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ATLAS with a taste of Savoy

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ATLAS with a taste of Savoy

The third LHC data-taking period, called Run 3, will start in 2021. ATLAS detector is currently undergoing maintenance and improvement work, in particular to select even better the electrons and photons emitted in a wide variety of the processes studied at the LHC.

Up to now, the very fine-grained information produced by the ATLAS electromagnetic calorimeter was grouped in “trigger towers” to limit the number and hence cost of trigger channels. Advances in electronics and the use of optical fibres now allow the transmission of a much larger amount of information at a reasonable cost, and the “super-cells” to be used in Run 3 will increase the number of trigger channels ten-fold.

Since 2012, the ATLAS LAPP team has developed a part of the electronics responsible for managing this very high data volume of about 25Tb/s. These cards - called “LATOME” after famous savoyard cheese, tome des Bauges - calculate energy and time of the signals received in the “super-cells” and send this information to the trigger system to make the final decision. In 2019, 150 boards were produced and tested in the laboratory. They are currently being installed in the ATCA crates in the electronics room, 100 meters below the ground, next to the ATLAS detector.

LAPP also developed the IPCM card which allows to control the boards in the ATCA crate (including LATOMEs) and which are used by many ATLAS detector sub-systems.

The LATOME team posing with the last fully equipped ATCA blade which carries 4 LATOME cards in front of the ATCA crate test station used during the production. The LAPP group is also responsible for their installation at CERN and the associated software. From the left : Thibault Guillemin, Luka Selem, Nicolas Dumont Dayot, Nicolas Chevillot. Sébastien Cap, absent on this picture having left the LAPP at the end of 2019, was responsible for the design and production of the LATOME cards.

Fatih Bellachia, software engineer, works on ATLAS since 2003. He holds one of the IPMC control cards developed at LAPP.

The completion of this project is one more step in the laboratory long-term work on the ATLAS electromagnetic calorimeter. It will have an important impact on the physics studied at LAPP, including searches for new phenomena beyond Standard Model in the final states of two photons or two electrons ; precise studies of the Higgs boson decays, or the measurements of the diboson and dielectron production at the LHC.

Selection efficiency of electrons produced in Z Boson decays, as a function of their energy. Le blue curve expected for Run 3 is calculated with the same data rate as for Run 2 (black curve). Le red curve represents the efficiency if the LHC produces more collisions than expected and the rate per event must be divided by 2.

The development of the LATOME cards was also supported by University Savoie Mont-Blanc in the context of the Appel à Projets Recherche 2014-2017.

More information :

Contacts : Thibault Guillemin thibault.guillemin@lapp.in2p3.fr Tetiana Berger-Hrynova hrynova@lapp.in2p3.fr