Expected Performance of the ATLAS Inner Detector

The ATLAS experiment at the CERN Large Hadron Collider (LHC) has started taking data last autumn with the inauguration of the LHC. Since then, the detector has been commissioned and calibrated in the ATLAS cavern. The ATLAS Inner Detector (ID) placed within a 2 T solenoid magnetic field, is a tracking system for charged particles based on three technologies: silicon pixels, silicon microstrips and straw drift tubes. The LHC physics discovery potential sets stringent requirements on the performance of the ID, specially in terms of pattern recognition, tracking, momentum and vertex resolution and low radiation length to minimize the material effects. After a brief description of the detector design, the expected performance for identifying and reconstructing single particles with transverse momentum pT > 0.5 GeV will be described as well as the detector’s vertexing and b-tagging capabilities. The effect of the detector material on the reconstruction of electrons and photon conversions will be presented. Finally, cosmic ray results that verify so far that the detector is ready to fulfill the expected performance specifications will be outlined

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements