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Home page > PhD fellowships > Proposed PhD subjects 2016-2019 > ATLAS : Development and Performance of a Pixel detector for ATLAS at the HL-LHC

ATLAS : Development and Performance of a Pixel detector for ATLAS at the HL-LHC

by Luc Frappat - 17 December 2015

Topics:  LHC Physics, Instrumentation, ATLAS collaboration

Proponents:  Jessica Lévêque, Rémi Lafaye, Stéphane Jézéquel

Address: LAPP - 9, chemin de Bellevue - BP 110 - 74941 ANNECY-LE-VIEUX CEDEX

Phone:   +33 (0)450 09 16 32 (J. Levêque), + 33 (0)450 09 16 52 (R. Lafaye), + 33 (0)450 09 16 26 (S. Jézéquel)

Contact Email:,,

Project overview :
On the 4th July 2012, the ATLAS and CMS collaborations reported the discovery of a new boson, very similar to the long-sought Higgs boson introduced more than 50 years ago in the Standard Model (SM) of particle physics. With the full data set collected during the LHC run I (25 fb-1), both collaborations were able to measure most of the properties of the new particle (spin, parity, couplings to bosons and fermions), which were found to be in agreement with the SM predictions within the experimental precision. A further extension of the LHC program, the High-Luminosity LHC (HL-LHC) Phase II starting in 2025, is aimed at delivering 3000 fb-1 at sqrt(s) =14 TeV. This huge dataset will allow to reach a few percent precision on the Higgs boson couplings measurements, to provide a first measurement of its self-coupling -a key element to probe the EWSB mechanism- and to explore a large phase space beyond the Standard Model.
To preserve the detector performance during HL-LHC Phase II, the Inner Tracker of the ATLAS detector will have to be fully replaced. To keep the same tagging and reconstruction efficiency in a high pile-up environment, the tracker granularity and the readout rates will have to be significantly improved compared to the current ATLAS detector.
An innovative design using inclined sensors, the "Alpine Layout" initiated by the ATLAS-LAPP team, is a possible option for the pixel detector layout. This geometry has the advantage of reducing the pixel area (hence the detector cost) by almost a factor of two compared to a classical layout, while addressing several mechanical issues, such as the reduction of inactive material and an easier installation and maintenance. To be chosen as one of the baselines for the ATLAS Inner Tracker Design Report (TDR) in 2017, this layout has to demonstrate its feasibility and performance within the coming years.
The PhD student will participate in the R&D activities at LAPP, in close collaboration with the engineers, technicians and physicists. In view of the TDR in 2017, the first part of the PhD will focus on the building and qualification of fully equipped alpine staves (test beam, test bench). The second part will address the qualification of the layouts chosen for the TDR. In addition, simulations within the ATLAS detailed simulation framework will be carried out to demonstrate the physics performance of the Alpine Pixel Layout in the HL-LHC environment, and compared to the test beam results. A particular emphasis will be put on the b-tagging performance in conjunction with Run-2 collision data analysis of two photons plus two b-jets events in preparation for the Higgs self-coupling measurement. Regular trips to CERN are expected, and the possibility for a few months stay at CERN can be considered.