# Overview

The Global Feature Extraction (gFEX) system is one part in a series of updates as part of the ATLAS Phase-I upgrade. At the start of Run 3, scheduled to begin in 2021, the L1Calo system's new elements depicted in this schematic, in addition to the gFEX, include: PPM Optical Plant, Hub, ROD, as well as two other Feature Extractors: the eFEX and jFEX. The gFEX module is a new technological addition that will allow for the use of full-scan algorithms and triggering of new features due to its ability to online scan the calorimeter using only one module. The TDAQ Phase-I Upgrade Technical Design Report, gFEX Technical Document, and gFEX Technical Specifications Document have more information. These manuals, and many other gFEX-related references, can be found in the 'Studies and Papers' tab.

This is the current production version 4b of the gFEX board. Click on the image to access a brief (public) overview of the development of the gFEX from a 2016 conference.

More specifically, the gFEX module is a Level 1 jet trigger system, running at 40MHz, which selects large-radius jets, typical of Lorentz-boosted objects, by means of wide-area jet algorithms refined by subjet information. The architecture of the gFEX permits event-by-event local pileup suppression for these jets using baseline subtraction techniques developed for offline analyses. The gFEX architecture is also suitable for other global event algorithms such as $$E_T^\mathrm{miss}$$ and centrality-related observables. The gFEX will substantially enhance the selectivity of the L1 trigger and increase sensitivity to key physics channels. The TDAQ level-1 gFEX upgrade proposal is available here. Click on the image to access approved public jet trigger plots for collision data that may be used for conferences and similar events.

The Phase-II upgrade is already scheduled for late 2023. This diagram gives an overview of the three major upgrade projects on the TDAQ system: the L0 trigger, DAQ, and EF systems. The gFEX module will be a part of the Phase-II level-0 trigger, which is itself an evolution of the Phase-I level-1 trigger. More information on the Phase-II upgrade can be found at the ATLAS Phase-II Letter of Intent (CERN-LHCC-2012-022. LHCC-I-023).