The design and performance of the ATLAS Inner Detector trigger for Run 2 LHC Collisions at √s=13 TeV

The design and performance of the ATLAS Inner Detector trigger algorithms running online on the High Level Trigger processor farm with the LHC Run 2 data with collisions at both 50 ns and 25 ns are discussed. The HLT Inner Detector tracking algorithms are essential for the identification of nearly all physics signatures in the ATLAS trigger system. In order to deal with the expected higher rates for LHC Run 2, the Inner Detector trigger was redesigned during the 2013-15 long shutdown to satisfy the demands of the higher energy LHC operation. The detailed performance of the tracking algorithms with the Run 2 data taken in 2015 for the different trigger signatures in terms of both efficiency, and resolution is presented. The online processing times for running trigger tracking for the different trigger signatures are discussed in detail. Where appropriate, comparisons are made between the new strategies for Run 2, and the strategies adopted previously in Run 1. These comparisons demonstrate successful application and superior performance of the strategies adopted for Run 2.