL timing calibration H/F

Socio-professional category


Contract duration (months)

24 to 36 months

Job description

The ECAL LM system is designed to measure in quasi-real time the crystal transparency losses due to irradiation and their recovery, in order to correct the variation of the ECAL response versus time and preserve the excellent intrinsic energy resolution of the ECAL. This measurement is performed by sending laser light, during abort gaps, through the ECAL crystals read by their photodetectors and to reference PN diodes, in order to infer a transparency correction from the response ratio with a precision at the per mil level. For phase 2, a new charge pre-amplifier ASIC was developed in Saclay (MONACAL), together with new modules (called HL-MEM) to read the generated signals and integrate them in the DAQ system. Several tasks will have to be conducted in parallel by the successful candidate to integrate the new developments for the LM at phase 2:
1.     The first task will be the definition of the integration of these new LM components in the existing ECAL super-modules (SM) and LM system. The installation procedure will have to be defined on the spare SM “SM36” (SM36 will be used also to test the integration and performance of other developments like CATIA for example with the upcoming November 2022 test-beam at CERN). This work should take a few months only and will require to interact with the ECAL technical coordination, the ETH group for the installation, and the various actors in Saclay, including the group involved in mechanics and cooling studies. The candidate will acquire a deep knowledge of the ECAL and its LM system as well as the ECAL community, with several trips at CERN.
2.     The second task is the definition of the new LM data acquisition. The full data acquisition chain will have to be revisited for phase 2: from the data format to the laser monitoring software. This will require software development on one side, and interacting with people responsible of the firmware to define the needs on the other side. Interacting with many groups will thus again be needed, including with the DAQ group at CERN, but also the HLT and the Tier0.
3.   The third task will be the definition of the procedure to (inter-)calibrate the ECAL timing with LM data and its automatization. For phase 2, the timing resolution will be significantly improved (from about 120 ps currently to less than 50 ps) and the timing information from ECAL and from other sub-detectors will allow to reduce the impact of increased PU drastically. The laser data will be used to monitor the timing in the ECAL and to intercalibrate channels. This timing calibration will have to take into account the transparency losses and pulse shape changes. The spare SM36 could be used to take laser data to validate the procedure, once defined, and assess its precision.
The candidate will thus have a very wide variety of activities and interact with many people from different areas: mechanics, integration and technical coordination, DAQ, calibration…

Applicant Profile

The Department of Particle Physics at the CEA-Saclay/IRFU is currently
seeking a talented and highly qualified postdoctoral researcher to work
in the CMS experiment with a two years contract, renewable for one year.

The successful candidate will join the CMS group of the Department which
effort is focused on, but not limited to, the exploration of the scalar
sector of the Standard Model via the study of Higgs boson decays in the
diphoton channel. The CMS-Saclay group is also strongly involved in the electromagnetic calorimeter (ECAL) operation, calibration and upgrades, with several major responsibilities over the past years. Regarding the ECAL barrel phase 2 upgrades, the group is leading the design of the new front-end readout ASIC “CATIA” and the upgrade of the LM system.

The contract is expected to start in 2022. The successful candidate will be based at CEA-Saclay with opportunities to visit CERN regularly. Interested candidates should send a CV, a brief motivation letter (one page) and two recommendation letters to the following address:

Position location



Job location

France, Ile-de-France, Essonne (91)


cea saclay

Candidate criteria

Recommended training

PhD thesis in particle physics or instrumentation for particle physics


Position start date